milk meat hygiene

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PART II: MILK HYGIENE AND PUBLIC HEALTH 
Chapter 3 
INTRODUCTION 
K.G. Narayan, A.A. Sherikar, S.B. Majee 
 
Milk Hygiene is one of the components of Veterinary Public Health, i.e. Hygiene in relation 
to production of milk and milk products, is the area of concern primarily because a Veterinarian 
has a professional obligation to ensuring safety of the consumers, i.e. Public Health. The 
Veterinarian's activities start from the udder of a milch animal and extends to the consumer's table. 
Milk from an apparently healthy animal is pure, clean, safe, sound and wholesome. These 
properties define almost all desired characteristics of milk. Pure means unadulterated, clean, safe, 
sound and wholesome are the characteristics which are ensured by a Public Health Veterinarian 
who practices food, sanitation, safety, protection and preservation- all of which taken together 
comprise Food Hygiene. Food Hygiene has to be so adapted as to become a way of life. Its 
necessity has arisen because after the let down of pure milk, it becomes prone to contamination. 
Deliberately or inadvertently the natural purity and wholesomeness are altered and therefore 
deliberate, planned and appropriate interventions are required to ensure the protection and 
maintenance of the natural purity and wholesomeness. Knowledge gained in courses on Hygiene, 
Animal Products Technology and Microbiology form the base for this course. Practice of animal 
hygiene, particularly in milking parlour, will reduce microbial load, since milk and its products 
being nutritious foods, are also nutritious growth media for microbes. The presence of microbes 
in milk may cause spoilage and lead to much economic loss. Pathogenic microbes present in milk 
and its products may cause serious infections and intoxication among consumers. Public Health 
Veterinarian's primary responsibility therefore, lies in ensuring safety to consumers of milk and 
milk products. 
 
Milk. 
Milk may be defined as the wholesome, fresh, clear lacteal secretion obtained by the 
complete milking of one or more apparently healthy udders, excluding that obtained within 15 
days before or 5 days after calving or such periods as may be necessary to render the milk 
colostrom free, and containing the minimum prescribed percentage of milk fat and milk solids-
not-fat. 
 42 
Milk products. 
 Milk products are edible products, prepared necessarily from liquid milk or powdered 
milk, either by adding nuts, fruits, cereals etc., or prepared by changing the form of the milk itself 
without any addition before consumption. 
 
Pasteurization. 
 The term 'pasteurization', as applied to market milk refers to the process of heating milk 
to at least 63C (145F) for 30 minutes or 72C (161F) for 15 seconds in approved and properly 
operated equipment. After pasteurization, the milk is immediately cooled to 5C (41F) or below. 
Application of the knowledge of microbiological growth requirements will enable one to 
device measures to prevent growth of microbes acquired by milk, e.g. the application of low 
temperatures. Similarly, methods of preservation like pasteurization, sterilization and cooking 
applied to milk will take care of surviving microbes. In all these processes there still remains a 
chance of either inadequacy of treatment and/or contamination after treatment. The legal 
definitions of milk and milk products, processes of commercial production of cheese, yogurt, and 
certain delicacies can be found in Dairy India (1997). Practical tests are so devised that the quality 
of milk can be tested from the first stage of its production through collection, procurement and 
processing to the final finished product ready for consumption. Remember that milk is perishable 
and its life is short. The test results therefore will have to be made available in short time. The tests 
are clearly defined; e.g. milk that clots on boiling cannot be allowed for sterilization. Laboratory 
support is required in Quality Improvement Programme and Total Quality Management, which 
involves the evolving of Hazard Analysis and Critical Control Point (HACCP) approach from the 
farmer's milk to the various processing units of the dairy industry. Dairying is based on milch 
animals, viz. cows and buffaloes, the milk produced is the raw material of dairy industry (an 
industry is a group of productive or profit making enterprises). Cattle provide milk, manure, 
draught power and are also an asset used as collateral for loans. Cows and buffaloes subsist on 
agricultural residues and by-products to convert them to milk- a nutritious human food. However, 
seventy percent of milch animals are owned by 67% of land less, marginal and small farmers, yet 
they contribute 62% of total of 70.8 million metric tonnes of milk generated every year. The 
remaining 30% of milch animals are distributed among organized small and large dairies, but 
contribute only 38% of the total milk procurement. The dairy industry in India therefore rests 
 43 
largely on this cluster of 67% farmers unlike in European countries, Canada, Australia and USA 
where few large dairies contribute to the national bulk milk procurement. 
 
Dairy Industry in India. 
 Dairy Industry in independent India is almost synonymous with AMUL. The Kaira District 
Co-operative Milk Producing Union is known by the trade name AMUL (Anand Milk Union 
Limited). Sardar Vallabhbhai Patel founded it. The movement was against the exploitation of 
farmers by the middlemen/contractors. Shri Lal Bahadur Shastri, the then Prime Minister of India 
established the National Dairy Development Board (NDDB) to replicate the experiment made in 
Kaira district, called as "Anand pattern of dairy co-operatives" all over India. The NDDB through 
its "Operation Flood" programmes, was a grand success putting India on the global milk map. 
During 1995, the turnover of the Gujarat co-operative milk federation was Rs. 1400 million 
(equivalent to more than US $36 million). It was expected to be Rs. 1800 million (equivalent to 
more than US $47.5 million) during 1996. This placed the federation as the largest food industry 
and 23rd largest private firm in India (Kurien, June 13, 1996, RACS Conference, Chester, England). 
This federation enjoys 10% of Gulf Co-operation Council market share of ghee with annual sale 
of 400 tonnes. 
 
Structure of the Anand Pattern. 
 The basic unit of the Anand Pattern is the Village Milk Producers Co-operatives. All such 
village co-operatives are members of the District Co-operative Milk Producers Union. The district 
unions own cattle feed plants, facilities for production of semen and its distribution, routine 
emergency services, milk processing plants etc. The district unions in each state form a marketing 
federation, e.g. Gujarat Co-operative Milk Marketing Federation. All the state level federations 
combine together to constitute the National Co-operative Dairy Federation of India. At the center 
of this giant industry is the DAIRY FARMER. He employs professionals, owns and runs plants, 
operates chillers and processing plants. All that he has to do is to own one or two cows and become 
a member of the village dairy co-operative society. The dairy industry in India serves the interest 
of producers and consumers alike. The district unions have installed milk powder plants to 
conserve the surplus milk. Channeling all dairy commodity imports through the NDDB insulates 
the milk market. In industrialized nations there are heavy subsidies on dairy farming and the 
industry is fairly insulated from market variations. 
 44 
 
 
State Co-operative Milk National Co-operative Dairy 
Marketing Federation Ltd. → Federation of India 
   
 (For imports and exports) 
 NDDBDistrict Co-operative Milk 
Producers Union 
  
Primary Village Milk 
Producers Cooperative 
Societies 
  
Dairy Farmer 
 
 
Structure of a dairy co-operative "Anand Pattern" 
 
Size of Indian Dairy Industry. 
 There are about 57 million cows and 39 million buffaloes. About 70 million farmers are 
engaged in dairy activities. Indian Dairy Industry generates Rs. 58,000 crore annually and is 
expected to cross 88,000 crores in the 21st century. Milk production is growing at the rate of 4.51% 
and 60% livestock output is from the dairy sub-sector. 
There are 9.7 million farmers as members of 75,000 village dairy co-operative 
societies, each of which in turn are affiliated to the 22 state level federations marketing their 
products, competing among themselves and with private dairies. 
The figures of consumption of milk and milk products during 1995 (Table 1) speak 
of the volume and value of the products handled by the industry. 
 
 
Table 1: Consumption of milk and milk products (1995) and their values. 
 45 
Products Quantity (Tonnes) Value in Rs.(Crores)
Liquid milk 30,303,000 36,364
Butter (makkhan) 30,000 3,000
Ghee 906,000 9,060
Cream 17,000 85
Milk powder 2,23,000 1,338
Curd (dahi) 45,75,000 6,863
Butter milk/Seperated Milk 2,25,45,000 20,190
Khoa and condensed milk 9,00,000 6,863
Paneer, channa, cheese 2,10,000 1,050
Ice cream and Kulfi 50,000 600
Other milk equivalents 3,31,000 331
 
(Source: Indian Dairyman 49:46-47, 1997) 
 
Mechanization, automation, computerization have come up in a big way. Software has been 
developed and microprocessor based Integrated Milk Collection Systems are being installed in 110 
village co-operatives. PC-based online milk collection system takes care of all accounts, sales and 
purchases of the society apart from automating milk collection process, viz. Alpro Herd 
Management is an example, which keeps close watch on breeding, health, milk yield and related 
aspects. Alfa Laval Agri (India) Ltd., Karad (Maharashtra State) and Chitale Dairy Farm at Pune 
have sophisticated dairy facilities. 
 
Achievements. 
Advantages of Anand Pattern of Dairy Development. Grossly, the total milk production by the 
end of 1999 is estimated to be 76 million tonnes, however the per capita availability of milk is 
220g per day per individual, as against the ideal 400g-500g per day (Food Outlook FAO-1997). 
The actual milk consumed varies greatly; in the eastern region it is as low as 20g whereas in the 
western and northern regions it is 400g. Thus, about Rs. 50,000 crores (US $125 billion) flows 
back into rural economy each year to directly benefit the farmers. The country's imports of milk 
and milk products have virtually been reduced to nil. We have now started exporting milk products 
like butter, cheese, pedhas, rasogollas etc. to the Middle East and other countries. The dairy 
technology is being exported; e.g. Sri Lanka has gone in collaboration with NDDB to set up Kiriye 
Milk Industries. Khazagastan, formerly a part of the Soviet Republic had a dairy set up by the 
Dairy Board of India. Thailand, Vietnam, Iran and Pakistan have also entered into several 
collaborative programmes. 
 46 
 
Export Quality and its Control. 
 Dairy product export although had risen during 1994-'95, it has shown a decline during 
1998-'99. The main reason is the "quality" which has been questioned by the European Union 
Countries. According to World Trade Organization (WTO) and the Office of the International 
Epizootic (OIE) France, subsidies have to be removed, else the Indian dairy is likely to capture the 
markets in South Eastern, Eastern, Pacific and other countries in the region. To achieve 
international market credibility, emphasis on Good Manufacturing Practices (GMP) and Quality 
Assurance Programmes (QAP) have to be initiated by establishing the Indian standards, which are 
outdated, and for indigenous products, non-existent. 
The International Organization for Standardization (ISO) in 1987 published a series 
of standards on Quality Systems, popularly known as ISO 9000 family of standards. Some of these 
standards were revised in 1994 to make them more clear and understandable. The Bureau of Indian 
Standards (BIS) adopted the ISO-9000 as IS-14000 Series Standards. The BIS has now issued the 
equivalent Indian Standards as IS-9000 Series. The "Milk Fed" dairy, Punjab has been accredited 
with ISO-9002 and the BIS is accredited with the RVA i.e. Raad Voor Accreditive, Netherlands 
for certification of Quality Systems as per the internationally accepted criteria in India. The EC 
countries increasingly use ISO-9002 as precondition for export to those countries, since these 
provide standardized format for monitoring in-house QAP and Quality Control (QC). 
 
Review Questions. 
1. State in brief the model milk production system in India. Compare it with the system abroad. 
2. To which countries does India export its milk products? What are the difficulties faced by 
Indian exporters? 
3. What accreditation do the EU countries require? Why? 
 
Further reading. 
Prevention of Food Adulteration (PFA) Rules 1995 (up to Aug '95) in Dairy India Vth edition 
1997, 458-446, New Delhi. 
Chawla N K and Kumar R. 1997. International Food Laws and Their Implications for the 
Indian Dairy Industry. Indian Dairyman, 49: 107-114. 
Sood V. 1997. "ISO-9000 Certification" in Dairy India, Vth edition, 
 47 
 343-346; New Delhi. 
Operation Flood- A Reality. Indian Dairy Corporation Report, Baroda, Gujarat. 
 
 
 48 
Chapter 4 
MICROBIOLOGY OF MILK AND MILK PRODUCTS 
 Abhaya A. Sherikar and Sharmila B. Majee 
 
 Milk from an apparently healthy animal is relatively free of pathogenic bacteria. It, 
however, gets contaminated when comes in contact with the external environment. Lack of 
hygiene, unsatisfactory chilling facilities at district level, milk collection centres, improper post 
production storage and improper handling of milk and milk products lead to a serious deterioration 
in the microbiological quality of milk especially in developing countries like India. Thus it is only 
natural that a shadow of doubt is sometimes cast on the products produced by the unorganized 
sector. This is further accentuated by the fact that the use of low quality raw milk and recyling of 
unsold milk products lead to added microbial contamination. 
 Microbiological evaluation focuses on the hygienic quality of food as well as the sanitary 
conditions existing at the place of its manufacture and storage. It aims to determine the 
correlations between these two indelible factors. The primary purpose of microbiological 
surveillance of raw milk and finished milk products is to identify the threats to their safety and 
suggest what needs to be done to protect the health of consumers. Due to a lack of awareness, the 
consumers are not cognizant of the need for proper safety measures during production and sale of 
these products as their major consideration remains to be the sensory impact and price of the 
products. All these factors combined, relegate the safety and quality of milk and dairy products to 
an insignificant position. The quality evaluation/ standards for milk and milk products in India 
remain confined mainly to the determination of its chemical adulterants. The importance of 
microbiological (bacteriological) grading of milk has not yet been fully realised in spite of the fact 
that milk and its products are an excellent for the growth of pathogenic microorganisms and 
elaboration of their toxins. 
 Therefore, it is important to know the channels through which microorganisms gain access 
to milk and milk products during collection, processing and distribution and the possible methods 
of their control. The groups of microorganisms involved in these processes are noted in the 
appendix no. 1.49 
Sources of Contamination. 
I Raw milk. Routes of contamination of raw milk and the preventive measures to be adopted are 
as follows : 
1. Practice at organised and unorganised dairies. The following factors contribute to the 
microbial load of milk : 
a) Interior of the udder: Milk from an apparently healthy cow contains microorganisms which are 
generally acquired from the walls of the ducts along the teat canal, including those which normally 
exist in the udder. Some microbes may be introduced in the milk through the teat during treatment 
with contaminated intramammary preparations or from the environment of the animal. They are 
subsequently washed out in the first few streams of milk withdrawn from the udder. The microbial 
load in freshly drawn milk varies with individual animals. The cleanliness of quarters and the 
health of dairy animals contribute significantly in this regard. Usually the bacterial count of milk 
varies between 500 and 1000/ml. Deviations may, however, be noticed in case of some milk 
supplies. The elimination of disease producing bacteria in milk, e.g., Mycobacterium tuberculosis, 
Brucella sp.and Streptococcus pyogenes, pose a major public health hazard. Therefore, milk 
intended for human consumption should be obtained only from healthy animals tested regularly 
for tuberculosis and brucellosis, and all diseased animals should be removed from the herd. Cows 
should be stabled in clean stalls and pastured in drier areas, free of swamps and stagnant water / 
wash water that contaminate ( mainly with coliforms) the teat canals of the udder and later are 
discharged in the milk. A few streams of milk should therefore, always discarded before collection 
of milk. 
 
b) Environmental. The extent of the contamination of the flanks, tail and udder varies depending 
on the condition of the cow-shed. The microorganisms found in soil, animal discharges, straw, 
dust etc. accumulated on the surface of body get dislodged during the milking process and enter 
the pail contributing a load of 10,000 bacteria or more per ml. of milk. The presence of pathogens 
such as coliforms (fecal coliforms) cause what is known as summer complaint or infantile 
diarrhoea due to consumption of infected milk. Coliforms usually originate from dung of the cow 
and may be present in large numbers when hygienic conditions in the dairy are poor, and 
temperatures are high enough to encourage their multiplication. 
 Use of hygienic methods in the cow-sheds helps in maintaining clean stalls. Wiping of 
flanks and udder with a clean damp cloth just before milking and employing a small mouthed 
 50 
container for collection of milk or properly sterilised milking machine can also help in the control 
of contamination. 
 
c) Milker or Handler. Milkers and handlers suffering from disease, conditions such as typhoid 
fever, diphtheria, scarlet fever, septic sore throat and coughs and colds contribute to the 
transmission of these diseases to susceptible individuals by contaminating milk or milk products. 
Some of the most serious epidemics have their origin in infection from a diseased individual or 
“carrier” who has handled milk or utensils at one time or the other. The carriers, therefore, should 
not be allowed to handle milk or milk products. 
 
d)Utensils. Utensils are the most prolific source of microorganisms. A milk can or bucket 
improperly washed, inadequately sanitised or dried or a dirty milking machine are a fertile source 
of milk contamination. Apart from these, disease causing bacteria such as those of typhoid fever, 
may find their way into milk from utensils washed with contaminated water. 
 Contamination can be prevented by thorough cleansing, followed by sterilisation of 
utensils. After washing, buckets and milk cans should be rapidly dried and kept in a dry place. 
At the farm level, there is an utmost need of constant attention to details of hygiene and sanitation. 
Since man is a direct / indirect source of contamination, he should exercise every hygienic 
precaution to ensure safety of milk and milk products. 
 
e) Wholesaler, retailer and the vendor. The main sources of contamination of milk obtained from 
these three outlets are the milk cans and buckets used for transport of milk as well as the dippers 
used to draw milk from the cans. Some of the wholesalers or retailers also keep bulk containers to 
store larger quantities of milk. These containers if not cleaned well, are potential sources of 
pathogens that gain entry through contaminated water supplies, carrier individuals handling the 
milk and fecal contamination. Improper washing and cleansing of the cans / containers can cause 
a build up of milk residues that facilitate the growth of micro-organims like Staphylococcus 
aureus, Bacillus cereus and fungi. These organisms may get released into milk during refilling of 
the can. Spoilage organisms such as Bacillus sp. as well as yeast and molds, thrive in milk 
adulterated with contaminated water. 
 The best preventive step would be to improve the standard of personal hygiene of the staff 
and cleansing the containers with hot water and caustic soda / bleaching powder (2%) immediately 
 51 
after emptying their contents and allowing them to dry before refilling. The dipper should also be 
washed and sterilised in a similar manner. 
f) Storage of raw milk in chilling tanks at milk processing units and bulk containers. Milk brought 
to the cities by tankers is first emptied into chilling plants (bulk containers) at the milk processing 
units where the temperature of milk is maintained between 0° - 4°C before pasteurisation. 
Contamination with S.aureus, yeasts and coliforms at this point occurs mainly through improperly 
cleaned or sanitised milking equipment where moist milky residues allow rapid multiplication of 
the organisms. Secondly, the water used for washing the bulk tanks may be nonpotable having 
high coliform counts. Mastitic streptococci are derived only from mastitis milk mixed with other 
milk at the farm level and primary milk collection centres. Mold contamination occurs mainly 
through aerosols under humid conditions within improperly cleaned and disinfected plants. Both 
yeasts and molds reduce the keeping quality by increasing the acidity in milk and developing off 
flavours. Organisms causing enteric fever and dysentry like Shigella sp. are also contracted 
through bad hygiene. 
 Control measures include immediate washing of bulk containers / tanks with hot water, 
caustic soda / bleaching powder after emptying milk, to remove milk debris and sterilising them 
wih the help of hot steam jets, which also kills the adherent bacteria and yeasts. Proper cleaning 
of plant premises with hypochlorite also reduces the load of bacteria and molds in the atmosphere 
of the processing plant. 
 
g) Transport of raw milk by rail / road tankers. Improper maintenance of milk tankers adds to 
the microbiological contamination in milk and, therefore, the longer the time the milk remains in 
the tankers, higher will be the load of bacterial and fungal agents. The problems of transportation 
of milk in India are many since the ecological and the local climatic conditions tend to vary from 
regionto region. During monsoon , for example, one has to cope not only with rain and floods but 
also with the dislocated rail and road transport. The bacterial counts and species differ with 
seasons. Pathogenic bacteria, yeasts and mold multiply rapidly in summer as compared to winter 
or monsoon seasons. One of the sources of contamination in tankers is the accumulation of (milk) 
solid residues inside the gauges, taps, pipes etc. which act as a focus for microbial growth 
and which contaminate milk during transport. Some of the psychrotrophs such as Pseudomonas 
sp.produce extracellular enzymes which produceoff flavours. The organisms are heat resistant and 
survive even after pasteurisation of milk resulting in loss of flavour, texture and stability of milk. 
Spore formers are found to be least in number during the monsoon season due to availability of 
 52 
fresh green fodder, ample water and a relatively dust free environment. Presence of pathogens, eg., 
S.aureus, enterotoxigenic E.coli, B.cereus etc. that originate mainly from the handlers at the 
source of milking, remain in milk, producing heat stable toxins which are harmful to the consumers 
and which are not readily destroyed by heating during pasteurisation. Hence, an overall absence 
or very low level of pathogens is requires to be ensured especially in tanker milk to be pasteurised. 
The load of organisms can be lowered by taking adequate hygienic precautions at the farm as 
well as by regular cleansing and proper maintenance of tankers used for the transport of milk. 
 
II. Psteurised milk. 
 1. Production of Pasteurised milk. Presence of thermoduric (surviving but not growing at 
pasteurisation temperature) and thermophilic (growing at and above pasteurising temperature) 
bacteria in milk indicates unhygienic conditions at the farm. The conditions are generally 
associated with careless handling of milk and use of unclean utensils and equipment. Thermoduric 
bacteria, include spore formers like Bacillus sp., and (largely) non-spore forming, heat resistant 
microorganisms e.g., micrococci, microbacterium and streptococcus sp. growing on the surfaces 
of improperly washed / sanitised utensils, preheating equipment in the processing plants and the 
pasteurising equipment. Control of thermoduric species is an operational problem involving both 
dairy farms and milk plants. Thermophilic species are spore forming, heat loving microorganisms 
(growing best at 55°C), eg., Bacillus sp. and Lactobacillus thermophilus and their presence in milk 
in large numbers indicates unduly long exposure to pasteurisation temperature and in some 
instances to other insanitary practices such as : (1) repasteurisation of milk, prolonged holding of 
milk or cream in vats and stagnant milk in blind ends of piping at pasteurisation temperatures, 
(2) continuous use of preheaters, long flow holders or vats for more than 2 hours without 
periodically flushing out equipment with hot water, (3) passage of hot milk through filter cloths 
for more than 2 hours without replacing cloth, (4) residual foam on milk which remains in vats 
when emptied at the end of each 30 min. holding period and, (5) growth of thermophiles in milk 
residues on surfaces of pasteurising equipment. 
 Contamination of pasteurised milk with psychrophilic bacteria, e.g., Pseudomonas sp. and 
Achromobacter sp. may occur due to polluted water supplies that are used for rinsing equipment, 
accumulated residues and poorly sanitised equipment and containers. Better sanitation of 
equipment and a reduction of storage period between pasteurisation and consumption are as 
essential for controlling milk contamination. 
 
 53 
2. Cooling. The pasteurisation or sterilisation is immediately followed by cooling of the heated 
product wherein cold raw milk is used to cool the outgoing hot milk. Contamination of milk can 
occur at this stage if care is not taken to use leak proof equipment, maintain the heated milk at a 
higher pressure than the coolant, maintain gaskets and seals hygienically and keep appropriate 
pressure on the processes in the plate heat exchangers. The temperature should be about 10° C or 
less to retard the growth of surviving or contaminating microorganisms, besides taking care of the 
subsequent warm up of the product during packaging. 
 
3. Packaging. The aspects of packaging important from the microbiological point of view are: 
a) Equipments. Filling equipment are complex and need to be dismantled for thorough cleaning 
and sanitising in order to check contamination of the finished product. The measuring devices, 
valves, etc., require proper cleaning between runs. Another potent source of contamination is the 
condensate getting into the container during packing. This can be prevented by providing efficient 
drip reflectors in the equipment. 
 
b) Packaging materials. Glass has now been replaced by paper and plastic containers. The glass 
containers, though sterile when manufactured, get contaminated due to faulty storage practices and 
by repeated use. Disposable paper and plastic containers should be of a good initial microbiological 
quality, as they are liable to get contaminated on storage. 
 Sealing equipment being complex, may present serious microbiological problems. 
Therefore, they should be of proper design, and should always be cleaned and sanitised before 
use. Proper handling of the packaged product is essential to avoid breaks in the package or closure, 
as it may allow entry of microorganisms and increase the chances of product spoilage especially 
during long storage. The chances of contamination are further increased in presence of moist 
surfaces. Use of aseptic packaging such as tetrapacks, tetrabrick, zupack and self pack involves 
the treatment with hydrogen peroxide. The risks of contamination are connected with sterilisation 
of packaging material, especially when rolls of paper are changed. Faulty sealing of packs, along 
with sources like worn out gaskets, condensates at filling pipes etc. may add to the contamination. 
During marketing and distribution of packed milk, the microbial load in milk is likely to increase 
if refrigeration conditions are not satisfactory especially during transportation, and at wholesale 
centres, retail shops and in the household. Once the temperature of milk rises above refrigeration, 
the microbial counts tend to increase. 
 
 54 
III Ultra high temperature (UHT) treated milk. Ultra high temperature treated milk is 
generally sterile. The presence of thermoduric organisms, i.e., heat resistant spoilage organisms is 
rare, whereas the only organisms to survive temperatures of 135-150oC are spores of thermophilic 
bacilli, e.g., those of Bacillus stearothermophilus and sometimes mesophiic bacilli and clostridia. 
Due to UHT processing, aseptic packaging and improved control on post-pasteurisation 
contamination, the psychrotrophs such as certain species of Bacillus and clostridia are emerging 
as the major spoilage organisms in UHT milk. The spoilage of UHT milk is mainly due to faults 
in filling and scanning of packs during packaging, e.g., Pseudomonas sp., micrococci, coryneform 
bacteria, enterococci, Bacillus, yeasts etc. which may modify the milk such as coagulation / 
floculation or by production of off flauours. In UHT milk, such problems generally do not arise 
since milk becomes sterile and has long keeping quality. However, proper storage is required to 
avail higher shelf life. 
 
IV. Milk products. 
1. Cream. Cream is used for manufacture of milk products like butter, ghee, ice-cream and various 
desserts. The following factors can affect the microbiological quality of cream 
a) Quality of raw milk. The microbiological quality of raw milk used for separation of cream has 
a direct bearing on the quality of cream obtained. Poor quality raw milk with high spore and 
thermoduric counts results in poor keeping quality of cream since these organisms can survive 
heat treatment. Control measures include hygienic milk production at the farm level. The milk 
should not be stored for long periods or at high temperatures. Psychrophilic and psychrotrophic 
counts may increase if the milk is held at lower temperatures for long periods. As cited elsewhere 
the enzymes of the organisms are heat stable and produce proteolytic and lipolytic spoilage of 
cream. Therefore, the temperature of storage of milk should invariably be 4°C. 
b) Separation process. Cream separated onthe farm has poorer hygienic and microbiological 
quality than that separated in dairies, since dirty separators in the farms tend to add contaminants 
to the cream. After every run, the milk constituents in the bowl and between the discs must be 
carefully removed. Otherwise, the micro-organisms may proliferate and contaminate subsequent 
batches of cream. 
 Brushing, draining and sanitising of separator parts is advisable. Conventional separators 
are used at 35°C - 45°C, whereas in case of modern ones, a lower temparature of 25-30°C is 
maintained. During the separation process bacterial cells, spores, dirt etc., are removed by high 
 55 
speed centrifugal methods which also helps reduces spore count since aerobic sporeformers tend 
to form chains and are removed as slime from milk. 
 
c) Holding of cream before processing. Cream held at 18°C carries high counts of thermodurics. 
When held at 5°C cream harbours more of psychrotrophs. Prolonged holding of cream should, 
therefore, be avoided at farm level because under farm conditions microbes multiply faster due to 
availability of favourable conditions. Cooling of cream after separation should be rapid. Warm 
cream should not be mixed with previously cooled cream because it can raise the temperature of 
the entire lot of cream leading to growth of microorganisms. Processing of cream involves the 
following steps :i) Standardization. Separation of cream carried out at 40°C is unsafe. It is a 
congenial temperature for microbial growth. Hence, contaminated skim milk would ‘seed’ the 
cream with microbes. As a control measure, the standardised cream should always be heat treated, 
cooled and packed immediately. 
ii) Homogenisation. During homogenisation, both the milk and cream may get contaminated 
(during the holding process) as the bacterial clumps disperse in the cream. Lipolytic changes 
occur in the cream by the action of the bacterial lipases leading to rancidity. These problems can 
be controlled by homogenising the cream at the penultimate stage of heat treatment. 
iii) Heat treatment (pasteurisation / sterilisation). Higher heat treatment applied to cream may 
have an adverse effect on its keeping quality due to an increase in the germination rate of surviving 
spores, (especially after a relatively drastic exposure). The friction process has been successfully 
applied to creams with 12 - 33% fat content without any losses in the quality of the cream. iv) 
Freezing. It enhances the keeping quality of cream by checking the growth of microbes and retains 
the original nutritive value of the product, unlike heating. However, freezing does not reduce the 
microbial load appreciably, although there is some reduction in microbial count due to mechanical 
injury to the cells caused by the formulation of ice-crystals. v) Holding of cream after processing. 
Storage of processed cream prior to packaging should be avoided in order to reduce the microbial 
proliferation (especially the increase in psychrotrophs when stored at 5°C). 
 
d) Packaging/Canning. The packaging materials are manufactured in almost a sterile form. 
However, any lapse in their hygienic storage and use during (aseptic) packaging and sealing could 
result in the entry of microbes to milk products at this stage. Unhygienic surroundings like 
presence of vegetation, decomposing materials and drains may contaminate the atmosphere with 
bacteria, yeasts and molds which might enter the product during filling. Therefore, the process of 
 56 
filling the cans may provide opportunities for the contamination of milk products. To prevent this 
the most common method is to give a UHT treatment (140°C for 2 seconds) before canning the 
cream to kill spores and a milder heat treatment to the cans after filling to destroy the 
contaminants. 
 
e) Storage and distribution. Cream can be stored and handled for variable lengths of time, 
preferably at or below 5°C. It should be distributed within 3 hours of its removal from cold storage. 
Since these conditions cannot be fulfilled by small vendors, the bacteria are liable to proliferate, 
forming bacterial clumps and rancidity, and other defects caused by microbial metabolites. 
 In order to control microbial growth during storage and distribution the following measures 
can be adopted : i) maintenance of milk and cream at 5°C during different stages of storage, ii) a 
prompt distribution to check spoilage problems, iii) proper aseptic packaging without leakage and 
iv) utilisation of good quality raw cream, which may help to avoid microbial defects in sterilised 
and UHT treated creams. 
 
2. Butter. Microorganisms present in butter may be derived from a variety of sources. 
a. Raw material (milk / cream). Butter made from cream collected daily is superior to cream 
collected on alternate days or from bulk tank milk. The thermoduric lipase secreted by 
psychrotrophic bacteria in bulk milk results in the production of high free fatty acid content and 
thereby affects the composition of cream and butter produced from it. Cream produced in this 
manner exhibits slow acid development during ripening due to adverse effects of liberated free 
fatty acids. Cream is generally separated in the factory itself from the milk received from different 
sources. If the milk contains a heavy microbial load, so would the cream. Sweet cream has a 
lower microbial load as compared to sour cream. Sometimes, the cream is accumulated before 
churning into butter. During this process, microbial growth may occur. If pasteurisation is carried 
out before churning, subsequent microbial contamination may take place from sources like 
equipment, wash water, air and packaging material. However, if the original microbial load in 
cream is high, bacteria may survive even in the pasteurised cream. Control measures include, 
hygienic production of milk and cream, proper quality control of cream before butter making and 
avoiding storage of cream at high temperature. 
b) Equipment. Among equipment, butter churn is the most important source of contamination with 
psychrotrophs, yeasts (Candida and Torula sp.) , and molds (Geotrichum sp.). Wooden churns 
with irregular surfaces are the most common sources making the removal of solid particles and 
 57 
sanitising difficult. Molds penetrate deep into the cracks and crevices of wood and serve as a 
continuous source of contamination. Therefore, metal drums are preferable (from the sanitary point 
of view).Components of the pasteuriser including pipelines, pumps, valves and coolers may also 
serve as additional sources of contamination. 
c) Water supplies. During butter manufacture, water is used for various purposes, i.e. flushing 
residual cream from holding vats into churns (for dilution of cream), wet salting and/or for 
adjusting the moisture content of butter. It is also used as breakwater and chilled wash water, and 
for washing butter granules during the continuous butter making process. Non-potable water, 
containing psychrotrophic bacteria ( proteolytic and lipolytic) are known to cause butter spoilage 
e.g., Achromobacter putrescens causes putrid butter and Pseudomonas sp. gain access into butter 
if well water is used for washing purpose. Psychrotrophic bacteria grow in chilled water in dairy 
tanks particularly when water contains organic matter and has not been effectively chlorinated. 
Coliforms and some heat resistant clostridia and bacilli have been found to occur in natural water. 
 One of the most effective control measures is the chlorination of water supply by adding 
required concentration of chlorine. In routine practice,1-5 mg/lit residual chlorine is found to be 
effective in ensuring good quality butter. 
d) Air. All dairy factories do not have a separate packing room and do not maintain high standards 
of hygiene in butter packing and printing rooms.Thus butter often gets exposed to air for long 
periods prior to or during packing and gets contaminated predominantly with bacteria followed 
by yeasts and molds. Psychrotophs and mold spores remain suspended in the air and stick to walls 
and wooden structures in the packing room. Movement of workers, ventilation fans, drains and 
dust from surrounding areas also contribute to the microbial load of butter. Control measures 
include cleaning of surfaces with hypochlorite based detergents and fumigation of rooms. 
e) Personnel. The persons involved in manufacture and handling of butter may themselves 
introduce microorganisms into butter through contaminated hands, clothing, mouth and nasal 
discharges, sneezing particularly at the packaging stage. Therefore, persons, suffering from 
respiratory diseases should not be allowed to handle butter. The personnel dealing with butter 
should wear gloves and masks and wash them in chlorine solution after use to prevent 
contamination. 
 
f) Butter colour. Annetto, the colour used for incorporation into butter is practically devoid of 
microorganisms. However, if it is kept in open containers or mixed with water in unclean 
containers, the butter is likely to be contaminated. 
 58 
 
g) Packing materials. Normally parchment paper is used for packing butter. However, sometimes 
this paper may get contaminated especially with molds during transporatation or storage. Use of 
dry parchment and/or treatment with hot brine or antifungal chemicals like sorbic acid / potassium 
sorbate, propionic acid /calcium or sodium propionate or benzoic acid/ sodium benzoate may 
reduce mold contamination. A combined treatment of hot brine and sorbic acid (0.5%) for 24 
hours is recommended. Nowadays aluminium foil and other laminates are becoming increasingly 
popular for butter packaging in different countries due to their attractive appearance and protection 
against chemical deterioration of butter. For bulk packing of butter, the containers are lined with 
parchment paper. Use of polythene films is widely practised in different countries due to several 
advantages including less contamination. 
 
3. Cheese. Cheese can get contaminated with microbes at the following stages: 
a) During manufacture. Lactic acid fermentation occurs when cheese is being drained. If the lactics 
are ineffective and/or contamination with other microbes is unduly heavy, abnormal changes in 
cheese may take place. In the cheese made from microbiologically poor quality raw milk, gas 
producing organisms produce off flavours as well as gas holes. Lactose fermenting yeasts and 
Bacillus sp., cause gassiness and other defects during ripening. Species of clostridia cause off 
flavours in either raw milk or pasteurised milk cheese, if the lactic starter bacteria are not 
functioning properly. These bacteria when present, competitively inhibit starter organisms with 
results that do not become evident till the curing process, where body and flavour of cheese are 
affected, eg. acid proteolytic bacteria produce a bitter flavour or Leuconostoc sp. may cause holes 
or openess in cheddar cheese from pasteurised milk. Cottage cheese is especially subject to 
spoilage during storage. If the starter bacteria produce insufficient acid, cream is added or curd is 
not formed, which results in growth of undesirable organisms eg. Pseudomonas sp. or Alkaligenes 
sp., which cause proteolysis, gas sliminess, off flavours etc. rendering the cheese gelatinous or 
slimy. 
 Control measures include use of hygienically produced raw milk which, after 
pasteurisation, could be rendered sterile for cheese processing. Regular examination of starter 
cultures to weed out the contaminating bacteria, yeasts and molds is essential. 
 
b) During ripening. Cheese normally undergoes physical and chemical changes resulting from the 
action of enzymes released by the autolysed bacteria that propagate in it during manufacture. The 
 59 
spoilage also occurs on account of the action of the microorganisms that grow during the ripening 
period. Growth of undesirable organisms results in the alterations of texture, body, general 
appearance and flavour of cheese. Cheese may also be subjected to late gas formationcaused by 
lactate fermenting clostridial sp. and also by the bacilli, propionic bacteria or heterofermentative 
lactics. Gas holes or eyes are desirable in swiss and related cheeses but not in other varieties of 
cheese. Cracking or splitting of swiss cheese by gas or production of too many misshapen eyes 
may be accompanied by production of undesirable flavours eg. butyric acid from anaerobes. 
Bitterness may be caused by lactic streptococci, coliforms and micrococci. Yeasts impart to it a 
sweet fruity flavour. Putrefaction can occur locally or generally in cheese when acidity produced 
by the lactics is insufficient or acid has been destroyed by a lactose fermenter. eg. Clostridium sp. 
Discolourations of ripening cheese may result from action of microbes or compounds produced 
during cheese making, the added colouring material such as annatto (used in cheddar cheese) or 
simply by action on the pigments of various bacteria. Sulfhydryl groups formed by bacterial action 
give a pink to muddy appearance to annatto. Reddish brown to grayish brown colours sometimes 
result from oxidation of tyrosine by bacteria growing in soft cheeses. Rusty spots of cheddar and 
similar cheese are caused by lactobacillus sp., while yellow, pink or brown spots in swiss cheese 
are due to Propionibacterium sp. 
 Control measures for preventing undesirable changes in cheese during ripening include 
lowering the moisture content of cheese, increasing salt content, reducing its lactose content with 
the help of starter bacteria, proper packaging and coating of cheese with paraffin -wax, and regular 
cleaning and sanitising of ripening rooms to prevent contamination of cheese with yeasts and 
molds. 
 
c) Finished product. The perishability of cured cheeses increases with their moisture content. 
Therefore, soft cheeses like Limburger and Bire are most perishable and hard cheeses like cheddar 
and swiss most stable. Molds are mainly responsible for damaging cheese by growing in the cracks 
and holes in the cheese. Even cheeses which are partly dependant on molds for ripening are 
damaged by other pathogenic molds. Most natural cheeses have rinds that protect the anaerobic 
interior but are not dry enough to prevent mold growth. The acidity of the cheese is not a deterrent 
to growth and storage temperature is not too low for growth of molds. 
 Control measures include, proper ripening and curing of cheese with a low moisture 
content and storage of cheese at lower temperatures. 
 
 60 
4. Yoghurt. In view of the high acidity and product of the 2 starter cultures, yoghurt can be 
considered a hygienically safe product. Salmonellae, coliforms and spoilage organisms are unable 
to survive in natural yoghurt. Yeasts and molds are mainly responsible for the deterioration of 
yoghurt quality as these organisms are not affected by low pH. Fruits used in some stirred 
yoghurts can be a potent source of contaminantion of surfaces, eg., lactose fermenting 
Kluyveromyces sp. Molds do not pose a serious problem. Molds growing at the interface are 
dislodged during agitation and thereby suppressed. The activity of starter cultures used for 
manufacture of yoghurt needs to be critically monitored periodically to get a product of uniform 
quality. 
 
5. Fermented milk. Various lands of fermented milk are used : 
 a) Low acid type. 
i) Cultured butter milk. The most common defect is poor stability which results in whey 
separation. This can be prevented by addition of gelatin or fat to milk, or 10% milk culture of 
Lactobacillus bulgaricus. Too little acid production may be due to inactive starteror inhibitory 
substances such as bacteriophages in the milk. Therefore, the use of phage insensitive strains is 
advocated. 
 
ii) Cultured sour cream. Since it is an extremely viscous product, agitation of ripened cream 
should be kept to a minimum. In order to increase viscocity, cooling and ageing at 5°C for several 
hours is 
practised. Microbiological quality is similar to cultured butter milk. 
 
b) Acid-alcohol type. 
i) Kefir. Kefir is an acidic, mildly alcoholic and a distinctly effervescent product which is 
manufactured from the milk of goat, sheep and cow by fermentation. Traditional kefir contains 
70% of lactobacilli, 20% of streptococci and 5% of yeasts. Micrococci, spore forming bacilli and 
coliforms may be present as contaminants. The advantages of fermentation are acidification of 
milk which increases its storage ability and prevention of putrefaction, and growth of food spoilage 
organisms. 
 
ii) Kumiss. It is an effervescent, acidic, alcoholic and fermented milky white greyish liquid which 
is prepared primarily from mare’s milk. Organisms responsible for fermentation of this product 
 61 
are similar to kefir. Lactic streptococci, coliforms and sporebearing bacilli may contaminate the 
starter cultures. 
 
c) High Acid type. 
i) Bulgarian sour milk. The product is similar to yoghurt and Bulgarian butter milk is similar to 
cultured butter milk. In Bulgarian butter milk, high incubation temperature may lead to defects 
caused by growth of contaminating bacteria escaping heat treatment. 
d) Medium acid type. 
Acidophilus milk. Lactobacillus acidophilus, which is used as a starter in the preparation of 
acidophilus milk, is unable to multiply rapidly in milk. It is easily overgrown by contaminating 
organisms. Thus it loses its viability in the product, hampering proper establishment of the 
organism in the gastrointestinal tract for therapeutic purposes. Contamination can be avoided by 
strictly following the sterilisation protocol for milk and standardized bacteriological procedures 
while transferring the culture. Acidity, should not exceed 0.6 - 0.7% and a storage temperature 
should always be maintained between (5°C - 20°C). Other fermented milk products include leben, 
taette, skyr and lactic beverages like drinking yoghurt, acidophilus drink and alcoholic milk 
beverages. The whey based beverages are rivella and acido-whey. 
 In case of fermented milk products, faults occur mainly due to incorrect fermentation, 
gelling and treatment, and recontamination of the products during handling. The following 
precautions need to be taken to provide high quality, nutritionally, wholesome and safe fermented 
milks. i) Fermentation process with controlled temperature and time. ii) Gel breaking / stirring 
under constant conditions. iii) Aseptic filling. iv) Hygienic packaging and storage. 
 
6. Indigenous fermented/ coagulated milk products. 
a) Dahi and dahi based products. 
i) Dahi. Dahi forms the base for chakka, shrikhand and shrikhandwadi. It also helps in the 
preparation of lassi, butter and ghee (which can also be prepared from cream). Therefore, the 
microbiological quality of dahi tends to influence the quality of related products. Milk of good 
quality (pasteurised) should be used for preparation of dahi. Most halwais and vendors use raw 
milk with high microbial load which increases on subsequent unhygienic handling. This causes a 
reduction in the quality of dahi. Utensils used in the preparation of dahi when inadequately washed 
between two settings of dahi are responsible for the high total count. Unclean fridge handles and 
tables contribute significantly to the load of aerobic sporeformers, S. aureus, faecal steptococci 
 62 
and coliforms. Floors and other sites in the plant are a potent source of yeast and molds, aerobic 
spore formers and spoilage organisms on account of the use of dirty cloth to wipe the surfaces by 
handlers who are not fully aware of the good sanitary practices. 
 Adoption of good hygienic practices along with the use of good grade milk can reduce the 
level of contamination. 
 
ii) Chakka, shrikhand and shrikhandwadi. Products (chakka) which are directly derived from 
dahi are found to add to the contamination because of poor handling of dahi by handlers, and use 
of unclean muslin cloth for draining dahi. The microbial load so generated is transferred to 
shrikhand during its preparation (from chakka). Sugar added to shrikhand may also contribute to 
the microbial load along with shrikhand mixes which may get contaminated on mixing and 
handling in dirty utensils. On organised dairy farms, contamination with spoilage organisms occurs 
mainly at the point where chakka is mixed with sugar and shrikhand mixes in large containers that 
contain sticky residues. A thorough cleaning and sanitising of containers between batches can 
alleviate the problem. At the filling tanks, the nozzles and valves may carry accumulated residues 
of these products, thereby contaminating the product with toxigenic bacteria. Serial contamination 
may occur in improperly packed shrikhand. Contamination through lids and packing containers 
can also not be ruled out, especially where mechanical (man made) packing is carried out. Hence, 
gloves and masks should always be worn by the workers to reduce the level of microbes in the 
finished products. Since shrikhandwadi is prepared by further drying of shrikhand, it can be 
assumed that most of the organisms which are sensitive to drying process are killed, although their 
toxins may remain intact posing a threat to public health. Aerobic sporebearers are readily found 
in shrikhandwadi due to aerial contamination during packing and handling, which also contribute 
to the high level of coliforms. Organisms such as Salmonella sp. and spoilage organisms (including 
yeast and molds) can cause severe illnesses on consumption. 
 
iii) Lassi. Lassi derives its contamination mainly from dahi if it is not of good quality. Secondly, 
sugar and water also contribute to the microbial load. Use of nonpotable water can be a source of 
coliforms in lassi which can be further aggravated by the use of unclean utensils such as glasses 
during its mixing. Thus, aerobic sporeformers, yeasts and molds are found in high numbers in lassi 
sold at the shops of halwais or small vendors. Ice used in cooling lassi may also contribute to the 
load of coliforms. Lassi packed and sold at the organised dairies is subject to contamination during 
its manufacture in unclean vessels or by unhygienic handlers. Parts of water used during washing 
 63 
may remain in the utensils if the utensils are not carefully washed and dried. Such utensils may 
carry moist milky residues of dahi. The residues are a potent source of organisms like S.aureus 
which threaten to contaminate subsequent batches of lassi and consequently affect public health. 
Use of sterile packing materials such as polythene bags and clean filling and sealing machines 
could help to avoid the problems of contamination in the finished product. Leakages, improper 
temperature during transport and mishandling during storage, (improper storage temperature) may 
reduce the shelf life of the lassi. 
 
iv) Makkhan. Makkhan is an indigenous ‘butter’ prepared by small vendors, or is a household item 
and, therefore, the main source of its contamination is through low initial microbial quality of milk 
that is used in the preparation of dahi and faulty processing of milk. Relatively unhygienic vessels 
and stirrers (especially wooden) are difficult to sanitise fully. As such they are potent source of 
microbial contamination. Unhygienic practices adopted by the handlers, can facilitate transfer of 
microbes from their hands to the product while churning. Manual separation of butter from the 
whey / butter milk with hands or withunclean ladles also contributes to the bacterial load. 
Presence of molds indicates improper storage of makkhan before consumption. Absence of proper 
refrigeration facilities may cause rancidity and growth of other spoilage organisms which reduce 
the shelf life of makkhan. 
 
v) Ghee. Ghee is prepared by heating makkhan at 80-85°C. Most microorganisms are killed at 
this temperature but their heat stable toxins if any, may remain intact causing serious public health 
hazards. Immediately on preparation, ghee is relatively sterile. However it can get contaminated 
while packing or emptying into improperly cleaned jars or bottles especially during its sale by 
vendors as desi ghee. Contamination of commercial ghee can occur through leaking containers 
during transport or by use of unsterile containers. Occurrence of rancidity and off flavours in ghee 
is characteristic of microbial contamination. 
 
b) Paneer and channa. Milk stirred in unclean containers and used for preparation of either channa 
or paneer is an important source of contamination of these products. Contamination of channa and 
paneer with other aerobic spore formers occurs mainly through the aerial contamination in 
improperly ventilated and dusty rooms. Post preparation contamination occurs during packing and 
improper storage (without refrigeration) of the product. This leads to a build up an slime content 
 64 
due to presence of yeasts and other spoilage organisms altering the appearance and flavour of the 
product. Contaminated packing containers are also a source of bacterial and fungal contamination. 
 
c) Channa based sweets. Some of the channa based sweets include rusgulla, chum chum and 
rasmalai. Out of the three, rusgulla is sold in loose and packed forms. The other two sweets are 
available in loose form at halwai or sweetmeat shops. The quality of these sweets depends on the 
microbial quality of channa used in their preparation. Secondly, the handlers roll the channa into 
small balls or in different shapes with their palms. Careless handling of channa can contribute 
significantly to the (microbial) contamination of the sweets. Infected workers / carriers may also 
transmit the pathogens of typhoid fever, dysentry, tuberculosis etc. to the consumers through these 
sweets. Boiling of the products in sugar syrup does not kill most of the pathogens. Therefore, they 
remain a source of serious public health hazard. However, sugar syrup acts as a post preparation 
preservative and prevents the growth of most bacteria and molds, although when intrinsically 
present, they multiply and further increase microbial load causing defects and spoilage of the 
product. Storage of these sweets under refrigeration is a must to increase their shelf life. 
Temperatures beyond 10°C are detrimental to their flavour, shelf life and nutritive value. 
Colouring agents are also a source of contamination if good quality agents are not used. Solid milk 
and sugar residues may get accumulated in vessels used for the preparation and storage of sweet 
especially if they are not regularly cleaned and sanitized. The residues act as potent sites for the 
propagation of microorganisms. Use of unpotable water in preparation of sugar syrup leads to the 
build up of coliforms in the product on storage. Sweetened and condensed milk used in rasmalai 
(to dip the small balls on channa) should be free of microbial contamination. Therefore, it must be 
prepared from good quality milk and stored in clean and sanitised vessels prior to use. 
Contamination with aerobic sporebearers and molds may occur through air / envirnoment during 
cooling and refrigeration of the preparation. Flies and insects contribute in a big way to the load 
of spoilage as well as pathogenic microorganisms in unclean shops, where the sweets are not stored 
hygienically. Sweets being sold at open counters are frequently contaminated with dust and flies 
thus making them unsafe for consumption. Consumer awareness programmes may go a long way 
in ensuring that only quality sweets are sold at market places even though at higher prices. 
 
7. Condensed or concentrated milk products. 
a) Indigenous. i) Khoa and khoa based sweets, and ii) basundi, rabdi and khurchan.These items 
can get contaminated through the following sources 
 65 
 
i) Quality of milk. Since these products are predominantly made by halwais and rural folk, raw 
milk with heavy intial load of microorganisms is generally used for their preparation. The 
contaminations include heat resistant sporeforming microbes and enterotoxin producers especially 
S. aureus which survives the alternate heating and cooling processes. Secondly, heat coagulated 
proteins act as insulators and provide protection to the staphylococci against heat. 
 
ii) Production hygiene. Halwai shops in most cases process and handle milk and its sweets in 
unclean utensils, whereby micro-organisms like micrococci, bacilli, thermodurics and 
thermophiles find their way into these products. The usually unhygienic surroundings of halwai 
shops and production of these products in the open air makes them vulnerable to flies, soil and 
aerial contaminations. Pedha making involves a lot of handling wherein the khoa comes in direct 
contact with skin of the hands and hence high counts of staphylococci are are not unsual in pedha 
as compared to burfi or kalakand which is spread in trays and cut into pieces. Organisms causing 
typhoid fever and septic sore throat may be transmitted by way of carriers or active sufferers from 
the disease. 
 These problems can be managed by wearing gloves during the process of making pedhas 
and use of clean utensils and knives to cut the pieces of burfi or kalakand. 
 
iii) Effect of packaging. Khoa, burfi, pedha and kalakand are kept as such, or packed in materials 
like paper boxes, parchment papers, aluninium foils, polyethene bags, tins etc. On the other hand, 
rabdi, khurchan and basundi are kept open. In rural areas, khoa may be carried in a basket lined 
with tree leaves. In such cases contamination with yeasts, molds and sporebearing bacteria is 
inevitable. Packing in improperly cleaned and sanitised utensils may add to the contamination. 
Chemical treatment of different packing materials with antimicrobial agents has been shown to 
minimise microbial deterioration of the products. Packing in nitrogen atmosphere reduces 
microbial multiplication as against air packing. Hot packing is also found to be better than cold 
packing. 
 
iv) Effect of storage conditions. Khoa and its products are generally stored at ambient temperature 
and atmospheric humidity which favour the growth of microbes. The microbial count depends on 
the length of storage and the problem is further aggravated by moisture content of these products. 
Hence bacteria multiply and produce toxins which are harmful to human health. 
 66 
 Gulabjamun is safer from microbiological point of view due to its spongy nature which 
facilitates soaking of sugar syrup. Rabdi, khurchan and basundi are simmered and not boiled and, 
therefore, survival of heat-resistant microbes i.e., sporeformers can be expected. The organisms 
gain entry through aerial contamination as well as from unclean utensils. On account of high 
moisture content molds are generally encountered in these products. In case of basundi, the 
organisms can also gain entry through basundi mixes which generally have high yeast and mold 
as well as bacterial counts. Proper packaging under hygienic conditions can enhance the shelf life 
of basundi. Hence packaging coupled with hygienic preparation and handling of these products 
can increase their shelf life and at the same time render these products safe for human consumption. 
b) Commercially available sweetened condensed milk. 
i) Quality of raw materials. The raw milk used in the production of sweetened condensed milkshould be of manufacturing grade with methylene blue reduction test > 3.5 hours, resazurzin 
reduction test > 5.5 in hours and Direct microscopic count -<106/ml. There should be no physical 
abnormalities such as flakes,clots and blood in milk, no abnormal flavour or odour and the milk 
should have low spore count. 
 
ii) Sugar. It should not contain osmophilic yeasts, molds and bacteria producing acid and gas. 
Sugar should be stored in a dry place which is free of dust, insects and rodents. When sugar is 
exposed to high humidity in an unsanitary room, it may become moldy. As such, it should be 
handled carefully to avoid contamination. 
 
iii) Skim milk powder. The powder used for standardisation of milk before condensing 
occassionally has high counts of heat resistant streptococci and micrococci. Their numbers can be 
reduced by subjecting skim milk to high temperature which may in turn denature the proteins with 
the development of viscocity. 
 
iv) Processing time and temperature conditions. Processing of standardised milk into a 
condensed product is divided into the following steps. Microbial contamination of the product can 
occur at many of the following stages : 
 
a) Preheat treatment. Milk is heat treated at a temperature of 82-100°C for 82-30 minutes, which 
destroys all spoilage and pathogenic microbes. However, heat resistant proteases and lipases 
produced during the growth of micro-organisms remain intact. Care must be taken to ensure that 
 67 
the product does not get deprived of full heat treatment because of leaky valves, dead ends and 
other manufacturing defects. 
 
b) Holding in the hot well. The development in viscocity of SCM depends on the temperature and 
time of holding of the preheated milk. The total count, however, does not show drastic reduction 
as preheat treatment destroys all the heat labile organisms. Only the sporeformers and micrococci 
are liable to survive at this stage. 
 
c) Addition of sugar. A 65% concentrated syrup is added by vacuum near the end of the 
condensing process. The sugar results in the plasmolysis of organisms present in milk drawn to 
the vacuum pan. However, sugar should not be added before preheating the milk because it 
increases the resistance of organisms. 
 
d) Superheating. Superheating of milk to 70°C, has little effect on the bacteriological quality of 
the product . 
 
e) Condensing. In the condensing operation, milk and sugar mixture is subjected to vacuum 
evaporation in a pan at 57.2°C for 3-4 hours. The vacuum pan may sometimes become a source of 
contamination of the product. It should, therefore, be sanitised properly. The sticky nature of the 
product increases the difficulty in cleaning and “cooked on” material may also become a potential 
source of problem. The milk stone can be removed by acid and alkali treatment. Vacuum pan heads 
should also be cleaned properly. A solution of chlorine may be used to sterilise the cleaned vacuum 
pans. 
 
f) Finishing and seeding. When condensation is complete, vacuum in the pan is broken, the 
process being called finishing. Some manufacturers adjust the composition of milk by adding 
sterile water or undercondensed milk which may enhance the chances of post- contamination. A 
better procedure would be to adjust the composition of standardized milk and suitably alter the 
finishing of batch mixes. 
 Seeding is the process of providing nuclei for the development of lactose crystals. Seeding 
can be done by adding sterilised lactose or good quality condensed milk from a previous batch. 
The seed should be bacteriologically safe and lactose should be presterilised before seeding at 
30°C. 
 68 
 
g) Compositional variations. The concentration of sugar should vary from 60 to 63%. When 
sugar concentration drops below this level microbial growth tends to increase. Pockets in the 
pipelines and equipment which have accumulated water on storage can dilute the product and also 
provide a micro-environment conducive to the growth of microorganisms. Flushing pipelines and 
discarding the first flow through pipes would avoid such problems. 
 
h) Sterility of cans. Cans used for filling SCM should be sterilised before use otherwise they may 
contribute to the contamination. Lids should also be properly sterilised before use. Cans should 
be regularly examined for microbiological quality by rinse method. The cans must be filled as full 
as possible to minimise head space otherwise aerobic organisms, if any, may grow and cause defect 
in the product. Imperfect seals or can damage may also permit the entry of organisms and air which 
favours the growth of microorganisms. 
 
i) Sterility of equipment. The equipment should be sterilised by use of chlorine, steam or other 
suitable sterilants. The pipelines, filling machines should be thoroughly washed, cleaned and 
sterilised. The sterility of equipment can be checked by means of swab or rinse method. Gaskets 
and valves are major hazards. Gaskets should be dislodged from the sockets, cleaned and immersed 
in a sterilant. Valves often form blind pockets. The accumulated residue of the SCM lies in the 
seat of the valve and gets dislodged when moved and comes in contact with the product. Care 
should be taken to see that valves and fittings satisfy all the requirements of hygienic maintenance. 
 
j) Storage conditions. The keeping quality of SCM is dependant on the concentration of sugar, 
total solids and the extent of destruction of organisms. The plasmolysing action of the ingredients 
effectively checks the growth and proliferation of microorganisms. Therefore, the shelf life of 
SCM is long even at ambient temperature (at which most organisms grow). If SCM lacks sterility, 
micrococci and molds may proliferate producing acidity and proteolysis causing a gradual decline 
of quality on storage. 
 
c) Evaporated milk. Evaporated milk has a longer shelf life than pasteurised fluid milk / raw milk 
because of sterilisation effect. However, if the initial quality of milk is not good, ie., contaminated 
with sporeformers which survive sterilisation the shelf life of the product is adversely affected. 
 69 
Some of the common factors contributing to the inferior microbiological quality of this product 
are: 
i) Quality of raw milk. Raw milk is cooled immediately on receipt to retard the growth of 
contaminants. Hence temperature of raw milk held in the plant should be preferably below 4°C. 
The milk should not be held for more than 24 hrs. and quality control tests should be carried out 
before processing. 
ii) Standardisation. Raw milk is frequently clarified before being diverted for processing. 
Standardisation of milk with cream or skim milk may add to the contamination if, they are of 
inferior quality, thereby further deteriorating the microbiological quality of the finished product. 
 
iii) Heat treatment. Pathogenic nonsporulating bacteria are destroyed during this process. 
However, faulty heat treatment may leave residues of surviving bacteria which may bring about 
spoilage of the product, subsequently. The heat treatment however, does not inactivate preformed 
enterotoxins of S. aureus which may be carried over to the finished product posing a serious public 
health hazard. 
 
iv) Condensing operation. Usually done at a temperature of 54.5°C. Although bacteria are 
destroyed at this temperature, the thermophilic bacteria grow under these conditions and bring 
about subsequent spoilage of the product. 
 
v) Homogenisation. After homogenisation, the product is cooled immediately and stored until 
further processing. Therefore, holding under good refrigeration conditions until packing and 
sterilisation is important because the product is not yet sterile. 
 
vi) Sterilisation and packaging. The product is subjected to sterilisation before packaging to 
avoid contaminants. Someof the sources of product contamination during sterilisation are as 
follows : 
 
a) Filters. The filters used for sterilizing the milk in the final container are complex and difficult 
to clean properly. Therefore, filters should be dismantled, cleaned with detergent and sanitiser 
solutions which are microbicidal. 
 
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b) Cans and packing containers. The cans should be filled with a head space to allow room for 
expansion during sterilisation. Otherwise leakage occurs, and bacteria can enter the can when 
temperature is not enough to cause their destruction. The can must be hermetically sealed and 
leakage detected before and after sterilisation. In order to have adequate keeping quality at room 
temperature, evaporated milk should be completely sterile. UHT treatment with aseptic packaging 
is ideal. Recommended treatments are 130°C for 30 secs. or 150°C for one sec. These schedules 
are satisfactory to destroy mesophilic bacteria including sporeformers. The containers and the lid 
of the packaging set may also be a source of contamination along with air. Presterile containers 
(sterilised with H2O2) should be used which are then hermetically sealed. 
 
 
8. Cereal based milk products.: 
a. Indigenous sweets. Kheer, falooda, plain and kesar phirni and kaju katli are relished by people 
in most urban cities. They are prepared by halwais or various refreshment outlets. The raw milk 
itself is of variable microbial quality as handling of milk by vendors and halwais is not always 
hygienic. The utensils used for preparation are not always cleaned and sanitised adding to the load 
of coliforms and spore formers. Potable water is also not always used. Cereals like rice, sabudana 
and maida used in their preparation may not be of good microbiological quality and may add on 
to yeast and mold contamination. The products except falooda which is prepared fresh, are 
generally stored in the open at smaller outlets exposing them to aerial contamination. At larger 
outlets (organised shops) they are stored under refrigerated conditions and, therefore, the quality 
is better. The preparation of falooda requires sugar syrup which may also be contaminated with 
microorganisms. Phirni and kheer, have a high moisture content and hence are more prone to 
contamination with molds if not stored properly. Recycling of old kaju katli into the fresh product 
not only increases its microbial load but also the amount of heat stable toxins produced in it which 
pose a serious public health threat to consumers e.g., enterotoxins of S.aureus. 
 
b. Dried milk. The categories of milk included in this group are : skim milk powder, infant foods 
and malted milk. Their microbiological quality depends on the following factors : 
 
i) Quality of raw milk. Raw milk should be fresh and of very high microbiological quality. It 
should be free of heavy metals and acidity. The milk should also be free of thermoduric bacteria, 
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since the quality of dried milk is dependent on these organisms, especially thermophilic organisms 
which can grow during the processing operations. 
 
 ii) Clarification/Filtration. This step may be omitted since it may cause removal of fat along 
with extraneous matter, and the plate count may become higher due to disintegration of bacterial 
clumps. The clarifier itself should be cleaned and sanitised. It should be made free of residues and 
slime with the help of hot water and detergent. Discs should be removed, cleaned and dried. 
 
iii) Separation. A centrifugal seperator is used for the preparation of skim milk. It reduces 
bacterial load by trapping the organisms in the slime. Therefore, it is necessary that separators are 
kept cleaned and sanitised. 
 
iv) Standardisation. This step may contribute additional microflora to milk because of additives 
like whole milk or skim milk. 
 
v) Homogenisation. This step is carried out to uniformly distribute the fat in whole milk powder 
and facilitate reconstitution of dried milk to fluid milk. There may be an increase in plate count 
due to breaking up of bacterial clumps or from contaminated cooling water past the pistons of the 
homogeniser. This can be monitored by any significant changes in microflora from milk taken 
previously in the run. Therefore, the homogeniser should be properly cleaned and sterilised. 
 
vi) Processing of milk. The following steps are employed for the processing of milk : 
a) Preheating.: Most bacteria except heat resistant forms are destroyed at 95°C in 10-30 mins. 
Preheating also reduces the thermoduric count. Micrococci and microbacteria predominate when 
preheating is done at a lower temperature. Hence good sanitation measures are essential to reduce 
the microbial load. 
 
b) Concentration. There is little chance of microbial contamination by spray drying, as air at high 
temperature is used for preheating of milk and preconcentration is brought about in vaccum pans 
or evaporators. In roller drying, milk is concentrated before it is fed to the dryer. In both cases, 
evaporators should be cleaned properly and operated under high standards of hygiene. 
Carelessness at this stage may cause increase in thermophilic or thermoduric counts. Application 
of UHT leads to the production of powders of high microbiological quality and, therefore, 
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cleanliness of these complex evaporators is of considerable imporance. The crucial points in this 
regard are return loops, blank ends, feed control valves and vapour ducts. Built in CIP installation 
ensures thorough cleanliness. 
 
c) Drying. The operation involves the following : 
i) Feed tank. The concentrated milk can be directly fed to dryers, although feed tanks (also called 
as balance tanks) are frequently used. The tanks may pose a microbiological hazard as they 
provide optimum temperature for the growth of microbes which may lead to a build up of 
contaminants. Enterotoxin producing staphylococci which cause food poisoning outbreaks are of 
particular interest in this regard. Presence of high amounts of high total solids tend to form sludge, 
which can contaminate a fresh lot. Mesophilic bacteria and pathogens grow efficiently at this stage. 
Precautions to be taken include retention of covers on the tanks and a low level of milk. 
ii) Dryers. 
a) Spray drying. Drying causes instant death of a majority of microbes when milk comes in contact 
with the hot dry incoming air. Microbes that survive die slowly as a result of oxidative changes. 
Microbial survival may be due to a protective layer produced by milk solids or by the cooling 
effect during evaporation. In due course microbial density may reach a high proportion in the 
product. 
 The walls of the drying chamber should be kept clean and free of any residual product build 
up. 
 
b) Roller drying. The concentrated milk from feeder tank is fed to a roller dryer where the high 
temperature of 100-148°C destroys bacteria but the interior of the hood used for removal of vapour 
from the dryer can still harbour microorganisms due to high humidity. The drums reduce the viable 
microbes and hence powders prepared by roller drying contain lower number of microorganisms 
than spray dried powders. The thermoduric bacteria and aerobic sporeformers may predominate in 
this type of powder due to manual contact during recovery. Sterile disposable hand gloves or 
mechanical means should be used for ensuring high quality of the product. 
 
c) Instantization. It is the process of forming agglomerates of powder to improve wetting and 
dispersing properties, which may increase microbiological hazards. 
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d) Packaging. Dried milks are hygroscopic. Therefore, packing should be done in an atmosphere 
of inert gas, since moisture increases the load of contaminants. 
 
e) Storage. Powders should be stored in a dark, cool place at temperatures below 24°C