<p>This invention belongs to the field of food industry. In order to complex apply of grains being resolved on the producing alcohol the starch being comprised in grain or in grain processing products is isolated in form of oligosaccharide. With a said view there is hydrolysed starch without isolation of the processing products. The hydrolysis process is realised in water suspension (1: 200 to 1: 600) using thermostable amylolytic enzyme. The enzymes are used in amount of 300000 to 600000 international units per kg of raw material at a reaction temperature of about 90 5 0C.</p>