Starter culture for yogurt

Two microorganisms viz. Lactobacillus bulgaricus and Streptococcus thermophilus, which grow together symbiotically, are responsible for the lactic fermentation of yogurt. In some countries, in addition to these two bacteria, the culture also contains lactose-fermenting yeasts, Leuconostoc are, Lactococcus lactis subsp. lactis biovar diacetylactis and Lactobacillus acidophilusThe method of maintaining the purity of the yogurt culture is very important and it is better to keep the stock cultures individually rather than in a mixed form.

The optimum pH and temperature for the growth of Streptococcus thermophilus It is 6.8 and 38 ° C. These strains usually reach acidity of 0.80 to 0.95 percent. In case of Lactobacillus bulgaricus, the optimum growth temperature is 42 ° C and the acidity obtained is 1.25 to 1.50 percent. The extreme sensitivity of these two microorganisms to antibiotics, especially penicillin, requires that the selection of milk for the manufacture of yogurt be free of residual penicillin. In addition, special care must be taken to maintain the purity of yogurt cultures, as they can easily be covered by contaminating organisms.

Traditional method of making yogurt

The milk is evaporated to 1/3 to 1/4 water content to bring it to the required concentration. Alternatively, 4-5% skimmed milk powder (NFDM) can be added to whole milk.

Heat at 82-93 ° C for 30 minutes. It is then cooled to 42-43 ° C and inoculated with 2-3% starter culture (Lactobacillus bulgaricus and Streptococcus thermophilus).

The milk is then incubated at 42-43 ° C for 3 hours or until a titratable acidity of 0.75% lactic acid or coagulation occurs.

The product is cooled to 5 ° C. Further 0.9% lactic acid acidity can develop as the product cools.

The product can be satisfactorily stored for 1-2 weeks at 5 ° C.

Industrial method of making yogurt

The desired quantity of milk is weighed and heated at 80-90 ° C for 15-20 minutes.

Then it is cooled to 45-48 ° C.

Two to three percent of the yogurt culture is added to the milk and mixed well.

The milk is kept in clean, sterilized containers for setting.

The milk in the container is incubated at 45 ° C until coagulation is firmer.

The product is removed from the incubator and kept at 5 ° C until it is distributed to consumers.

The equipment is cleaned and kept ready for the next batch of operation.

Flavored yogurt

Flavored yogurt has gained popularity in recent years. Three kinds of flavors viz. Artificial, natural fruits with mixed and natural artificial flavors are commonly used. These flavors can be added to milk for yogurt by blending, bottoming fruit, and bulk mixing.

Flavored yogurt definitely has an advantage over plain yogurt in that the high acidity found in the product is less pronounced and the suppression of off-flavors and the need to concentrate the milk is eliminated.

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