How does the grape get from the vineyard to the bottle on the shelf? How does soil affect wine quality? What exactly does oak do?
Winemaking – the climate
Most of the world’s vineyards are planted in the temperate latitude zones of 30-50 degrees North and 30-50 degrees South. Within these zones the actual climate has a huge influence on the type of wine produced.
In a cool country like Germany, the grapes will ripen slowly. Even if they are not picked until the end of October, they will retain high levels of acidity. Much of this acid goes right through the winemaking and ends up in the finished wine. Not good if you have an ulcer, but crucial to the balance of most great white wines.
Conversely, the build-up of sugar will be very slow. Without much sugar in the grapes, the resulting wine will be relatively light in alcohol. Of course a hot climate will have the opposite effect, usually giving wines with a hefty blast of alcohol and soft acidity.
Like most plants, vines need a decent amount of water to survive and flourish. Historically it made sense to plant vineyards in places where the climate delivers a reliable annual rainfall. Think of the Atlantic dominated climate of Western Europe. With irrigation it is possible to plant vines in some pretty arid places, such as the Central Valley in Chile, the Riverland in Australia, and Washington state – where about the only naturally-occurring vegetation is sagebrush.
With the rise in the temperature the buds will burst and growth starts. This spurt of spring growth produces a profusion of shoots and leaves. Warmth and some rain will help to keep this vigorous growing phase on track.
The grower has to be vigilant for the first sign of any pests and diseases, and apply the appropriate sprays or biological controls. At the end of the spring period the vines flower.
Assuming the flowering was successful, a crop of grapes will set. Dry, warm and sunny weather is then required to swell and ripen those grapes. The vines may need to be trimmed to keep the vineyard neat and to allow good sun exposure and air circulation. This technique is also used to keep the yield down. If the crop looks like being excessive some properties will cut away some of the immature bunches. Spraying against pests and diseases continues. In the early part of the summer all the grapes are green in colour. Towards the end of summer the colour forms in the skin of the black grapes, a process called ‘veraison’.
A final period of fine weather is needed to complete the ripening of the grapes and to harvest them. Some grape picking is still done by hand. Whilst this is obviously labour intensive and very costly, it does allow the grapes to be sorted carefully at the vineyard or winery. Machine picking is much quicker and cheaper, but it does not allow the same rigorous grape sorting. That said, machine picking can be particularly advantageous in hot climates as it allows harvesting in the cool of night. However they’re picked, the grapes need to be transported from the vineyard to the winery as quickly as possible. A few weeks after picking the vines will lose their leaves, and they then shut down for the winter dormancy.
During the winter months the vine is dormant. A period of frost and snow is actually beneficial, helping to kill off over-wintering pests and diseases. Heavy rain is also welcomed as it allows the soil to replenish its water reserves. A lot of general maintenance takes place in the vineyard, with trellises repaired and fertilisers applied. The main winter chore for the grower is to prune the vines. There are a number of vine pruning and training systems in use today. The Guyot system which is used extensively in France involves pruning the vine back to just on or two canes, and then training these along wires. The more old-fashioned bush training system has no wires, the vines being pruned back to an unsupported gnarled trunk. This ancient technique can still be seen in several Mediterranean countries, as well as in a number of the oldest vineyards in Australia and California.