Grape berries follow a
double sigmoid growth curve. The initial phase of berry growth is a result of
cell division and
cell expansion. As berry growth of phase I slows this is termed the lag phase. The lag phase is not a physiological growth stage, but an artificial designation between the two growth periods of grape berry development. Post-veraison,
fruit acidity decreases due to degradation of
malic acid. The degradation of malic acid during ripening makes
tartaric acid the predominant acid; grape berries also possess a small amount of citric acid. Tartaric acid accumulates early in phase I of berry growth, while malic acid accumulates at the end of phase I berry growth. At the same time as acidity decreases,
hexose sugars are accumulated. The accumulation of hexose sugars (
glucose,
fructose) is associated with the development of
xylem cell discontinuities which reduce the volume of water entering the berry relative to the volume of sugar, resulting in an increase in sugar concentration. Physiologically, the sugar concentration can increase to around 25 percent via sugar development. Further increases in sugar concentration are due to dehydration of the fruit. The deposition of
sugar into the berry depends on the level of leaf
photosynthesis, the number of competing sinks on the vine and sugar accumulation. As ripening continues, the fruit becomes attractive to animals due to changes in aroma from acidic to sweet with fruitiness. As ripening occurs, herbaceous aromas (e.g.
methoxypyrazines) are degraded. It is unknown whether the degradation of herbaceous aromas allows fruit aromas to be detected, or if fruity aromas develop later in berry ripening. The berry also changes in color, presumably because
chlorophyll is broken down. In white cultivars,
carotenoids are formed, while in red cultivars,
anthocyanins and
xanthophylls are formed. The trigger of veraison is unknown, but may signify the seed reaching maturity, an unlikely signal, however, because seedless berries also proceed through veraison. ==Other uses==