Yeast Production

the production of bakers’ yeast, based on the reproduction of yeasts in liquid nutrient media prepared from molasses (a by-product of sugar manufacture).

Molasses is diluted with water (in the ratio 1:4), treated with bleaching powder to disinfect it, and acidified with sulfuric acid; after nutrient salts containing nitrogen and phosphorus are added, the mixture is heated to boiling and, after precipitation of the colloids (in ten to 12 hours), it is decanted (poured off the sediment) and a transparent solution is filtered out. Yeasts reproduce in several stages and in each succeeding one the size of the yeast mass increases severalfold. Yeasts accumulated in a laboratory by the cultivation of pure cultures on malt wort then go to a pure cultures section, from which the yeast mass enters a yeast-growing apparatus to produce mother yeasts. The concentration of nutrients in the fermented medium is regulated by the entry of wort. The inflow of molasses wort and nutrient salts varies from seven to ten hours. Air is forced through an air-distributing system on the bottom of the yeast-growing apparatus (60-80 cu m per hour for 1 cu m of liquid, depending on the stage of yeast accumulation). Cold water is passed through coils in the apparatus in order to keep the medium at an optimum temperature. The process of growing commercial yeasts takes 12 hours.

Yeasts are isolated from fermented wort by separators with a capacity of 12-20 cu m per hour. The resulting thick yeast cream is diluted with cold water and separated again. The moisture from the yeast concentrate is removed by filter presses or vacuum filters. The pressed yeasts are mixed in a mixer until the mass is homogeneous and then shaped in a molding machine into 50, 100, and 1000 g bars. The packages of yeast are wrapped in paper in an automatic machine, packed in boxes, and then chilled in a refrigerator to -2°C.