In India, milk is being used for producing milk products using lactic acid-producing bacteria. Curd is similar to yoghurt. In several other parts of the world, milk products have been prepared by using yeasts and lactic acid-producing bacteria. The yoghurt is popular in eastern European countries, koumiss in central Asia, and leben in Egypt. There are several other milk products such as butter, butter milk, cheese, etc. In most of them lactobacilli are used that ferment the milk. The usual method of producing curd on large-scale production is through addition of the Lactobacillus bulgaricus to pasteurised milk. Most common curd production is tracing inoculum from previous batch to prepare the curd by fermenting the milk. The preparation of Gram-stain slides helps in determining the types of microorganisms for curd preparation.
- Pasteurised milk
- Mix pasteurised milk in water in a ratio of 1:25 (v/v).
- Boil this mixture and cool at 45ºC.
- After cooling the milk, inoculate it with a little amount of curd.
- Incubate the inoculated milk at 45ºC for about 8-12 hours.
- Adopt similar procedure in case of raw milk. The use of commercial certified curd is a bette source of inoculum because the product contains the live or viable culture which can be further confirmed by negative staining.
- After the process is over, examine the colour, aroma, texture and taste.
Record observations after making the negative stained preparation of the smear from freshly prepared curd.
Dr. R. C. Dubey – Practical Microbiology