Micro-organisms such as Lactobacillus and others commonly called lactic acid bacteria $(LAB)$ grow in milk and convert it to curd. During growth, the $LAB$ produce acids that coagulate and partially digest the milk proteins. A small amount of curd added to the fresh milk as inoculum or starter contain millions of $LAB$, which at suitable temperatures multiply, thus converting milk to curd, which also improves its nutritional quality by increasing vitamin $B_{12}$. In our stomach too, the $LAB$ play very beneficial role in checking diseasecausing microbes.