METHOD OF MANUFACTURE OF YOGHURT(YOGURT)

Starter culture for yoghurt (Yogurt)

Two microorganisms namely, Lactobacillus bulgaricus and Streptococcus thermophilus, growing together symbiotically, are responsible for the lactic fermentation of the yoghurt. In some countries, apart from these two bacteria, the culture also contains lactose fermenting yeasts, Leuconostoc strains, Lactococcus lactis subsp. lactis biovar diacetylactis and Lactobacillus acidophilus.The method of maintaining purity of the yoghurt culture is very important and it is better to maintain the mother cultures individually rather than in mixed form.

The optimum pH and temperature for growth of Streptococcus thermophilus is 6.8 and 38°C. These strains usually reach acidities of 0.80 to 0.95 per cent. In case of Lactobacillus bulgaricus, the optimum temperature for growth is 42°C and the acidity obtained is 1.25 to 1.50 per cent.

The extreme sensitivity of both these microorganisms to antibiotics especially, penicillin, calls for selection of milk intended for yoghurt manufacture to be free from residual penicilin. More over, extra care has to be exercised in maintaining the purity of the yoghurt cultures since they can be easily overgrown by contaminating organisms.

Traditional method of yoghurt making

The milk is evaporated to 1/3 to 1/4 water content so that it attains the required concentration. Alternatively, 4-5% non-fat dried milk (NFDM) can be added to the whole milk.

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

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

The product is chilled to 5°C. Further acidity of 0.9% lactic acid may develop while the product is being chilled.

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

Industrial Method of Yoghurt Making

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

Then it is cooled to 45-48°C.

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

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

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

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

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

Flavoured yogurt

The flavoured yoghurt has gained popularity in recent years. Three types of flavours viz. artificial, natural with artificial flavours mixed and natural fruits are commonly used. These flavours may be added to the milk intended for preparing yoghurt by mix blending, fruit on bottom and bulk mixing.

Flavoured yoghurt has definitely an edge over the plain yoghurt in that the high acidity encountered in the product less pronounced and suppression of objectionable off flavours and the need to concentrate the milk is eliminated.