Grape aroma formation

I. 210 but sometimes exceeds 1.235. The juice yield is very low (250-300 I/tonne) and only vertical hydraulic presses are capable of extraction. The resulting juice is extremely viscous and dark, with pronounced grape aromas. The Pedro Ximenez variety is particularly rich in organic acids. The heat of the Andalusian sun provokes the formation of a significant quantity (50-75 mg/1) of hydroxymethylfurfural from fructose. 

The next step of the biotechnical sequence, yeast fermentation, is of the utmost importance to the chemistry of winemaking as well as to the formation of flavor substances. We have investigated this previously using 14C-tagged compounds (16). Amino acids, for example, enter the yeast fermentation with a quasi biochemical valence with regard to the formation of metabolic side products like alcohols and esters. In that respect, the composition of the fermentation substrate, the grape must, is highly important to the formation of aroma substances by yeasts. 

Loscos, N., Hemandez-Orte, R, Cacho, J., Ferreira, V. (2007) Release and Formation of Varietal Aroma Compounds during Alcoholic Fermentation from Nonfloral Grape Odorless Flavor Precursors Fractions. J. Agric. Food Chem., 55, 6674-6684. 

Carotenoids are regarded as part of the aroma potential of grape, as they are the biogenetic precursors of C13-norisoprenoids, a chemical family with many powerful odorants, which are mainly found as glycoconjugates in grape (Baumes et al. 2002 Enzell 1985 Mathieu et al. 2005 Winterhalter 1993). Sunshine favors the biosynthesis of carotenoids in the berry, from the first stage of fruit formation... 

Certain enzymes present in grapes are responsible for wine problems such as clouding, darkening or an oxidized taste. To prevent this, wineries routinely treat must and wines with sulfur dioxide. In addition to its antimicrobial activity, SO2 has an antioxidative property which prevents browning and taste defects. Polyphenoloxidase has detrimental effects on wine quality. However enzymes are also responsable for the formation of certain desir able esters which are essential to the aroma or bouquet of the wine. 

Vernin G, Parkdnyi C (1982) Mechanisms of formation of heterocyclic compounds in Maillard and pyrolysis reactions. In Vernin G (ed) Chemistry of heterocyclic compounds in flavours and aromas. Ellis Horwood, Chichester, pp 151-207 Versini G, Dalla Serra A, DelPEva M, Scienza A, Rapp A (1988) Evidence of some glycosidically bound new monoterpenes and norisoprenoids in grapes. In Schreier P (eds) Bioflavor 87. de Gruyter, Berlin, pp 161-170... 

Finally, gray rot seriously affects Ihe aromatic distinctness of dry white wines. Varietal aromas are masked while dusty, dirty and moldy aromas appear. It also promotes the development of rancid, camphorated and waxy odors, appearing later during maturation and especially in the bottle. This type of olfactory flaw is comparable to a premature oxidative aging of white wines (Volume 2, Section 8.2.3). Gray rot is not solely responsible and white wines made from healthy grapes can also contain the flaw. The responsible compounds and their formation mechanisms remain to be discovered. 

Loscos N, Hemandez-Orte P, Cacho J, Ferreira V (2007) Release and formation of varietal aroma compounds during alcoholic fermentation from nonfloral grape odorless flavor precursors fractions. J Agric Food Chem 55(16) 6674—6684. doi 10.1021/jfl)702343 Martin VI, Pitera DJ, Withers ST, Newman JD, Keasling JD (2003) Engineering a mevalonate pathway in Escherichia coli for production of terpenoids. Nat Biotechnol 21(7) 796-802. doi 10.1038/nbt833... 

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