Formation and Removal of Acetoin During Yeast Fermentation

Abstract

The main yeast fermentation process can be characterized by two separate phases, the acetoin-producing phase (phase I) and the acetoin-reducing phase (phase II). The time at which yeast changes from production to removal is here designated as the 'point of metabolic change'. The rise and fall in acetoin concen tration was affected by composition of the wort, inoculum size, yeast strain, presence of traces of oxygen and addition of ergosterol, whereas temperature seemed to be of somewhat less importance. A high and positive correlation between the maximum level of acetoin and the concentration of ethanol measured at the 'point of metabolic change' has been demonstrated. The appearance of the 'point of metabolic change' is discussed in light of the level of acetoin in finished beer. The absolute threshold for acetoin was determined as 17 ppm.

Generation of Acetoin and Its Derivatives in Foods

“…For example, the sensation threshold of acetoin in different types of beers is quite different, ranging from 6 to 50 ppm by different authors. 1 In contrast, its reported levels of use in foods could be hundreds of parts per million (Table 1).…”

“…As the threshold for taste is affected by various conditions such as temperature, solution, and personal physiological and psychological status, acetoin is perceptible at different levels in different foods and drinks. For example, the sensation threshold of acetoin in different types of beers is quite different, ranging from 6 to 50 ppm by different authors . In contrast, its reported levels of use in foods could be hundreds of parts per million (Table ).…”

Capacitive Field‐Effect Biosensor Applied for the Detection of Acetoin in Alcoholic Beverages and Fermentation Broths

“…[12] Measuring the acetoin concentration during the production process of wine and beer can serve for quality management as it has a negative effect on the beer flavor if it exceeds a certain concentration level, and in addition, unnecessary maturation time can be avoided. [13,14] Typical acetoin concentrations in red wine and beer are in the range of 100-200 and 10-50 Â 10 À6 M, respectively. [13,15,16] Apart from its significance in alcoholic beverages, acetoin detection plays also an important role in biotechnological applications, where it can be used as an indicator for the metabolic activity of bacteria during fermentation processes.…”

“…[13,14] Typical acetoin concentrations in red wine and beer are in the range of 100-200 and 10-50 Â 10 À6 M, respectively. [13,15,16] Apart from its significance in alcoholic beverages, acetoin detection plays also an important role in biotechnological applications, where it can be used as an indicator for the metabolic activity of bacteria during fermentation processes. [17] In addition, the production of acetoin itself is of great interest because it is widely used in food production, as chemical raw material, and as a precursor in the synthesis of liquid fuels by microorganisms.…”

Synthesis of (R)- and (S)-acetoin (3-hydroxybutan-2-one)

“…The m.p.s of the 1-phenylethylammonium salt, the rotations of the corresponding hydrogen phthalate, and the m.p.s and optical rotations of the corresponding dicyclohexylammonium salt are given in Table 2. (6) The (-)-1-phenylethylammonium salt of the hydrogen phthalate (RS)-2-Methyl6utane-2,3-diol.-A solution of (RS)-acetoin (8.8 g, 0.1 mol) in ether (50 ml) was added slowly with stirring to a solution of methylmagnesium iodide ( 2 ~; 100 ml) at 0 "C. The mixture was boiled under reflux for 1.5 h and cooled. Hydrochloric acid ( 2 ~; 100 ml) was added slowly.…”