Organoleptic defects

However, on a second glance one finds that the world of manifold heterocyclic compounds has entered into one of the most ancient cultural drinks of the world. Besides numerous O-heterocycles, several 0,N-, N,S-and N-heterocycles have been detected in wine that can impart organoleptic defects and off-flavors. 

Ribereau-Gayon, P., Glories, Y, Maujean, A., Dubourdieu, D. (2000a) Chemical nature, origins and consequences of the main organoleptic defects. In P. Ribereau-Gayon (Ed.), Handbook of Etiology, Vol 2, (pp. 209-253). Chichester John Wiley sons. Ltd. 

Since yeast lees may adsorb some aroma compounds responsible of off-flavours in wines (volatile phenols), these components have been also proposed such as a cost-effective and efficient approach to remove or to decrease organoleptic defects in wine (Chassagne et al. 2005). 

Bade-Wegner et al. (1998) studied the volatile compounds associated with the over-fermented flavor defect, considered to be one of the most objectionable organoleptic defects in coffee. They examined two defective samples of arabica and one sample of robusta green coffees, comparing them to reference products with a neutral flavor. As the off-flavor can be due to overfermentation of green coffee or to the presence of so-called stinker beans, the authors considered that the previous studies and identifications were more indicative than causative. By GC-olfactometry, three fruity odor notes were perceived, at different intensities, that were attributed to ethyl 2-methylbutanoate (Section 5,F.40), ethyl 3-methyl-butanoate (Section 5,F.41) and ethyl cyclohexanecarboxylate (Section 5,F.46). The three esters were considered to be the most important contributors to the over-fermented flavor defect. 

Chemical Nature, Origins and Consequences of the Main Organoleptic Defects... 

Organoleptic defects associated with grapes affected by various types of... 

This chapter deals exclusively with organoleptic defects that develop during aging. Some are of chemical origin (oxidation, reduction and contact with certain materials), but microbiological processes are often involved, even in the development of cork taint and spoilage due to sulfur derivatives. The various problems caused by anaerobic lactic bacteria are described, as well as the role of acetic bacteria. The mycodermic yeasts responsible for/tor are included in Section 8.3. 

An oxidative phase during aging is indispensable to ensure normal color development, particularly in red wines (Ribereau-Gayon et ai, 1983). Excessive oxidation in any type of wine, however, results in an organoleptic defect known as flatness (Section 8.2.3). 

Flatness involves several transformations (Ribe-rean-Gayon et al, 1976). Initially, a few mg/1 of oxygen combined with wine causes the disappearance or modification of certain odors. The wine also develops the freshly cut apple smell of ethanal. However, this combined oxygen is also responsible for the development of a bitter, acrid taste. The rate at which a wine becomes flat depends on temperature. The same reactions may take several days in winter but only a few hours in summer. When a flat wine is kept in an airtight container, this organoleptic defect disappears more rapidly at higher temperatures. 

Excessive amounts of acetic acid in wine are due to the action of anaerobic lactic bacteria or aerobic acetic bacteria. Together with other molecules, this acid plays a major part in organoleptic defects of bacterial origin. On the other hand, myco-dermic (Section 8.3.4) and Brettanomyces yeasts (Section 8.4.6) cause defects that do not involve accumulations of this acid. 

Over the past 15 years, much research has been done and over twenty articles of real scientific value have been published on this subject. These articles examine the composition of cork in terms of volatile compounds, especially those molecules likely to cause organoleptic defects in wine. 

Organoleptic defects in wine due to the presence of thiols, or mercaptans, are often associated with a reduced character. This link between reduction flavors and the presence of sulfur compounds is easily justifiable. Indeed, one characteristic of thiol-disulfide redox systems is its particularly low normal potential (E q) values (—270 < Eq < —220 mV), compared to the redox potential values of wines (-1-220 < E < - -450 mV). It is, therefore, quite clear that the presence of thiols in a wine, and the corresponding hydrogen sulfide smells, require an abnormally low oxidation-reduction potential. This is totally consistent with the impression of reduction on the palate. 

ORGANOLEPTIC DEFECTS ASSOCIATED WITH GRAPES AFFECTED BY VARIOUS TYPES OF ROT... 

At the end of the operation, the water is drained from the filter and, at the same time, it is filled with wine. However, after flushing with the quantity of water necessary for sterilization, a 40 cm x 40 cm filter sheet retains approximately 0.85 1 of liquid. It is, therefore, essential to eliminate the first wine that is filtered (at least one liter per sheet), as it is highly diluted and may have slight organoleptic defects. 

Philippe Darriet for his research into the organoleptic defects of wine made from grapes affected by rot (Chapter 8)... 

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