WINETECH Technical Yearbook 2021

TABLE 1. Some compounds that can cause the smoke spoilage of wine.

magnitude of this occurrence is not signif- icant, it confirms that winemakers need to be informed about the potential libera- tion of spoilage compounds. Viticulturists should also be aware of the evaluation of smoke-exposed vineyards to identify potential post-harvest vineyard practices. The magnitude of smoke exposure will influence the decision making regarding potential reactive actions. Analyses of the spoilage compounds are however expensive (USD 150 to 250 per sample), complex and not always available. Wine spoiled by smoke is not only a quality problem, but can also cause considerable financial losses. The potential solution to the problem is consequently of cardinal importance. Specific vineyard practices are the first step that can be implemented. It entails amongst other things the following: • Grapes can be treated with kaolin. • Foreign material other than grapes (MOG) must be limited. • Grapes must rather be handpicked. • Grapes must be cooled to 10°C if possible. After grapes have been delivered at the cellar, different actions can also be im- plemented. This includes specific fermen - tation protocols, separation of the press

Sensory threshold value in red wines (µg/L)

Sensory threshold value in water (µg/L)

Sensory threshold value in 10% alcohol (µg/L)

Compounds

Descriptor

Guaiacol

Smoky, medicinal

23

9.5

–

m-Cresol

Tar, medicinal, phenolic

20

15.0

–

p-Cresol

Tar, medicinal, phenolic

64

3.9

–

o-Cresol

Tar, medicinal, phenolic

62

–

31.0

4-Methylguaiacol

Vanillin, cloves, smoky

65

21.0

–

Syringol

Smoky, charcoal

–

–

570.0

4-Methylsyringol

Smoky, charcoal

–

10.0

and if present during veraison, the uptake of the vine is significant. In order to limit the toxicity of the com- pounds, the vine sequesters the compounds by forming glycosylated compounds. Veld fires occurring in the early season can deposit ash, which remain dormant until veraison, but will be absorbed by the vine. If glycosylase enzymes are afterwards used during winemaking, the glycosylated com- pounds can be hydrolysed and the spoilage compounds can be observed. Although the

found that a Pinot noir rosé blend, containing more than 6.25% tainted wine blend, can still be detected by consumers. Me thods to remove the nega t i ve compounds were investigated before and after harvesting, and before and after alcoholic fermentation. Smoke spoilage compounds can result at different stages and from di f ferent sources during winemaking. Guaiacols can for example also be formed by some spoilage yeasts. If free guaiacols are removed before bottling,

a wine can still exhibit spoilage thereafter if bound guaiacols are hydrolysed up to five years after bottling. The formation of smoke taint compounds on or in grapes have different causes. Its transfer into the resulting juice is also possible. The physiological and phenological stages of the vine, when it is exposed to smoke, determine the extent of spoilage. The potential of the uptake of taint compounds increases significantly during veraison. The spoilage compounds can be toxic to the vine

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