Continued notes and comments from the Wines and Spirit Educational Trust course.Please note for original material refer to the WSET course book, the below are extracts.
The most important part of the process is fermentation. When yeast feeds on sugar in the grape juice they produce alcohol, carbon dioxide and heat, changing the flavours of the grape juice into wine. The flesh of almost all wine grape varieties is white. To colour of red wine and rose is obtained by soaking the skins in the fermentation process. If the skins are removed early on, little or no colour is left in the wine, this is how rose is made from black grapes for example.
Red wine is made from black grapes only and white wine can be made from black or white grapes.
For white wines the grapes are usually crushed to break the skins before they’re pressed to separate out the juice. Yeast is added at this stage. The must is transferred to the fermentation vessel, usually a stainless steel tank or oak barrel. White wines are fermented at low temperatures, generally 12-22 degrees Celsius, to preserve the delicate fruit aromas. This take between two-four weeks. Sweetness in white wines is caused by unfermented sugar.
Black grapes for red wines are crushed to release the juice, then the juice and the skins are put in the fermenting vessel together. Fermentation takes place at a higher temperature for red wines than white wines at 20-32 degrees Celsius. Alcohol helps the extraction of colour, flavour and the tannins from the skins. To keep the juice in contact with the skins, and thus obtain its colour, the juice can be pumped over the skins or the skins are punched down into the juice.
The amount of colour and tannins in the wine will depend on the amount of contact time the juice has with the skins as well as how much is in the skins, this varies depending on the grape variety. Hot climates also encourage higher colour and levels of tannins in the grapes. In some case the wine can be fermented for up to two weeks, like most quality Bordeaux for example, or up to 5 days for light wines such as Beaujolais.
When enough colour and tannins have been extracted the free run wine is drawn off and the skins are then pressed yielding a further quantity of wine, known as the ‘press wine’. The press wine contains higher levels of tannins and may be added to the free wine to produce the style required.
Like Red wine, Rose must be made from black grapes although with a shorter grapeskin contact time, 12-36 hours. The method is similar to that of Red wines but must be fermented at lower temperatures, typically 12- 22 degrees celsius.
Many wines receive some contact with oak, this can range from staves (small planks) or chips (large splinters) added to the vat of wine. In the finest wines, oak contact is achieved through ageing the wine in oak barrels. Oak, particularly new oak, is expensive so this will impact the final selling price. European oak is more expensive than American oak, but tends to give more subtle, toast and nutty flavours with smoother tannins. American oak gives sweeter coconut and vanilla but harsher tannins. The labour intensive maintenance of looking after wine in oak barrels is expensive due to having to make sure the barrel is always topped up to avoid air in the cask spoiling the wine. Fermentation and ageing in oak barrels is common for premium Chardonnay wines, including many made in Burgundy. It is impractical to ferment red wines in barrels, but many premium red wines are aged in oak.
Can take place in barrels or large neutral wooden or stainless steel vats. It also continues to take place in the bottle after bottling. It’s the slow changes in chemical reactions that can allow complex flavours to develop.
Maturation with Oxygen
The use of oak barrels and vats means the wine becomes penetrable by small amounts of oxygen which then dissolves into the wine. This softens the tannins in red wine and can make the wine taste smoother, adding flavours such as toffee, fig, hazelnut, almond, walnut and coffee to develop.
Maturation without Oxygen
Bottles, cement and stainless steel vats are airtight and do not add any flavours, thus the chemical reactions are different to that of maturation in oak. The wine generally stays unchanged for months. In bottles, the fresh fruit aromas of young wines change into cooked fruit, vegetable and animal notes (wet leaves, mushroom, leather).
Few wines improve in the bottle. It is common for the attractive fruit flavours to simply fade away. For a few special wines the fruit character remains, while other complex flavours develop around it. These wines are not easy to make and end up being very costly, however the flavours they offer are the most rewarding of all.