A process for production of ethanol using activated stable yeast crystals in a modified conventional batch reactor, said process comprising mixing stable yeast crystals to a low strength molasses solution having specific gravity in the range of 1.030 to 1.060 and incubating the stable yeast crystals therein to obtain activated stable yeast crystals, separating the activated stable yeast crystals, converting the low strength molasses solution into a molasses fermentation broth of a specific gravity in the range of 1.09 to 1.1 in a modified fermentation vessel fitting with a low speed mechanical stirrer, estimating the initial sugar concentration in the fermentation broth, adding the activated stable yeast crystals to the above fermentation broth in the range of 0.5 to 2.0% W/V and fermenting the mixture, terminating the fermentation when the specific gravity of the fermentation broth reaches a range of 1.014-1.045, separating the activated yeast crystals from fermented broth and recovering the ethanol from fermentation broth.