9D Influence of Phenolics on Wine Organoleptic Properties 551
Gawel et al. (2000) have proposed an interesting hierarchically structured vocabu-
lary of mouth-feel sensations, presentedas a “Mouth-feel Wheel”, to assist tasters
in their interpretation of wine astringency. Nevertheless, this new vocabulary seems
to be too extensive, which hampers their implementation in a common language.
In contrast to other foods, astringency in red wine is one of the major attributes
that the most exigent consumers of red wines learn to like. The levels of astrin-
gency in high quality red wines should be balanced: low levels of astringency could
lead to the wine being flat and uninteresting, and an excess could mask other wine
characteristics and make it harsh and dry (Gawel 1998).
Astringency is often the last sensation felt since it is a dynamic process that
requires a period of time to develop. Lesschaeve and Noble (2005) evaluated the
time-intensity curves of the astringency perceived from a red wine and observed
that its intensity reaches a maximum 6–8 s after wine ingestion. Moreover, they also
observed that the astringency intensity is build-up when the samples are tasted: the
maximal intensity of astringency increased with repeating sipping of red wine at
25-s intervals (Lesschaeve and Noble 2005). Nevertheless, the perception capacity
of astringency and bitterness change between individuals depending on intrinsic fac-
tors, such as the salivary protein composition and the flow-rate of saliva. Although
the physicochemical mechanism of astringency is not completely understood, it
is widely accepted that astringency results from the interaction between tannins
and salivary proteins, resulting in the formation of protein-tannin aggregates in the
mouth (Haslam 1998a; de Wijk and Prinz 2005). Some experimental evidence for
this hypothesis was provided by Kallithraka et al. (1998) who observed a loss in
saliva proteins after the tasting of astringent tannin-rich solutions and red wines,
as a result of their complexation with phenolic compounds. Other authors have
established a linear correlation between the astringency of tannin-rich solutions,
perceived by a taste panel, and the capacity of those solutions to precipitate proteins
(Llaudy et al. 2004; Monteleone et al. 2004; Troszynska et al. 2006).
There are many other factors that influence astringency in wine such as pH,
sweetness, viscosity and levels of ethanol. The role of ethanol, the second most
important component in wines, in wine taste is not totally clear. Fischer & Noble
(1994) observed only a slight decrease of astringency of a white wine when its
alcohol level rose from 8 vol.% to 14 vol.% while bitterness increases consider-
ably. According to Gawel (1998) and our own point-of-view, the presence of other
substances (carbohydrates, glycerol, etc.) in complex beverages such as wine and
beer could be responsible for the perception of subtle sub-descriptors of astrin-
gency, such as soft, grainy, harsh, green, chalky, that are not perceived in tannin
model solutions.
9D.3.2 Interactions Between Proteins and Tannins
The term “tannin” is often carelessly employed to identify some phenolic com-
pounds as a result of the structural ambiguity of that wide group of compounds.