In April this year, late frost caused damage to vineyards in some of France’s most famous winemaking regions, including Champagne, Bordeaux and Burgundy. Innovative ways to combat the cold included candles, heaters and even the down-draught from helicopters. And while in this case, timing was the biggest problem – frost in Spring damages early shoots – a good cold and wet winter is generally beneficial to vineyards.
Although winter conditions in cooler climates can injure grapes because of too low temperatures, Southern Hemisphere winters need to cool down sufficiently to allow vines to enter their resting phase. In a warm climate like South Africa and after two consecutive short winters with low rainfall (40% down on the long term), a proper cold and wet 2017 winter is of the essence. Winter arrived late but announced itself properly with a much publicized winter storm in the middle of June. Temperatures are low, we have had some rain and even a light dusting of snow on the Franschhoek mountains.
But why is a proper winter so important to the winemaker?
As temperatures fall and days get shorter, interesting physiological changes take place in the vine enabling it to survive the cold. The leaves change from green to yellow to brown and then start falling off. (Interestingly enough, although the bright purple and red leaves are lovely to look at and make for exceptionally beautiful pictures, they are a sign of stress in the plant.)
Now the vine’s metabolism slows down. No energy is produced through photosynthesis and the plant survives on the stored energy of the growing season. Having enough stored energy is very important as it will be used in spring to restart the growth cycle.
No water is absorbed during winter and cell water is moved to an inter-cellular area to protect the plant from damage should this water freeze in winter. With carbohydrates stored in the lower parts of the vine and as there are no leaves in the way, winter is also the ideal time for pruning.
A cold and wet winter is therefore important for the quality of the harvest. Ideal conditions include sufficient cold units and enough water. In dryer climates such as ours, groundwater as well as reservoir volumes for irrigation also need to be replenished to survive the warm months ahead.