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The use of phenolic protein precipitates (trub) from beer production in animal feed
Ru, W. und Meyer-Pittroff

Modern beer production is a highly refined biological and mechanical process. The brewing and fermentation process can be summarized as follows: Malt (sprouted and dried grain) is milled and water is added. Facilitated by the malt's own enzymes, a portion of the malt solids are solubilized and extracted. After the extraction process, the spent grains (cracked and rinsed malt grist) are separated from the wort (liquid malt extract, a solution of sugars and proteins) by means of lautering. Hops are added to the wort while it is boiling. A fraction of the dissolved protein in the wort is coagulated during the boil. This substance, known as the hot break material or hot trub, precipitates out and is removed with the spent hops by means of a separation system using gravity. The wort is then cooled to a temperature between 0-8 ?C. Through the cooling of the wort, the phenolic compounds derived from the hops precipitate out with the proteins through the reduction in temperature [1]. This is known as cold break material or cool trub and is separated from the wort by means of flotation or filtration. The yeast is then added to the wort and transferred to fermentation tanks. At the beginning of fermentation, the yeast cells multiply rapidly. After fermentation is finished, the young beer is separated from the yeast no longer in solution and then transferred to lager tanks for ageing. A part of this yeast will be reused in the brewery, however the "spent yeast" or "old yeast" s collected at this point for later disposal. As the beer ages, small amounts of yeast fall out of solution and accumulate at the bottom of the lager tank. The proteins and hop substances contained in the sediment are considered to be impurities in the finished beer. At the end of the lagering period, the beer is usually filtered and ready for packaging. Spent yeast is routinely used in animal feed, and in order to eliminate the threat of potential pathogens and to improve its nutritional value, the yeast is heat-treated. This process lyses the cells and is achieved by heating to a minimum of 90?C, often in conjunction with a process intended to concentrate or dry the yeast. Alternatively, the yeast can be stabilized with propionic acid.

Descriptors: Brauereiabflle, Trocknung, Trub

Monatsschrift fr Brauwissenschaft 56, Nr. 5/6, 84-88, 2003