Graduate Thesis Or Dissertation
 

Studies on control of diacetyl off-flavor in beer

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/kw52jd05s

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  • Sporadic outbreaks of diacetyl off-flavor in beer are a serious economic problem to the brewing industry. Studies were carried out in an attempt to improve the understanding of the problem and to experiment with new ways of controlling this defect. The Owades and Jakovac method of diacetyl determination as modified by Pack was further refined to increase its sensitivity to the low diacetyl levels encountered in beers. A survey of alcoholic beverages showed diacetyl levels of all samples tested to be below threshold levels for organoleptic detection. Comparing yeast strains on a per cell basis, a 2.5-fold difference was found to exist between yeast strains in their ability to produce diacetyl. Also, corn steep liquor addition to wort resulted in increased diacetyl production during the subsequent fermentation. Diacetyl removal from beer was studied using both live whole cells and crude enzyme extracts. Cells of Streptococcus diacetilactis 18-16 destroyed diacetyl from solutions at a rate almost equal to that achieved by the addition of live, whole yeast cells. Yeast cells impregnated in a diatomaceous earth filter bed were found capable of destroying all of the diacetyl from solutions percolated through the bed. Undialyzed crude enzyme extracts from yeast cells removed diacetyl very slowly from beer at its normal pH. When attempted at a pH of 5.0 or higher, rapid diacetyl removal was achieved. Dialyzed crude enzyme extracts from yeast cells were found to destroy diacetyl in a manner quite similar to that of diacetyl reductase from Aerobacter aerogenes, and both the bacterial extract and the yeast extract were stimulated significantly by the addition of NADH. Diacetyl reductase was studied, and it was found that at least three strains of A. aerogenes were better sources of the enzyme than strain 8724, the strain generally studied. Gel electrophoresis results indicated that at least three different NADH oxidases were present in crude extracts of diacetyl reductase. Sephadex gel filtration was found to be an excellent method for separating NADH oxidase activity from diacetyl reductase activity. It was also noted that alcohol concentrations approximately equivalent to that found in beer were quite inhibitory to diacetyl reductase activity.
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