Veraison in Martinborough NZ

During the stage from berry set to veraison (when the berries are small, hard and green), sugar is mainly used for berry growth and chemical reactions within berry cells.  Veraison signals the onset of berry ripening (as seen in these Pinot Noir grapes from Murdoch James Estate in Martinborough NZ), and now sugar begins to accumulate in the berries.

The sugar is stored in special compartments within the berry cells, mainly in the flesh.  From veraison to harvest the sugar content of the berries increases dramatically, and berries become obviously sweet to taste.

The sugar concentration of the juice is usually expressed in units of Baume.  The measurement of the sugar concentration of the juice gives an indication of the approximate potential alcohol level of the wine made from those grapes and gives a broad guide to the style of the wine, eg:

• Sparkling wines are normally produced from grapes with sugar levels in the order of 9 - 11 degrees Baume
• Light-bodied dry white (Sauvignon Blanc) or red wines (Pinot Noir) are normally produced from grapes with sugar levels between 10-12 degrees Baume
  
• Full-bodied dry white (Riesling) or red wines (Shiraz) are normally produced from grapes with sugar levels in the order of 12-14 degrees Baume
  
• Sweet wines are normally produced from grapes with very high sugar levels >14 degrees Baume

Apart from the increase in sugar in the berries during veraison, many other changes also occur.  The berries soften, take up water, increase in size, decrease in acidity, change colour and develop distinctive aromas and flavours.