Grafting has been an important element of viticulture since the end of the 19th century when the phylloxera louse decimated Europe’s vineyards. After numerous diverse attempts to get the pest under control, it was discovered that grafting onto resistant rootstocks was the solution to the catastrophe.
Grafting involves the connection of two pieces, in this case, of vine material so that they join and grow together as one plant. The scion from one variety is grafted onto the rootstock of another. Traditionally it was done by hand in the field (field grafting) or indoors (bench grafting), although nowadays much is done by machine.
Vines are usually grafted to a rootstock which offers beneficial properties that the scion does not possession; for example, resistance to phylloxera or nematodes, tolerance to soil characteristics such as salinity, lime, excess water or drought.
Grafting may also be carried out to change the variety and thus eliminate the need to replant an entire vineyard. This is known as top grafting.
In viticulture, a large difference between daytime and night-time temperatures is generally believed to be beneficial. Warm days encourage the build-up of sugars, whilst cool nights aid the retention of fruit aromas and acidity. This difference is known as diurnal range.
In certain cooler climate wine regions, the grapes may not ripen sufficiently to produce a must high enough in sugar. In such cases, you are permitted to chaptalise, i.e. add beet or cane sugar to enrich the unfermented grape must. This will lead to an increase in alcohol content after fermentation. This practice is also known as must enrichment.
It is strictly forbidden in many countries and regions. However, it is generally allowed in some regions where the grapes tend to have low sugar content, for example some regions in Germany and northern France.
Although we usually think of the fruit that grows on vines as grapes, and this is what they are usually called, in wine-making terms, this individual grape is often referred to as a berry.
This berry is formed of the berry skin (epidermis), the berry pulp, or flesh, (the part of the berry containing the juice) and seeds.
The layer just under the skin is called the peripheral pulp. This is where most of the coloured pigments, tannins and flavour constituents can be found.
In order to make red wine, the juice of the black grapes is fermented with the skins in order to extract flavour, tannins and colour.
If you want to make a white wine, or indeed a sparkling wine such as Champagne, from black grapes, then the juice has to be separated from the skins before fermentation. The juice itself is clear.
The seeds contain a high level of tannins and can make a wine bitter if too much of these are released during pressing.