Disposal of brewing effluents and surplus yeast with spent grains.

Hawley, J.S.

Abstract
Spent grains from the lauter tuns are moved by blowers or screw conveyor to screw presses which reduce the moisture content to 68% so that these grains can go to the mixing conveyor where other materials are added before drying. The expressed solution is mixed with residual wort from the lauter tuns and centrifuged to give a product of S.G. 1033 with 6.75% total solids which is fed to the evaporators. Surplus yeast is centrifuged to a 50% (v/v) suspension of yeast which is autolysed at 150 degrees F and fed to the mixing conveyor. Hot wort drainage with suspended trub is mixed with grains as discharged from the lauter tuns and processed with them as above. Liquid discharge from the various centrifuges is evaporated in six stages by spraying over hot tubes to give a solution of S.G. 1089. The removal of suspended matter by centrifugation before evaporation prevents fouling of the heated tubes. This concentrated solution is fed with the centrifuge solids and autolysed yeast to the mixing conveyor where a proportion of previously dried grains is recycled to provide a homogeneous mixture to feed to the grains driers, although a part is drawn off for disposal as wet grains. The mixture from the mixing conveyor is fed to the wet grains driers where furnace gases are kept below 1200 degrees F to prevent fire. The hot grains are cooled by blowing washed air through them, a proportion is removed for recycling at the mixing conveyor and the final product is transferred to dry grains storage bins. At its maximum capacity the plant produces 5,000 lb/h of dried grains.
Keywords: brewing effluent by-product yeast