The significance of oxygen over the course of the different stages of beer production varies:
If oxygen enters the process during mashing and wort handling, unsaturated fatty acids can become oxidized and phenolic compounds diminished, while the processes of starch degradation, lautering and extract yield are generally considered to be negatively affected [1]. However, the significance of the influence of oxygen at this stage of the process has been called into question [2, 3].
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Oxygen is required for yeast reproduction immediately prior to the beginning of fermentation. However, excess oxygen can foster the formation of elevated concentrations of undesirable fermentation by-products. Downstream from primary fermentation, oxidation exerts an undesirable influence on the substances in beer, where the most harmful effects occur following filtration.
In the packaged beer, aside from the dissolved oxygen taken up during filtration and filling processes, the oxygen remaining in the headspace of bottles and cans is of consequence, as it can enter the beer through gas exchange.
Through the use of a properly designed filter with a well-devised system of bright tanks, wherein the tanks are thoroughly purged with CO2 prior to filling, as well as suitable bottling and kegging lines, values for oxygen as low as 0.1 mg/l can be reached at the filter inlet and below 0.3 mg/l in the finished beer [4–7].
Literatur
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L. Narziß, BWelt 127, 207, 1987
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F. Schur, BR 97,117, 1986
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H. Hug, P. Anderegg, H. Mändli und H. Pfenninger BR 97, 113, 1986
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F. Ullmann BR 92, 143, 1981
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H. G. Bellmer, BWelt 122, 1150 und 1166, 1982
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L. Narziß, BWelt 122, 2293, 1982
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P. Hoeren, MB 30, 36, 1977
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Through heating and shaking, the gases contained in beer are collected in a burette filled with potassium hydroxide. The carbon dioxide is bound by potassium hydroxide, and the remaining volume of gas, consisting of oxygen and nitrogen, is measured [1].