Volatile acidity in wine

Determination of Volatile Acidity in Wine and Must (Grape Juice)... 

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... 

Volatile acidity in wine is considered to be a highly important physicochemical parameter, to be monitored by analysis throughout the winemaking process. Although it is an integral part of total acidity, volatile acidity is clearly considered separately, even if it only represents a small fraction in quantitative terms. 

Volatile acidity in wine consists of free and combined forms of volatile acids. This explains why the official assay method for volatile acidity, by steam distillation, requires combined fractions to be rendered free and volatile by acidifying the wine with tartaric acid (approximately 0.5 g per 20 ml). Tartaric acid is stronger than the volatile acids, so it displaces them from their salts. 

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... 

Distilled and undistilled beverages contain acetic acid in abundance. Frequently it amounts to 40-95 % of the total volatile acids. Although the greatest part of the volatile acidity in wine consists of acetic acid, the remaining acids are nonetheless important aroma compounds. Many short-chain and long-chain acids, and in particular the branched-chain acids, have an appreciably strong odor. 

Cruess, W. V. 1935b. Further data on the effect of SO2 in preventing high volatile acidity in wines. Fruit Products J. 16, 324-327, 345. 

Joslyn, M. A. 1939. Report on volatile acids in wines. J. Assoc. Offic. Agr. Chemists... 

Picozzi, A. 1947. Method for determining volatile acidity in wines. Proc. llth Conf. Pure and Appl. Chem., London 194 S, 207-209. 

Additionally, early inoculation may result in production of acetic acid due to the presence of fermentable carbohydrates (Lafon-Lafourcade and Ribereau-Gayon, 1984 Ribereau-Gayon, 1985). However, Semon et al. (2001) did not observe excessive volatile acidities in wines inoculated early or during alcoholic fermentation with O. oeni, in agreement with other studies (Giannakopoulos et al., 1984 Beelman and Kunkee, 1985 Rodriguez et al., 1990 Edwards et al., 1991). Semon et al. (2001) noted that volatile acidities of Chardonnay wines inoculated with different strains of O. oeni prior to alcoholic fermentation were higher than those inoculated after completion of the fermentation, but not to undesirable concentrations (Table 8.4). 

Legal limits for volatile acidity in wines worldwide expressed as... 

Acetic acid is one of the most important aliphatic carboxylic acids, being the principal acid constituent of vinegars (5% w/v) and volatile acidity in wines. The food industry uses vinegar to preserve and season food at the same time. Determination of acidity by SIA is invariably based on titration with a base solution while the titration reaction is monitored by UV/Vis spectroscopy or potentiometry. 

An example of separation obtained with this method is reported in Fig. 2. Falque and Fernandez (23) study the influence of time of contact with the skins on the composition of the volatile fraction and of the carboxylic acids in wine produced from Treixadura grapes. Also, these authors quantify glycerol and ethanol, besides carboxylic acids and sugars, through the use of an Aminex HPX-87H (300 X 7.8 mm) column, but with the mobile phase of H2S04 0.65 mM at 75°C and a flow of 0.7 ml/min. They use a UV detector at 214 nm and an RI in series. The sample requires only a filtration at 0.45 /im, as described in their survey (24). 

To apply this rule, the alcoholic strength (by volume) and the fixed acidity of the wine are determined. The latter, expressed as sulphuric acid, is increased by 07 (this corresponding with the maximum value of the volatile acidity in ordinary normal wines), and the value thus obtained divided by the alcoholic strength the quotient is the ratio sought. 

Volatile acidity. In ordinary red wines this acidity is, on the average, 0-4— 0 8 gram per litre, expressed as acetic add, and in white wines is somewhat less. In some wines, rich in alcohol and extract, such as " vins de conpage," it may surpass the above limits without producing an acetous character. In any case, however, if the volatile acidity exceeds 2 grams per litre, the wine is unsuitable for consumption. 

Torrija, M.J., Beltran, G., Novo, M.T., Poblet, M., Guillamon, J.M., Mas, A., Rozes, N. (2003) Effect of fermentation temperature and Saccharomyces species on the cell fatty acid composition and presence of volatile compounds in wine. Int. J. Food Microbiol., 85, 127-136. 

EgUnton, J. M., Henschke, P. A. (1999) The occurrence of volatile acidity in Australian wines. Australian Grapegrower Winemaker, 426a, 7-12. 

More potent yeasts responsible for spoilages of wines with volatile phenols are of Brettanomyces/Dekkerra type that can produce the vinyl phenols and ethyl phenols of hydroxyl cinnamic acids. Ribdreau-Gayon et al. (2000) give an overview on this topic. Another source of volatile phenols is the oak wood of barrel and oak chips. These phenols are characterized by smoked and toasted aromas. Important volatile phenols in wine are depicted in Fig. 9C.4. 

Esters, not fusel alcohols, actually comprise the most abundant group of volatile compounds in wines Rapp (26) has listed over 300 esters and lactones found in grapes, musts and wines. The esters are largely responsible for the fmity aromas associated with wine (52), especially young wine (27). Of the esters, ethyl acetate predominates by some two orders of magnitude (see 40) however, the low aroma thresholds of a number of the fatty acid ethyl esters makes them of sensory import nonetheless (27). 

The fact that enologists need to distinguish between total acidity, pH and volatile acidity demonstrates the importance of the concept of acidity in wine. This is due to the different organoleptic effects of these three types of acidity. Indeed, in any professional tasting, the total acidity, pH and volatile acidity of the wine samples are always specified, together with the alcohol and residual sugar contents. 

Alcoholic fermentation of grapes normally leads to the formation of 0.2-0.3 g/1 of H2SO4 of volatile acidity in the corresponding wine. The presence of oxygen always promotes the formation of acetic acid. Thus, this acid is formed both... 

This series is shown in Table 2.4. The most important of these compounds is acetic acid, the essential component of volatile acidity. Its concentration, limited by legislation, indicates the extent of bacterial (lactic or acetic) activity and the resulting spoilage of the wine. As yeast forms a little acetic acid, there is some volatile acidity in all wines. Other C3 (propionic acid) and C4 acids (butyric acids) are also associated with bacterial spoilage. 

Table 2.4. Fatty acids in the aliphatic series among the volatile components in wine (Ribdrean-Gayon et al., 1982)...

Citric acid solnbilizes iron, forming soluble iron citrate. Citric acid is an anthorized additive at doses np to 0.5 g/1. The total concentration must never exceed 1 g/1. This treatment may only be envisaged for wines that have been sufficiently sulfured to protect them from bacterial activity that would otherwise break down the citric acid, producing volatile acidity. In practice, this treatment is used exclusively for white wines that are not very susceptible to ferric casse (with no more than 15 mg/1 of iron) and that will not be damaged by this acidification. Doses of 20-30 g/hl are usually sufficient. 

Benzene compounds. Benzene compounds are an important group in varietal aroma, abimdant in wines, including aromatic alcohols, aldehydes, volatile phenols and shikimic acid derivates. The volatile phenols in wines can come from grapes, both as free and bound aroma, or be generated during the alcoholic fermentation by chemical reactions such as phenolic add degradation, or in the case of vinylphenols due to brettanomyces contamination (Suarez et al., 2007). Volatile phenols are considered characteristic components of wine aroma, although their influence on the final product may be positive or... 

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