Wine Chemistry and Biochemistry

(Steven Felgate) #1

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.

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