Tannins content changes

This shift from wood to stainless steel cooperage has been general and a factor in changing production practices around the world, particularly for red wines. A wine well protected from oxidation in an impervious tank will not change rapidly in tannin content. If it was vinified so as to be too tannic for acceptance by the consumer, it is likely to remain... 

In addition to the molecnlar strnctnre, the tan-nin/anthocyanin ratio also affects wine development. Color has been observed to change rapidly due to anthocyanin breakdown reactions when the medinm has a low tannin content (molar ratio T/A tannin polymerization reactions when the tannin concentration is much higher than the anthocyanin content (molar ratio T j A < 4). If a wine is to develop harmoniously, this ratio should be between 1 and 4, i.e. 500 mg of anthocyanins and 1-3 g of tannins per liter of wine. 

The strongly astringent taste of persimmon fruits arises from soluble tannins that accumulate in large specialized cells called tannin cells. In this chapter, some chemical properties of persimmon tannins, an outline of simple and reliable methods for estimation of the degree of astringency and the amount of tannins, and some aspects of the physiological changes in the tannin contents of persimmon fruits will be described. 

Swain T, Hillis WE (1959) The phenolic constituents of Prunus domestica. I. The quantitative analysis of phenolic constituents. J Sci Food Agric 10 63-68 Taira S, Shimomura M, Oba S, Watanabe S (1990) Changes in soluble and total tannin content during fruit development and their relation to removal of astringency in Japanese persimmon Diospyros kaki Thunb.). Abstr XXIII Int Horticultural Congr, 27 Aug-1 Sept 1990, Firenze, vol 2, no 3279... 

Chang, S.I., and Fuller, H.L., 1964, Effect of tannin content of grain sorghums on their feeding values for growing chicks. Poultry Sci., 43 30. 

Feeny P P, Bostock H 1968 Seasonal changes in the tannin content of oak leaves. Phytochemistry 7 871-880... 

Temperatures above 20°C are dangerous during barrel aging. Excessive heat may cause irreversible color breakdown and the formation of tannin polymers that do not always soften the wine. These changes are even more extreme in wines with a low phenol content and in oxidized media. It is always dangerous to barrel-age wines in cellars without temperature control. Furthermore, higher microbial risks are likely to lead to an increase in volatile acidity. 

A wine s behavior dnring aging therefore depends on a whole series of factors related to its composition. These inclnde not only phenol content, but also the type of tannins and their structures, as well as the tannin/anthocyanin ratio and the polysaccharide concentration. Fnrthermore, the wine s initial composition changes dnring aging, developing complex new strnctnres likely to slow down the process of stripping. 

Black Tea. The freshly harvested leaves are spread out on mats and allowed to dry slowly and wither, after which they are mechanically rolled and broken to liberate the oxidase enzymes present in the cell sap and ensure their close contact with precursors. The rolled leaves are then fermented for several hours, usually in baskets or spread out under damp cloths. During this stage the colorless tea tannins are partially oxidized, changing to a reddish brown color, and some essential oil is formed. This primary oxidation gives to the leaves a very agreeable odor and color and determines the flavor quality, strength, body, and color of tea made from them. The process is stopped by firing at about 85°C. This induces a secondary oxidation, a reduction in moisture content to about 5% and the full development of the characteristic tea odor and color. The whole process demands skill and experience to achieve a consistent quality. 

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