Centrifugal separation, isolation and characteristics of brewery spent grains and press liquor.

Stiles, S.R. and Hebert, H.S.

Abstract
The brewing industry processes a significant portion of the world's cereals, converting the starch but largely discarding the remainder as spent grains at prices well below its cost value. Thus, 25 to 30% of the raw material, containing valuable protein (equivalent in dietary value to soya protein concentrate) and cereal oil, which could be recovered for human consumption, is used for cattle feed. Centrifugal equipment manufacturers have improved the separation capabilities of their machines and centrifugal lautering does not require the presence of fibres to create a filter bed as in conventional lautering. Finely ground grists can therefore be used to obtain high conversion yields. Brewers' protein and cereal oil can then be isolated as valuable by-products. During mashing, part of the proteinaceous membrane surrounding starch granules is dissolved to form part of the soluble extract. The remainder appears as small insoluble particles mixed with fibre and cereal oil in the spent grains. The protein is nutritious and digestible. Cereal oil must be completely absorbed on and rejected with the spent grains or beer quality is impaired. It is a mixture of mono and diglycerides, free fatty acids, and saturated and unsaturated fatty acid esters. An economic projection for a 1 million US barrel brewery is shown in which centrifugal lautering and separation of by-products is compared with conventional lauter tun and filter press operations and wet spent grains disposal. Part of the advantages of the centrifugal system results from improved brewhouse yield, due to better conversion and lower retention of extract, and part from the upgrading of the low value spent grains to dried, deoiled brewers protein, cereal (cooking) oil and cellulose fibre.
Keywords: brewing by-product centrifugation composition mashing particle size protein spent grains