Grape seed maturity

Table X. Phenolic Compounds in Grape Seeds at Crop Maturity in Vineyard SC...

Romeyer, F, Macheix, J. J., Sapis, J. C. (1986). Changes and importance of oligomeric procyanidins during maturation of grape seeds. Phytochemistry, 25, 219-221. 

Tannin, which is derived by extraction from the skins, seeds and stems of the grape is an essential constituent of the wine. It serves to confer disease resistance on the wine, aids remarkably in the clarification and produces a more brilliant color. On the other hand, an excess of tannin confers an astringence on the wine which delays its final maturity, although in the end the wine is more mellow for it. 

Grape pomace polyphenol composition is affected by many different factors. It is variety dependant [10-11] and, within the same variety, different parts have significantly different compositions. For example, the grape skins, have been found to be rich in anthocyanins, hydroxycinnamic acids, flavanols and flavonol glycosides, whereas the seed portion is a good source of gallic acid and flavanols [3, 11]. Polyphenol composition is also influenced by the growing location, climate, maturity and fermentation time [12]. 

Table 10.1. Relationship between nnmber of seeds and berry size at maturity Mo-lot variety grapes sampled in 1982 in a Saint-Emilion vineyard (France)...

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. 

More recently, researchers have focused on the evolution of phenolic compounds during maturation, but the technique of separating the skins from the seeds is awkward and exacting limiting its practical applicability. There is now a rapid whole-berry grinding technique. The grape grinding is followed by a differential phenolic... 

White wines are produced from both black and, more traditionally, white varieties of grapes. The berries are crushed gently rather than pressed to prevent breaking of stems and seeds. Solid material is removed and the clarified juice fermented typically between 16 and 20°C for 5 days. The resultant must then undergoes malo-lactic fermentation, before maturation, filtration and bottling. 

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