8F Interactions Between Wine Matrix Macro-Components and Aroma Compounds 431
compound volatility. They found asalting outeffect for acetaldehyde, ethyl acetate,
methanol and ethanol at salt concentrations from 0.5 to 2 mol/L, while other volatile
compounds, such as propanol, and 1-butanol, were not affected. Interestingly, they
did not find increased headspace concentrations of these volatiles as they increased
the CaCl 2 levels above 2 mol/L. One has to question if salting out was actually the
mechanism responsible for increased headspace concentrations of volatiles since
0.5 mol/L is relatively low for that mechanism to be effective and one would expect
increased salting out with increased CaCl 2 concentrations (up to saturation).
It has been suggested that the addition of potassium bitartrate/tartaric acid to
wines could induce a competition of thesecompounds for the free water involved
in solvation enhancing ethanol aggregation. Although Escalona et al. (2001) did not
find any effect of the addition of these compounds to model wine systems flavoured
with ethyl hexanoate, they found a decrease in the activity coefficient of octanal.
They explained this by the possible reactivity of the carbonyl group of the aldehyde
with hydroxyl radicals.
In some winemaking practices, wine is aged in wood for a relatively long period
of time. This practice is important to winearoma because during this period the wine
acquires anaged bouquet,gaining aroma compounds transferred from the wood.
The major wood components are able todonate or accept electrons, giving wood an
acid-base character (Escalona et al. 2001). Moreover, lignin has hydrophobic sites;
thus wood can absorb aroma compounds from wine. Ram ́ırez-Ram ́ırez et al. (2001)
and Chasagne et al. (2003) have reported the sorption capacity of oak wood for
some aroma compounds, notably ethyl esters, under conditions simulating oak aging
of wine. The composition of the wine itself can influence this absorption, e.g. the
concentration of ethanol may changethe solubility of some aroma compounds in
the wine. Ram ́ırez-Ram ́ırez et al. (2004) observed good agreement between the
hydrophobicity of a model aroma compound and the percentage of it absorbed by
the wood. They also observed a reduction in the amount of volatiles absorbed by
the wood as the alcohol concentration increased, e.g. for some esters the amount
absorbed by wood in 10% ethanol media was half of the amount absorbed at 0%.
They found the lowest absorption for most of the volatile compounds studied at
15% ethanol – the highest level studied. This fact could be due for the increasing in
solubility for most of thearoma compounds. As expected, the type of aroma com-
pound is also important in determining absorption by wood. For example, Hartmann
et al. (2002) did not find any effect on the volatility of alkyl-methoxypyrazines (no
interaction) when white oak sawdust was introduced to model wine systems.
8F.3 Conclusions and Future Trends
The effects of the main wine macro-components on wine aroma has been discussed
in this chapter. Although these interactions have not received as much scientific
attention as other aspects of wine flavour, it is clear that it is necessary to consider
them since they may strongly influence the release of wine aroma components,
thereby influencing flavour perception by the consumer.