Grape tannin content

The glycosidic anthocyanins are almost completely precipitated with red wines of a few months age and normal tannin content. However, with young wines made from the same grapes, a ros6 wine with only 713 mg GAE/liter total phenol gave 311 mg GAE/liter as not-precipitated nonflavonoid, and with increasing levels of total phenol in red wines to... 

One danger is that because herbal medications are not regulated, few if any clinical trials are performed even for safety or efficacy. One example is bilberry. Bilberry fruit is used to treat diabetes and diabetic retinopathy. Although animal models support the antioxidant role in vasoprotection, no well-designed and conducted clinical trials exist.The antioxidant effect may have benefit in AMD, as well. The antioxidant efficacy in bilberry is likely due to the tannin content, which is also found in grapes. 

This diversity explains the existence of tannins with different properties, especially as regards flavor, in various types of grapes and wine. Tannin content should not be the only factor considered, as structure and colloidal status also affect the impression tannins give on tasting. 

If the grape seeds have a low tannin content (MP < 15). There is no risk of excess tannin from the seeds affecting the quality of the wine. On the contrary, every effort should be made to achieve maximum extraction, as these tannins are indispensable for good balance and structure. Pumping-over and high temperatures... 

In dry white wines, the total phenol content is between 50 and 250 mg/1, or less than 10% of the value in red wines. It is even lower in sweet wines, made from grapes affected by noble rot. Indeed, the development of Botrytis cinerea is accompanied by a large-scale breakdown of the phenolic compounds in the skins. Only tyrosol remains, as well as the components from seeds (gaUic acid, catechin and procyanidins). Although their deep yellow color might seem to indicate the contrary, these wines always have a very low tannin content. 

Table 72.1 Anthocyanin and tannin content in the different parts of the grape berry ...

In conclusion, only the best grape varieties grown on the best terroirs produce wines that combine the high tannin content indicative of aging potential with aromatic finesse and complexity. On tasting, these wines are not only superbly concentrated, but also well-balanced and elegant. Winemakers today are aware that excessive tannin extraction tends to mask a wine s fruit and that perfect balance is the sign of a well-made wine. 

Proanthocyanidins (PAs), also known as condensed tannins, are oligomeric and polymeric flavan-3-ols. Procyanidins are the main PAs in foods however, prodelphinidins and propelargonidins have also been identified (Gu and others 2004). The main food sources of total PAs are cinnamon, 8084 mg/100 g FW, and sorghum, 3937 mg/100 g FW. Other important sources of PAs are beans, red wine, nuts, and chocolate, their content ranging between 180 and 300 mg/100 g FW. In fruits, berries and plums are the major sources, with 213.6 and 199.9 mg/100 g FW, respectively. Apples and grapes are intermediate sources of PAs (60 to 90 mg/100 g FW), and the content of PAs in other fruits is less than 40 mg/100 g FW. In the majority of vegetables PAs are not detected, but they can be found in small concentrations in Indian squash (14.8 mg/ 100 g FW) (Gu and others, 2004 US Department of Agriculture, 2004). 

Tannins are present in the skins of red grapes and play an important part in the flavor profile of red wine. Tannins in grapes are usually estimated in terms of the content of gallic acid (Amerine and Joslyn 1970). 

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