The milk will be converted into fermented milk and finally into curd. The process is called lactic acid fermentation. During this process, the microorganisms such as Lactobacillus, Pediococcus, Streptococcus and other commonly called lactic acid bacteria (LAB)  convert Lactose (Carbohydrates) into lactic acid by fermentation and coagulate milk protein (Casein) to produce a homogenous curd.
Carbohydrate \(\underrightarrow { LAB } \)  Lactic acid + CO₂
The products of fermented milk are Dahi, Lassi, Buttermilk, Shrikhand, etc. These products have originated from India.

The name of gobar gas (or biogas) is methane.It is generated by the activity of methanogenic bacteria (i.e., methane producing anaerobic bacteria). Following are advantages of using methane as a source of energy:
(i) Methane is insoluble and therefore, separates very easily from the fermentor.
(ii) It can be very easily pressurized or liquefied for storage
(iii) It is readily combustible.

Setting up of a gobar gas plant or biogas plant.

Certain bacteria and cyanobacteria are nitrogen fixers.They convert atmospheric free nitrogen into ammonium form which is easily assimilated by higher plants.Thus, these microorganisms increase the fertility of soil without causing any environmental harzards and therefore, called biofertilizers.Example - Rhizobium and Anabaena.   

(i) Rhizobium leguminasorium
(ii) Anabaena forms symbiotic association with Azolla (an aquatic fern)
(iii) Saccharomyces cerevisiae (Yeast)
(iv) Methanobacterium