The Influence of 2-Acetohydroxy Acids on the Determination of Vicinal Diketones in Beer and During Fermentation

Abstract

During sampling and determination of diacetyl, 2-acetohydroxy acids are easily converted to vicinal diketones. A simple procedure for gas chromatographic deter* mination of diacetyl, 2-acetolactate, acetoin and the homologous compounds is given.By careful sampling, less than 0-01 ppm of diacetyt was detected during the main fermentation in one brewery, whereas another strain of brewer's yeast yielded a maximum of 1-7 ppm of diacetyl. When samples of fermenting liquids are exposed to air at 60°C, complete conversion of 2-acetohydroxy acids takes placein less than one hour. The possibility that part of 2-acetolactate may be converted to acetoin, how ever, cannot be excluded. In finished beer 2-acetolactate levels of 0-2-0-5 ppm were observed. During the main fermentation the values ranged from 0-5-2-5 ppm. IntroductionResults have recently appeared, however,

Application of the acetolactate decarboxylase from Lactobacillus casei for accelerated maturation of beer

“…Presumably, the striking difference in the stabilizing effect of zinc added during fermentation and during maturation reflects concomitant activation of the zinc transport system and the metabolic activity of the yeast cell. It was assumed, therefore, that it would be possible to effect conversion of acetolactate after the main fermentation by adding only small quantities of the acetolactate decarboxylase to the green beer, in particular if addition of the enzyme was carried out under careful exclusion of oxygen and thus without unduly activating the metabolic activity of the small quantities of yeast present in the maturing beer (9). From Table Ill it is apparent that it is indeed possible to effect the desired conversion of acetolactate in green beer in the course of 48 h at 5 ~ by addition of only 6 kU of acetolactate decarboxylase per litre of beer under careful exclusion of air and without enriching the beer with zinc in spite of the fact that the enzyme was found to be entirely quenched in the course of the 48 hours even under these conditions.…”

“…Vicinal diketones and their precursors were measured by gas-liquid chromatography as described by HAUKELI and LIE (9).…”

Diacetyl control during brewery fermentation via adaptive laboratory engineering of the lager yeast Saccharomyces pastorianus

“…The samples were then analysed by headspace gas chromatography (HP 6890 Series GC System, Hewlett-Packard, USA; HP-5 50 m × 320 µm × 1.05 µm column, Agilent, USA) with 2,3-hexanedione as an internal standard. The ‘total diacetyl’ results are a good indication of α-acetolactate levels due to the fact that free diacetyl is rapidly reduced by yeast, and therefore, only detectable at low concentrations in wort [20]. …”

“…Once released, α-acetolactate begins to be converted into diacetyl via a spontaneous non-enzymatic decarboxylation reaction. As this reaction occurs relatively slowly, the levels of pre-cursor are typically orders of magnitude higher than those of diacetyl [20]. Also, diacetyl, once formed, is rapidly taken up by yeast and reduced to less flavor-active compounds such as acetoin.…”

Improved Performances and Control of Beer Fermentation Using Encapsulated α-Acetolactate Decarboxylase and Modeling

“…Galzy and co‐workers in 1983 (27) estimated the Michaelis constant of diacetyl reductase (from Saccharomyces uvarum ) equal to K m2 = 30 mmol/L. The order of magnitude of diacetyl during beer fermentation is 10−20 μmol/L (28), so here too K m2 ≫ [DA] and …”