Tannins in wine

Calculation of the theoretical levels of anthocyanins and tannins in wines is possible, assuming complete extraction of these compounds from the parts of the cluster. Thus one sees only 20-30% of the possible grape pigments in wine. 

Analysis of polymeric pigments in parallel with tannin in wines or grape extracts required two 1.5 mL microfiige tubes for each sample. The first tube was made up by adding 1 mL of the acetic acid/NaCl buffer to the tube and then adding 500 pL of the diluted skin extract or wine. One mL of the mixture was transferred to a cuvette and the absorbance at 520 nm was determined (reading... 

The values are between 5 and 40. At values above 35-40, the tannins in wine precipitate, thus decreasing the value. At the beginning of barrel aging, very light wine has a low value, between 5 and 10. A wine suitable for aging has a value of 10-25 and a wine with a high concentration of highly polymerized phenolic compounds has a value >25. 

Table 6.10. Effect of terroir (soil and microclimate) on the reactivity to proteins of tannins in wine gelatin index and tannic strength (TS) (Merlot from Saint-Emilion, 1992 vintage) (de Freitas, 1995)...

The Folin-Denis reagent was used by Rosenblatt and Peluso (1941) for the colorimetric determination of tannin in wines. Careful attention to details of temperature, time, and concentration is necessary, but the procedure is reported accurate to within... 

Ponte, A. and Gualdi, G. 1931. Tannin in wines and its estimation. J. Intern. Soc. Leather Trades Chem. 16, 151 for original see Boll, uffidale ataz. aper. ind. pelli mat. concianti 1981, 391-407. 

Pro, M. J. 1952. Report on apectrophotometric determination of tannin in wines and whiskies. J. 4ssoc. Offic. Agr. Chemists 36, 255-257. 

According to Joslyn and Goldstein (1964), the Folin-Denis method, published in 1912, was first intended for the measurement of tannins in wine and whiskey, and then used for the assay of tannins in fruits (Swain and Hillis 1959 Craft 1961). Various methods for phenolic compound analysis have been reported (Joslyn and Goldstein 1964 Hartley 1987 Karchesy 1989 Hagerman 1989), but the Folin-Denis method is still very useful for the measurement of phenolic compounds in fruits. 

Fig. 1. An amplified outline scheme of the making of various wiaes, alternative products, by-products, and associated wastes (23). Ovals = raw materials, sources rectangles = wines hexagon = alternative products (decreasing wine yield) diamond = wastes. To avoid some complexities, eg, all the wine vinegar and all carbonic maceration are indicated as red. This is usual, but not necessarily tme. Similarly, malolactic fermentation is desired in some white wines. FW = finished wine and always involves clarification and stabilization, as in 8, 11, 12, 13, 14, 15, 33, 34, followed by 39, 41, 42. It may or may not include maturation (38) or botde age (40), as indicated for usual styles. Stillage and lees may be treated to recover potassium bitartrate as a by-product. Pomace may also yield red pigment, seed oil, seed tannin, and wine spidts as by-products. Sweet wines are the result of either arresting fermentation at an incomplete stage (by fortification, refrigeration, or other means of yeast inactivation) or addition of juice or concentrate.

CZE is particularly useful for separating anthocyanin dimers or polymeric anthocyanins. Calvo et al. (2004)" separated 13 anthocyanins by CZE including acylated and non-acylated anthocyanins, pyranoanthocyanins, and flavonol derivatives in wine. Saenz-Lopez et al. (2004)" applied CZE to analyze wine aging (1 to 14 yr) as related to monomeric anthocyanins, anthocyanin derivatives, tannins, and fla-vonols. Bicard et al. (1999)" reported the improved detection sensitivity of anthocyanin chemical degradation analysis by CZE. 

Thiolysis also proved useful for the analysis of derived tannins. Methylmethine-linked tannin-like compounds resulting from acetaldehyde-mediated condensation of flavanols (see Section 5.5.S.2) yielded several adducts when submitted to acid-catalyzed cleavage in the presence of ethanethiol, providing information on the position of linkages in the original ethyl-linked compounds. " Thiolysis of red wine extracts released benzylthioether derivatives of several anthocyanin-flavanol adducts, indicating that such structures were initially linked to proanthocyanidins. However, some of the flavonoid derivatives present in wine (e.g., flavanol-anthocyanins ) are resistant to thiolysis, while others (e.g., flavanol-ethyl anthocyanins) were only partly cleaved. Thiolysis, thus, appears as a rather simple, sensitive, and powerful tool for quantification and characterization of proanthocyanidins, but provides mostly qualitative data for their reaction products. 

Downey, M., Harvey, J., and Robinson, S., Analysis of tannins in seeds and skins of Shiraz grapes throughout berry development. Aust. J. Grape Wine Res. 9, 15, 2003. 

Cheynier, V. et al., The structures of tannins in grapes and wines and their interactions with proteins. In Wine. Nutritional and Therapeutic Benefits (ed. T.R. Watkins), American Chemical Society, Washington, DC, 1997, p. 81. 

Riou, V. et ak. Aggregation of grape seed tannins in model — effect of wine polysaccharides. Food Hydrocoil 16, 17, 2002. 

Vidal, S. et al., Taste and mouth-feel properties of different types of tannin-like polyphenolic compounds and anthocyanins in wine. Anal Chim. Acta 513, 57, 2004. 

New enological technologies aim to lower volatile acidity, enhance sugar content in must in cool climates and vice versa reduce the alcohol content of wines from hot climates, modify pH, cations, anions and acidity to achieve tartrate stability, complement traditional ageing in oak barrels with the use of small oak wood particles and most recently, extract phenolic compounds by a countercurrent chromatography process from wine to diminish or enrich tannins in red wines. 

Phenylalanine and tyrosine also give rise to many commercially significant natural products, including the tannins that inhibit oxidation in wines alkaloids such as morphine, which have potent physiological effects and the flavoring of cinnamon oil (Fig. 22-28b), nutmeg, cloves, vanilla, cayenne pepper, and other products. 

Tannins, another group of phenolic substances, are known for their sensory effects on wine. In addition to their influence on the body of wines, tannins produce an astringent taste. Amerine and Joslyn (2) reported that the usual range of tannin content for white wines is from 0.01 to 0.04% and from 0.10 to 0.20% for red table wines. The threshold for tannin was reported as 0.10 gram/100 ml for a white table wine and 0.15 in a red table wine (137). Other studies have reported that tannin affects the detection levels for sweetness and tartness in wines (18, 138, 139). In addition to their influence on taste, tannins are responsible, in... 

Iron and copper in wines may form complexes with other components to produce deposits or clouds in white wines. Iron clouds generally occur at a pH range from 2.9 to 3.6 and are often controlled by adding citric acid to the wines (2). Copper clouds appear in wines when high levels of copper and sulfur dioxide exist and are a combination of sediments, protein-tannin, copper-protein, and copper-sulfur complexes (169). Further, the browning rate of white wines increases in the presence of copper and iron (143). The results of this study indicate that iron increased the browning rate more than copper. 

Bisulfite ions, HS03", condense with anthocyanins. This reversible reaction decreases the color by forming a colorless compound (12) (16). This effect is less evident in strongly acid media because the bisulfite ions are not as numerous since they are being converted to the undissociated acid. This property explains the decolorization of red wines following sulfite treatment but, since it is reversible, the color gradually reappears as the free S02 (bisulfite ions) disappears. The major role of tannins in the color of old wines explains their insensitivity to color change with SOo. 

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