With the Maltese 2012 harvest in full swing, our red grapes are entering their final stage of ripening, often referred to as veraison.
Veraison is where the young, immature red grapes, which at this time of year are a very dark green colour, with a somewhat hard texture, start to take on their natural colour. This happens when the chlorophyll in the berry skin is replaced by anthocyanins (or carotenoids in white grape varieties).
The berries also start to soften and begin to accumulate glucose and fructose. The natural sugars and the volume then start to increase and the acidity levels starts to fall, usually within six days from the start of veraison.
The onset of this process does not occur for all berries at the same time, even within the same bunch.
Typically, the berries and clusters that are exposed to the most warmth – those on the outer extents of the leaf canopy – undergo veraison first. The berries and clusters closer to the trunk and under the canopy shade will undergo the process last.
The colour change from green to red, the depth and exact hue of the red will depend on the variety.
Grape varieties like Cabernet Sauvignon, Syrah and Merlot will be almost black, whereas grapes such as Pinot Noir, Grenache and Sangiovese will be lighter and redder in comparison.
In white grapes, the colour will go from a dark green to a kind of a yellowish green colour (again depending on the variety) and the skins will become more transparent.