Grape juice acid concentrations

The base wine is prepared from grape juice or concentrate as for normal dry table wines (Amerine et ah, 1980 Jackson, 2008). The essential requirements of the base wine are that the wine be sound, neutral-flavored, and inexpensive (Joshi et ah, 2011a,b). For example, wine prepared largely from Ugni Blanc in Emilia is popular for Italian vermouths. The wine is fairly neutral in flavor with 10-11% (v/v) alcohol and low acidity (05-0.6%). 

The complexity of wine composition is a central reason for the vast variety of wines in the marketplace. In addition to water and ethanol, the major components, a variety of organic acids as well as metal ions from minerals in the skin of the grape are present. Initially, all of these substances remain dissolved in the bottled grape juice. As the fermentation process occurs, the increasing alcohol concentration in the wine alters the solubility of particular combinations of acid and metal ions. Unable to remain in solution, the insoluble substances settle as crystals. Since the process of red-wine making involves extended contact of the grape juice with the skins of the grapes (where the minerals are concentrated), wine crystals are more common in red wines than in white wines. 

However, in view of quantities consumed by other populations, wines could make a significant contribution for tartaric acid conjugates and grapes and grape juice for caftaric acid, respectively. Lettuce is the major source of chicoric (dicaffeoyltartaric) and caffeoylmalic acid (up to 3 mg/100 g), but endive may have twice the concentration. Spinach is almost certainly the richest source of conjugated p-coumaric acid at some 30-35 mg/100 g [18]. 

Monk, P. R., Cowley, P. J. (1984) Effect of nicotinic acid and sugar concentration of grape juice and temperature on accumulation of acetic acid during yeast fermentation. Journal of Fermentation Technology, 62, 515-521. 

Polyphenolic compounds can interfere in the analysis of red wines, and amino acids in the analysis of grape juices. Consequently several methods for isolating biogenic amines from wines and juices have been proposed liquid-liquid extraction with butanol of the sample preliminarily concentrated and adjusted to pH 1.5 (Almy et al, 1983) in general, for SPE is preferred strong cation exchange (SCX) under... 

Amino acids are the most prevalent form of total nitrogen by weight in grape juice and wine. Indeed, the total free amino acid concentration varies from 1 to 4 g/1, depending on the year. In ripe grapes, amino acids generally represent 30-40% of total nitrogen. 

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