476 N. Terrier et al.
extraction from skins was not influenced by the alcohol content, although the final
concentration reached in water was lower than in 6.5% or 13% ethanol whereas
extraction of flavonoids from seeds increased with concentration of ethanol (Canals
et al. 2005). Whether this is due to their chemical structure, seed procyanidins being
less hydrophilic than other flavonoids, or to thedifferent characteristics of both plant
tissues is unknown.
Consequently, pre-fermentation maceration at low temperature increases the
level of anthocyanins and flavanols from pulp and skins while post-fermentation
maceration increases that of proanthocyanidins, as a result of enhanced extraction
from seeds (Cheynier et al. 2006).
Treatments favouring contact between solid and liquid phases such as pumping
over or punching down are traditionally used toenhance extraction. Alternative pro-
cesses have been proposed more recently. These include physical processes such as
thermovinification and flash release (inwhich the grapes are heated quickly at high
temperature (> 95 ◦C) and then placed under vacuum, to produce instant vaporiza-
tion and cooling) and the use of pectinolytic enzymes.
Flash release and thermovinification greatly accelerated extraction of all flavon-
oids from Grenache, Carignan or Mourvedre grapes and can be used to produce
polyphenol-enriched juices (Morel-Salmi et al. 2006). Maceration after flash release
treatment further increased extraction of flavonoids and especially of flavanols.
After maceration, the concentration of flavanols in flash release treated wines was
much higher than in the control wine while that of flavonols and anthocyanins was
hardly modified. The use of pectinolytic enzymes results in increased juice yield
(Berg 1959; Ough and Crowell 1979) along with increased browning of white wines
(Berg 1959) and faster colour development (Ough et al. 1975), enhanced extraction
of phenolic compounds and colour in red wines (Fernandez-Zurbano et al. 1999).
Numerous protocols have been proposedto estimate flavonoid extractibility from
grape and relate it to ripeness and crop quality. Such approaches have shown
that anthocyanin extraction increasesas they accumulate in the berries (Canals
et al. 2005; Fournand et al. 2006) but that their extraction yield is stable (Four-
nand et al. 2006). The rate of proanthocyanidin extraction from skins as well as the
quantity extracted remain constant throughout berry development. Extracted proan-
thocyanidins showed lower mDP and lower rate of galloylation than those remaining
in the marc. Although the extraction yield did not change, this selectivity was some-
what lower in riper grapes. Extraction of flavonols from shaded grapes appeared
more efficient than from sun exposed grapes, as the concentration of flavonols in
the simulated maceration was only decreased2.5-fold (vs 8-fold in the grape skins)
(Cortell and Kennedy 2006). The extraction rate of skin proanthocyanidins was
higher from sun exposed than from shaded grapes but the concentrations in both
extracts were similar (Cortell and Kennedy 2006).
Nevertheless, the proposed protocols do not simulate flavonoid extraction during
the maceration and fermentation process, as they do not reproduce the effect of
gradual alcohol accumulation, temperature increase and duration of the maceration
phase.