The strain chosen for compressed yeast and the growth conditions tend to favor high activity in both lean and sweet dough. The water content of the yeast cream is reduced by passing the yeast cream through a rotary vacuum filtration unit. The pressed cake is extruded through a rectangular nozzle and cut into the proper length and weight. It is highly perishable and must be stored at a low temperature to prevent excessive loss of activity. Compressed yeast generally has a shelf life of approximately four weeks from packaging date when kept under refrigerated conditions. Compressed yeast contains about 70 percent water and 30 percent yeast solids. Of the yeast solids, about 46 percent is protein, 45 percent is carbohydrate, and the rest is fat and ash. The solids content can go up to 34 percent. Higher yeast solids give higher activity. Higher growth rates give higher protein, higher activity, lower carbohydrate, and lower stability. Lower growth rates give lower protein, lower activity, higher carbohydrate, and higher stability. Fresh yeast may range in color from dark brown to almost white, and in texture from easy to crumble to sticky. Appearance is affected by strain, molasses source and type, fermentation conditions, moisture level, and product age. Low fermentation pH gives darker yeast. Emulsifiers give lighter color and frozen storage gives softer texture, but neither affects performance. High moisture makes yeast darker. Storage time, temperature, and oxygen make yeast darker and stickier and reduce its performance. Old or spoiled yeast frequently appears dark and sticky, but, appearance alone is not a dependable guide of yeast quality.