Grape pulp maturity

Most of the acids of the metabolism are found in trace amounts in ripe grape pulp (pyruvic, a-ketoglutaric, fumaric, galacturonic, shikimic, etc.). Must acidity, an important element of enological data, is essentially constituted by three acids tartaric, malic and citric acid (Volume 2, Section 1.2.2). It can vary from 3 to 10 g/1 in sulfuric acid or from 4.5 to 15 g/1 in tartaric acid, depending on the cultivar, the climate and grape maturity. Phosphoric acid is the preponderant inorganic anion. 

Fernandez, E. Cortes, S.M. Castro, M Gil, M. Gil, M.L. (1999). Distribution of free and glycosidically bound monoterpenes and norisoprenoids in the skin and pulp ofAlbarino grapes during 1998 maturation. In Oenologie 99 - 6 h Symposium International dOenologie, A. Lonvaud Funel (ed.), Bordeaux. TEC DOC Paris, pp. 161-164... 

The following phenolic compounds are present in the grape skin at maturity benzoic and cinnamic acid, flavonols and tannins. They are distribnted in the cells of the epidermis and the first snb-epidermal layers in both white and red grapes. In addition, the red grape skin contains anthocyanins, essentially located in the hypodermal cell layers. Exceptionally, in certain years, the cells adjacent to the pulp can be colored. The pulp itself is colored in the case of Tenturier varieties and some American vines or direct producer hybrids. Antho-cyanin composition varies from cultivar to cultivar, depending on the anthocyanidin substitution and heterosidic nature of the cultivar (see Volume 2, Section 6.2.3). 

The distribution of minerals in the grape berry is not insignificant and it has an impact on the composition of must at maturity. Potassium is essentially located in the pulp cell vacuoles, but the skin cells also sometimes contain significant amounts. 

The juice from mature grapes contains barely 20% of the total berry nitrogen. The remainder is retained in the skins and seeds, even though the latter are likely to liberate soluble forms of niffogen (ammonium cations and amino acids) in the pulp towards the end of maturation. 

---