- Butter
The fat content of butter is generally about 80 per cent. The non-fat components of butter consist of moisture, milk solids not fat and salt if added. Most of the butter produced in our country is converted to ghee.
Butter is made from sweet or sour cream. The cream is pasteurised at 62.8oC for 30 minutes after which it is immediately cooled. Then a culture of desirable micro-organisms is added. The culture consists of bacteria of two types. Streptococcus cremoris or lactobacillus lactis ferments lactose producing lactic acid which in turn curdles the milk. Leuconostic citrovorum principally attacks the citric acid of milk-producing volatile acids and products such as diacetyl which give the desirable flavour and aroma to the butter. The cream is then allowed to ripen at 21.1o C for several hours for the fermentation to take place.
The ripened cream or dahi is next churned. Churning brings about the denaturation, by violent agitation of the fat globule surface; the membrane material is eliminated in buttermilk. The fat globules clump together causing a change from an oil-in-water emulsion to a water-in-oil emulsion . For this change to be effective the temperature should be such that there is a blending of solid and liquid fat. As churning proceeds the cream becomes granular and a definite separation of the butter milk takes place.
The colour of the butter varies from yellowish white to deep yellow. Yellow colour is due to carotene derived from the feed of the animal. Sometimes synthetic permitted carotene is added. Pasteurised table butter should be stored at 80°F to maintain good quality and prevent deterioration. When butter spoils as a result of hydrolysis of triglyceride molecules, the disagreeable odour and flavour are due primarily to the release of free butyric and caproic acids from the triglyceride molecules.
- Cheese
Commercially sometimes curdling is done using rennet berries. Cottage cheese is called paneer. Cottage cheese is made using curd for curdling milk and removing the whey with weight. It does not undergo any further processing. It is highly perishable and must be kept refrigerated. Recipes like peas and paneer curry are made from cottage cheese.The varieties of cheese are differentiated according to their flavour, body and the texture which in turn depends upon the type of the milk used, manufacturing and processing method adopted salts and sweetenings added and the type of bacteria and mould species used in the ripening. Cheese is classified as hard or soft, depending on their moisture content and whether they are ripened by bacteria or moulds or unripened. Cheese is made of casein.
Figure gives classification of cheese.
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- Curd formation
Pasteurised whole milk is brought to a temparature of 31oC and lactic acid producing starter culture and required colouring matter are added. After about 30 minutes to the mildly acidic milk, rennin solution is added, stirred and allowed to set the curd for 30 minutes.
- Curd
This is India's most commonly used milk product and 7 per cent of milk produced is used for curd.
Nutritive value almost remains the same during curd making. The digestibility is better when compared to ordinary milk. Calcium and phosphorus content of curds are more easily assimilated. Curds contain more B vitamins than milk.
During curd formation the lactose of milk is converted into lactic acid. Acid curdles the milk protein. The fat globules coalesce and distribute themselves on the top. Organisms involved in curd formation belong to the group of lacto bacillus and streptococcus -L. Casei, L. brevis, L. bulgaris, S. Lactis and S. Thermophilus. Starter culture containing a combination of lacto bacillus bulgaris and streptococcus, organisms is good. Starters containing yeasts, moulds and gas-containing organisms spoil the quality of curd. Curd is prepared by initially boiling the milk to destroy viable organisms. It is cooled to the body temperature and starter, 10 ml per litre, is added. Lesser quantities are needed during summer. After 6-8 hours an acidity of 0.9-1 per cent acid is formed. Due the drop in pH, the casein is coagulated and the curd is set. Curd is enjoyed as such and also used in the preparation of kadhi, raihta, lassi and shrikhand.
- Yogurt
Yogurt is a type of curd. Whole, low-fat and skim milks and even cream can be used to make yogurt. Often, non-fat dry milk solids are added. There is increase in folic acid concentration during the fermentation process. In the production of yogurt, a mixed culture of lactobacillus bulgaricus and streptococcus thermophilus, lactobacillus acidophilus is usually added to the pasteurised milk and incubated at 42 to 46°C. Often, yogurt is marketed with sweetened fruit added. Yogurt can be used in lactose intolerance. The fermentation lowers the lactose content by 20-30 per cent.
By churning curd and removing butter, butter milk is obtained. It is used as a beverage for quenching thirst. Powdered butter milk can be made by spray drying. Metchnikoff postulated that the bacteria involved in yogurt fermentation, lactobacillus bulgaricus and streptococcus thermophilus suppress the putrefactive type fermentation of intestinal flora. Fermented milk has been reported to be useful for a wide variety of disorders like colitis, constipation, diarrhoea, gastroenteritis, diabetes and hypercholesteremia.
- Shrikhand
It is another fermented product which is made by concentrating dahi by removing whey and to which sugar, flavour and condiments are added.
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