Olfactory defects

Cork flavor, or the olfactory defect caused by moulds, is the commonest of the undesirable flavors found in wine. In most cases, the cork is responsible for tainting wine with 2,4,6-trichloroanisol (TCA) (Tanner et al. 1981). However, barrelled wine may also be contaminated with 2,3,4,6-tetrachloroanisol (TeCA) that can be present in the damp atmosphere of wine cellars in the presence of woods treated by polychlorophenols. TCA has a slightly different aroma than TeCA but the two contaminants are often confused. Another possibility is that the cork itself may be contaminated by other corks (TCA) or by TeCA. 

Among the other volatile products likely to contribute to wine aroma are volatile phenols and sulfur derivatives. The latter are responsible for olfactory defects whose causes and consequences are now well-known and are described elsewhere... 

Sulfur compounds in the thiol family (or mercap-tans) are generally held responsible for olfactory defects (Section 8.2.2). However, their major contribution to the aromas of certain fruits and aromatic plants has been clearly estabhshed. Thus, specific thiols are involved in the characteristic aromas of fruits such as blackcurrant (Rigaud et al., 1986), grapefruit (Demole et al., 1982), passion fruit (Engel and Tressel, 1991) and guava (Idstein and Schreier, 1985 Bassols and Demole, 1994). Two mercaptans, ethyl-3-mercaptopropion-ate and ethyl-2-mercaptopropionate, have been identifled as components in the aroma of Vitis labrusca grapes (variety Concord) (Kolor, 1983 Winter et al, 1990). 

Before they are marked enough to be perceived and identified in fasting, these defects detract from the finesse of normal fruity aromas. They then lead to a certain loss of character often described as heaviness. At higher concentrations, the defects themselves are clearly identifiable. It would be wrong to consider that these olfactory defects add complexity to a wine. One of the main objectives in enology over the next few years will certainly be to find out how to avoid these problems and their consequences. 

Besides acetic acid, lactic spoilage produces lactic acid and various secondary compounds that contribute to various olfactory defects. Some bacteria convert fructose into mannitol, explaining why this phenomenon used to be known as man-nitic fermentation. 

The Volatile Phenols Responsible for Olfactory Defects in Wines Known Collectively as the Phenol Character... 

Fig. 8.3. Volatile phenols responsible for olfactory defects in wine known as phenol odors ...

Olfactory defects in wine attributable to volatile phenols are relatively common. In a recent study (Chatonnet et al., 1993b), one hundred (mainly French) wines, from different appellations and vintages, were classified according to their volatile phenol content. Almost one-third of the red... 

The sulfides and thiols involved in this type of olfactory defect are divided into two categories heavy (boiling point above 90°C) and... 

It has been shown by Chukwudebe (1984) and Rauhut et al. (1986) for -methyl-O-methyl-Al-acetyl phosphoramide and Dittrich (1987) for oxime carbamate that the hydrolysis of these two compounds (Figures 8.24 and 8.25) produces methanethiol. This is the principal substance responsible for olfactory defects. Methanethiol may be accompanied by its oxidation by-product, dimethyldisulfide, formed as a result of the oxidation-reduction balance ... 

This olfactory defect actually gives wine a smell reminiscent of mice. It occurs in wine stored under... 

Mousiness has long been believed to be caused by the presence of acetamide (CH3-CO-NH2). Heresztyn (1986a, 1986b) associated this olfactory defect with two function isomers (I and II) of... 

Besides charcoal, ancient enology treatises mention other products likely to eliminate unpleasant smells and off-flavors toasted barley or wheat, mustard flour, oil, milk, etc. All these have practically disappeared from use. Fresh yeast lees are permitted in treating wine and are effective in eliminating a number of olfactory defects. This has already been mentioned in connection with fixing certain thiols, such as methanethiol (Section 8.6.2). This treatment is also recommended for adsorbing chloroanisoles in moldy wines (Section 8.5.2). 

Pons M., Dauphin B., La Guerche S., Pons A., Lavigne-Cruege V., Shinkaruk S., Banner D., Richard T., Monti J.-P., Darriet P. Identification of impact odorants contributing to fresh mushroom off-flavor in wines incidence of their reactivity with nitrogen compounds on the decrease of the olfactory defect. Journal of Agricultural and Food Chemistry, 59 3264-3272 (2011). 

Moving head presses have the significant advantage of being automatic and sometimes programmable. Chains and press rotation are used to break up the cake after decompression. This operation produces suspended solids and can lead to olfactory defects. 

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