Signs of change

Veraison. The official definition is the point at which the grapes change color. This is a beautiful time in the canopy of the grape vines! There is more to it than that of course, especially since not all grapes actually change color. This is a sign to the growers and winemakers that harvest preparation needs to start immediately if it is not almost done.

Grapes grow in what is termed a 'double sigmoid growth curve'. This means they initially grow in size (cell replication and expansion, the curve rises) then growth pauses for a bit, this pause is called the lag phase. Then at veraison the grapes start to ripen (the curve rises again) or accumulate sugars. During this time the acidity decreases because Malic acid is degraded, leaving tartaric acid as the main acid in the grapes. The top of this second curve indicates full ripeness, once completely ripe the plant no longer puts any effort into the berries and they start to die.

Although the plant is no longer producing more sugars for the berries does not always mean the grapes will be picked at that point. Once the plant stops caring about reproduction (fruit production) the berries of the grape clusters start to lose water retention due to the thinning of the outer waxy cuticle on the berry skin. This causes a higher sugar to water ratio, as well as an oxidation of some of the flavor/aroma compounds that can be highly coveted. The practice of leaving the grapes on the plant after they are ripe to get these effects is call 'hang time'