Acetic acid in wines

A major cause of wine spoilage by AAB is the production of excessive acetic acid. The legal limit for acetic acid in wine is 1.2-1.4 g/L, concentrations that also greatly reduce wine quality (Drysdale and Fleet, 1989a Sponholz, 1993). Drysdale and Fleet (1989a) reported that as much as 50-60% of the ethanol content of a wine could be oxidized by these bacteria with the production of 1.5-3.75 g/L of acetic acid. 

Lactobacillus is generally considered undesirable in wine because uncontrolled growth can lead to increases in VA or formation of other adverse odors or flavors. Some species produce excessive amounts of acetic acid (Davis et al., 1986b Edwards et al., 1999 Huang et al., 1996). As evidence, L. kunkeei can produce between 3 and 5 g/L of acetic acid in wines (Edwards et al., 1999 Huang et al., 1996). 

The oxidization of ethanol to acetic acid in wine is catalyzed by enzymes. 

Excessive amounts of acetic acid in wine are due to the action of anaerobic lactic bacteria or aerobic acetic bacteria. Together with other molecules, this acid plays a major part in organoleptic defects of bacterial origin. On the other hand, myco-dermic (Section 8.3.4) and Brettanomyces yeasts (Section 8.4.6) cause defects that do not involve accumulations of this acid. 

The quantity of acetic acid formed during alcoholic fermentation usually does not exceed 0.3 g/L in wine. The U.S. limits for volatile acids in wine are 1.2 and 1.1 g/L for red and white table wines, respectively. The aroma threshold for acetic acid in red wine varies from 0.6 to 0.9 g/L. Elimination of air and the use of sulfur dioxide will limit the increased amount of acetic acid in wine. Formic acid is usually found in diseased wines, propionic acid is usually found in traces in old wines. On the contrary, the production of acetic acid is desired in vinegar production. The acetic acid bacteria convert the alcohol into acetic acid by the process of oxidation. The... 

Although there are no legal limits on the concentration of ethyl acetate, the concentrations of acetic acid are regulated (Table 11.1). The maximum legal limits for acetic acid in wine in the United States are 0.9 to 1.7 g/L depending on the wine. Processing methods are available to reduce acetic acid from wines above the legal limit (Section 8.7.2). 

The control of preservatives in foods is important due to potential problems for example, a high concentration of acetic acid in wine results in spoilage of the product. Due to the potential undesirable effect of acetic acid and acetate salts, their content in foods and beverages should be limited. Hence, the monitoring of these preservatives is desirable. 

Vinegar (acetic acid in water) Wine (ethyl alcohol in water) ... 

Total Acid. Simple titration procedures are used to determine total acidity. Problems arise because of the widely varying amounts of different acids in wines tartaric, malic, citric, lactic, succinic, acetic, etc. Different pKtt values for these acids make it impossible to predetermine easily the correct pH of the endpoint. Since a strong base is being used to titrate relatively weak acids, the endpoint will be greater than pH 7. In this country phenolphthalein (8.3) or cresol red (7.7) endpoints or a pH meter to 9.0 have been used (3, 6, 12, 76, 77) and the results are expressed as tartaric acid. The result at pH 7.7 X 1.05 approximately equals the result of titrating to pH 8.4. In Europe pH 7 is usually the endpoint, in France the results are expressed as sulfuric acid, and in Germany as tartaric or in milliequivalents (78). 

These acids are found ready-made in nature in great numbers. Some of them occur as free acids (citric acid, tannic acid, malic acid), others as esters (products of acids and alcohols, such as fats and oils and the flavors of many fruits and the odors of many flowers). Still other of these organic acids are produced by the action of bacteria (acetic acid from wine or cider, lactic acid when milk turns sour, butyric acid in rancid hutter). 

Quantitative (total tartaric acid). 100 c.c. of the vinegar are treated in a beaker with 1 c.c. of 20% potassium acetate solution and 15 grams of powdered potassium chloride. When the latter has dissolved, 20 c.c. of 95% alcohol are added, the subsequent procedure being as indicated for the determination of the total tartaric acid in wine q.v., p. 193). 

While the wine contains several g/L of L-malic acid before MLR, it usually only contains between 200 mg/L and 300 mg/L of citric acid. Although the citric acid is only present in low concentrations, it is of considerable importance. On the one hand, its metabolic pathway leads to production of acetic acid, in other words, it increases the volatile acidity of the wine. However, the most important enological significance associated with fermentation of citrate is the production of diacetyl and other acetonic compounds, which affect the wine aroma. 

Yeast strain, and nutrient status of the must and fermentation conditions, many of which affect growth or induce physiological stress, modulate the accumulation of acetic and other fatty acids in wine. Reported factors include must sugar concentration, nutrient balance, inoculum level, fermentation temperature, pH and aeration (Delfini and Costa 1993 Henschke and Jiranek 1993 Shimazu and Watanabe 1981). The effects of osmotic stress, as induced by sugar concentration, on acetic acid production are discussed in Sect. 8D.3.2. 

The quantity of NADH oxidised in reaction (3) is determined by measuring its absorbance at 340 nm, which is proportional to the concentration of acetic acid in the wine. 

Acetic acid represents the only organic acid of normal olfactory sensory significance to wines (27). While acetic acid may be formed by . cerevisiae, the concentrations produced are typically less than 300 mg/L (55), far lower than the concentrations produced by spoilage microorganisms (he, Acetobacter) which are the predominate source (52). Apiculate yeasts may also serve as a source of acetic acid Romano et ah (36) found that Kl apiculata typically produced greater than 200 mg/L acetic acid in synthetic medium fermentations. 

The mother-liquors obtained from 4 4 -dihydroxydiphenyIarsinic acid by method (2) in the foregoing, after standing for about four hours, deposit heavy aggregates of stout, glistening prisms. These are filtered off after forty-eight hours and washed with water. The product separates from 50 per cent, acetic acid in prisms, M.pt. 215° to 217° C. with gas e% olution, and gives a wine-red colour with ferric chloride. 

Acetic Fermentation.—Acetic acid in addition to its occurrence in nature in the form of esters is produced on the large scale by the acid fermentation (oxidation) of the alcohol obtained as the result of fermenting fruit juices which contain sugar, especially apple juice or cider, and wine. When the sugar present in cider is fermented, dueTo the action of the enzyme zymase, alcohol is produced (p. 95). This alcohol is then oxidized through the activity of an aerobic bacterial organism Bacterium aceti, which is present naturally in the fruit juice. The product is acetic acid. 

Acetic acid is one of the main products of AAB metabolism and is found in many foods as the result of the presence and activity of these bacteria. Acetic acid is also a major volatile acid in wine but also one of the... 

Organic acid content in wine has an important impact on organoleptic characteristics of the wine. a-Hydroxy acids (tartaric, malic, lactic, and citric acids) are mainly responsible for these characteristics. Other acids in wines include acetic, ascorbic, gluconic, and sorbic acids, as well as sulfite, sulphate, phosphate, and malonate (Masar et al., 2001). 

To separate neutral phenolics from phenolic acids in wine [190] and apple juice [179-180], an extraction with ethyl acetate at fixed pH values of seven and two has been proposed. Extraction efficiencies determined with standard solutions of (+)-catechin, (-)-epicatechin and procyanidin... 

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