Wines esters

White juice fermentations are controlled at temperatures ranging from 7° C to 15° C. Most enologists feel that cooler, longer, slower fermentations give wines of greater fruitiness. Killian and Ough (29) have shown that fermentation temperatures affect both formation and retention of wine esters. 

Recent work has also indicated that commercially available strains of LAB are also able to synthesize acetates and ethyl fatty acid esters during winemaking (Maicas et al. 1999 Ugliano and Moio 2005), which appear to be in contradiction with early suggestions that the MLF could result in a decrease in wine esters (Davis et al. 1988 Du Plessis et al.2002). More research is required in this area before general conclusions can be drawn regarding the influence of MLF on the ester composition of wine. 

Essential oils are obtained from fmits and flowers (61,62). Volatile esters of short- and medium-chain carboxyHc acids or aromatic carboxyHc acids with short- and medium-chain alcohols are primary constituents of essential oils, eg, ethyl acetate in wines, brandy, and in fmits such as pineapple ben2yl acetate in jasmine and gardenia methyl saHcylate in oils of wintergreen and sweet birch. Most of these naturally occurring esters in essential oils have pleasant odors, and either they or their synthetic counterparts are used in the confectionery, beverage, perfume, cosmetic, and soap industries (see Oils, essential). 

This helps explain why a wine should be left to stand some of the natural alcohols in the wine are oxidized by oxygen dissolved from the air to form carboxylic acids. These acids then react with the natural alcohols to generate a wide range of esters, which connoisseurs of wines will recognize as a superior taste and bouquet . 

And the reason why the wine must stand (rather than the reaction occurring immediately the oxygen enters the bottle on opening) is that the reaction to form the ester is not a straightforward one-step reaction the first step (Equation (8.39)) is quite slow and occurs in low yield ... 

Premium wines, 26 300 Premixed flames laminar, 7 443—445 turbulent, 7 445-446 Premixes, silica in, 22 375 Premixing process, for fumed silica, 22 581 Prenal, 24 482 esters of, 24 483... 

Natural compounds are also applied as chiral ligands in enantioselective homogeneous metallo-catalysts. A classical example is the Sharpless epoxidation of primary allylic alcohols with tert-butyl hydroperoxide [37]. Here the diethyl ester of natural (R,R)-(+)-tartaric acid (a by-product of wine manufacture) is used as bi-dentate ligand of the Ti(iv) center. The enantiomeric excess is >90%. The addition of zeolite KA or NaA is essential [38], bringing about adsorption of traces of water and - by cation exchange - some ionization of the hydroperoxide. 

It has been suggested that the disulfides may subsequently be reduced back to the volatile thiols (with lower perception thresholds) by SO2 present in the wine during bottle storage under low oxygen concentrations (Bobet et ah, 1990), or be released by hydrolysis from thioacetate esters (Rauhut et ah, 1996). 

In an initial survey at the University of Auckland in 2004 on Cabernet Sauvignon, Merlot and Malbec wines, subject to MOX in 2000-L tanks at 4-8 mg/L/month for 12 weeks post-MLF, no changes were seen in the aroma profiles of the wines (vs. controls) for a wide range of aroma compounds, including herbaceous methoxypyrazines and C6 alcohols, floral terpenes and (3-ionone, or for fruity esters and higher alcohols (Rowdon, 2005). Likewise, the concentrations of the varietal thiol 3MH,... 

In the case of the esters, considered responsible for the fruity aromas of yoimg wines, there was no consistent difference brought about by the oxygenation procedure between the MOX (dotted lines) and control (solid... 

Ftg. 12. Plot on the discriminant functions of LDA. 3 categories of wine (Pinotage wines from Stellenbosch, Worcester, Durbanville). 16 variables (esters, alcohols, acids). (Adapted from Ref... 

Applying vacuum distillation in an one-stage process removes nearly 75% of the wine volatiles, predominantly owing to the transfer of esters and fusel alco-... 

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