science

What is it in sherry cooking wine that makes it less effective in killing bacteria when it has a pH of 3.5, compared to a tomato, with a pH of 3.7. The bacteria is Serratia marcescens. I have been searching for the chemical compositions of both to compare and all I found was that both were antioxdiants, however the tomato conatins citric acid, and I don't think the sherry cooking wine does.

I googgled grape acidity
slightly more than 1/2 way down are your grape acids.

Acids are present naturally in grapes; they're also produced during the fermentation process. The acid content of grapes can be affected by several factors. Climate, for instance, plays a major role. Wines made from grapes grown in hot viticultural regions or during particularly hot seasons have lower levels of acid. Conversely, cooler regions or growing seasons produce wines with a higher acid concentration. Soil is another component affecting the acid concentration in grapes. For example, potassium-deficient soil may produce high-acid grapes. An additional determining factor is the grape variety itself-chenin blanc is intrinsically high in acid, whereas malbec is a relatively low-acid grape. In the proper proportion, acids are desirable-they give wine character much as a dash of vinegar or lemon juice heightens the flavor of many foods. On the other hand, too much acid leaves a sharp, tart taste in the mouth, while too little makes wine seem flat and lifeless. The three primary acids in grapes are tartaric, malic, and citric, all of which are inherent to the fruit. Tartaric acid, the principal organic acid in grapes, contributes crisp flavor and graceful aging to wine. Malic acid, the second principal acid in grapes, gives wine a fruity essence. Citric acid comprises only a fractional amount of a grape's acid. Wine also contains minute to trace amounts of other acids produced during fermentation including: acetic, butyric, capric, caproic, caprylic, carbonic (in sparkling wines), formic, lactic, lauric, propionic, and succinic. The least desirable of these is acetic acid, which-when present in more than a nominal amount-gives wine a sour or vinegary aspect (see acetic; volatile acidity). Volatile acids (such as acetic and butyric) are those that can be altered-for instance, they can evaporate. Fixed acids are fruit acids (such as malic and tartaric) that are organic to the grape. Total acidity, also called titratable acidity, is the sum of the fixed and volatile acids, which is determined by a chemical process called titration. In the United States the total acidity is usually expressed in terms of tartaric acid, even though the other acids are measured. Total acidity is expressed either as a percentage or as grams per liter. In warm growing regions where grape acidity is lower (like California), natural grape acids can legally be added to wine to increase acid levels. This acid adjustment process is called acidification (sometimes acidulation). Less practiced by winemakers is deacidification, the acid adjustment process of lowerering acid in wines through any number of methods including cold stabilization and amelioration. malolactic fermentation also lowers acidity and helps soften the edges of an acidic wine. See also acidic; acidity; ascorbic acid; ph; tartrates.

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asked by Kate

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