A key yeast metabolite and oxidation product. Tyler Thomas, 2004
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Table I. Acetaldehyde levels in alcoholic beveragesa |
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Type |
Acetaldehyde (mg/L) |
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Red Wine |
4 – 212 |
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White Wine |
11 – 493 |
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Sweet wine |
188 – 248 |
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Sherry |
90 – 500 |
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Brandy |
63 – 308 |
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Cognac |
105 |
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aData summarized from Liu et. al. (2000). |
Acetaldehyde (CH3CHO) is a volatile compound found in wine. Levels in various wines are listed in Table I. On average, red wines contain 30 mg/L, white 80 mg/L, and Sherries 300 mg/L. The high levels in sherry are considered a unique feature of this wine. At low levels acetaldehyde can contribute pleasant fruity aromas to a wine, however, at higher levels the aroma is considered a defect and is reminiscent of rotten-apples. The threshold in wine ranges between 100-125 mg/L.
Acetaldehyde is one of the most important sensory carbonyl compounds in wine and constitutes approximately 90% of the total aldehyde content in wine. Acetaldehyde can be formed by yeasts and acetic acid bacteria (AAB). AAB form acetaldehyde by oxidizing ethanol. The amount formed by yeasts varies with species, but is considered to be a leakage product of the alcoholic fermentation. Additionally, film yeasts (important in sherry production) will oxidize ethanol to form acetaldehyde. Oxygen, and SO2 can all impact the amount of acetaldehyde formed by yeasts. Wines fermented in the presence of SO2 have considerably higher amounts of acetaldehyde. This is related to SO2 resistance of certain yeasts. In wine, acetaldehyde concentration increases with higher temperatures, though production was higher at cooler temperatures in fermented cider with Saccharomyces cereviseae. Acetaldehyde can also be formed as a result of oxidation of phenolic compounds. Hydrogen peroxide, a product of phenolic oxidation, will oxidize ethanol to acetaldehyde.
At wine pH (3-4), SO2 consists mainly of bisulfite (HSO3-), and small amounts of molecular (SO2) and sulfite ion (SO32-). The bisulfite can form complexes with carbonyl compounds, predominately acetaldehyde. The binding of acetaldehyde to bisulfite limits its sensory contribution to wine. Addition of SO2 to ‘inhibit’ acetaldehyde production may reduce the perceived aldehyde aroma character, but is most likely only masking the aroma contribution of the acetaldehyde that is present instead of actually inhibiting its production.
Summarized from:
Liu S.Q. and G.J. Pilone. 2000. An overview of formation and roles of acetaldehyde in winemaking with emphasis on microbiological implications. International J. of Food Science and Technology 35:49-61
Tyler Thomas, 2004