Grape acid content

Acid content calculated as tartaric acid is about 6—7 g/L for best flavor and stabiUty. It is higher for tart low Brix musts and less important for sweet high Brix musts. High acid levels coiacide with a higher level of the second acid of grapes, malic acid. 

Wine Making. Wine making is one of the principal areas of tartaric acid use. There is a relationship between the size of the grape crop and its tartaric acid content when grapes are pressed. In poor harvest years, the tartaric acid content is low in good harvest years, the tartaric acid content is high. Thus, in poor harvest years, tartaric acid often is added to correct acid deficiencies in wine. 

Crops, food, and feed. The first recommended method is based on the Dutch Multiresidue Method 2 for A-methylcarbamates, which was originally developed by de Kok et The method has recently been validated by DuPont Crop Protection and Batelle, Geneva Research Centres, for the analysis of methomyl and oxamyl in dry, high-water, high-fat, and high-acid content crops and in various grape processed products. The limit of detection for each analyte is 0.003-0.005 mg kg . ... 

Grapes are one of the few fruit crops that contain a significant amount of the weak organic acid known as tartaric acid, HOOC-(CHOH)2-COOH. More than half of the acid content of wine is ascribed to tartaric acid. As a weak acid, tartaric acid partially ionizes in water to yield the bitartrate or hydrogen tartrate ion ... 

Ascorbic acid level in grapes is relatively low compared with other fruits. Zubeckis (5) in Canada reported that ascorbic acid in fresh grapes varied from 1.1 to 11.7 mg/100 ml juice, except for the variety Veeport. This Canadian variety contained a high content of ascorbic acid (33.8 mg/100 ml juice). More recently, Oumac (188) determined the ascorbic acid content of seven grape juices and found a range from 2.0 to 6.0 mg/100 ml. 

The range of pH and total acid values found in commercial musts of five native and two hybrid varieties for a six-year period (18) are given in Table III. Total acidity and pH were determined in filtered must samples representative of each day s total production, first noting pH then titrating to pH 8.2 using a Beckman Zeromatic pH meter (27). Only the Niagara grape consistently had a total acid content below 1.000... 

Figure I. Changes in Brix and acid contents of Concord grapes during...

Acetic acid content is used as a criterion for aerobic bacterial spoilage in wines. We can easily analyze two wines and determine that one has a lower volatile acidity than the other. But by every available standard of product quality judgment, the wine with the higher level of acetic acid may be the superior product. It is no accident that Subpart ZZ, Part 240, Title 26 of the Code of Federal Regulations allows the direct addition of acetic acid to correct natural deficiencies in grape wine. As sanitation practices have improved, the so-called natural acetic acid content diminished, and this has been correlated with lower consumer acceptance in certain cases (2). 

Low pantothenic acid content (0.1-0 5 milligram/100 grams) Almond, apple, banana, bean (kidney), cabbage, grape, grapefruit, honey, lemon, lettuce, lobster, milk, molasses, onion, orange, oyster, peach, pear, pepper (white and sweet), pineapple, plum, potato, shrimp, tomato, turnip, veal, watercress. 

B. cinerea utilizes a significant part of the grape s assimilable nitrogen content, including ammonium and amino acids. In some studies, a significant decrease (by 30-80%) in the total amino acid content has been reported in Botrytis-affected grapes, compared to the healthy grapes (Dittrich and Sponholz, 1975 Dittrich et ah, 1975 Rapp and Reuther, 1971). 

Bitartrate Stabilization. Potassium and tartaric acid are natural constituents of the grape. Wine content of these constituents depends on a number of variables, not all well understood variety, vintage, and weather pattern degree of skin contact alcohol level bitartrate holding capacity of phenolic compounds and potassium binding capacity of the wine (30, 35). Most wines after fermentation are supersaturated solutions of potassium bitartrate. This compound is less soluble at lower temperatures, and, thus, lower temperatures will cause precipitation of bitartrate crystals. This lowering of temperature and subsequent removal of crystals by filtration is called cold stabilization. 

Delfini, C., Contemo, L., Giacosa, D., Cocito, C., Ravaglia, S., Bardi, L. (1992) Influence of clarification and suspended solid contact on the oxygen demand and long-chain fatty acid contents of free run, macerated and pressed grape musts, in relation to acetic acid production. Viticultural andEnological Sciences, 47, 69-75. 

Kim, D.-H., Hong, Y.-A., Park, H.-D. (2008) Co-fermentation of grape must by Issatchenkia orientalis and Saccharomyces cerevisiae reduces the malic acid content in wine. Biotechnology Letters, DOl 10.1007/sl0529-008-9726-l. 

When the grapes are crushed a portion of juice is tested for its sugar and acid content. A proper sugar content should be between 20 and 28% and a deficiency requires only a simple calculation and the addition of the calculated amount of ordinary cane sugar. 

Ascorbic acid (vitamin C) is utilized as a cofactor to stabilize the chloroplast stroma, in quenching free radicals and reacting with hydroxy radicals and in the biosynthesis of tartaric acid and oxalic acid (6), important organic acids in grapes, and many vegetables. The effect of CA on ascorbic acid content differs with commodity,... 

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