The use of oak during winemaking greatly determines the style of a wine. It impacts on the colour, structure, texture and flavour of resulting wine: the ageing of red wine in oak stabilizes the colour; tannins from the oak add to the structure of red and white wines develops structural complexity; and oak-derived flavours integrate into the wines giving secondary characteristics such as vanilla, butterscotch and smoke. As oak is porous in nature, some level of oxygen contact occurs and interacts with the wine which also softens wine texture. Little evaporation also occurs – wine becomes more concentrated in flavour profile and improves in quality along with quantity decline.
The most commonly used oak vessels in wineries are French and American oaks. There are three major differences between the two types of oak: species, price and flavour differences.
European barrels are made with more porous and finer grained oak species. The very best European oak unquestionably come from France and is more expensive than American oak. It is more costly and labour-intensive to make European barrels which reflect higher prices. French oaks are more subtle in contributing to toast and vanilla notes.
American oaks are less porous and thicker grained than European barrels. They tend to give sweeter and more intense flavours of vanilla and coconut to the wine and result in creamier wines.
Slavonian oak is another alternative which is extremely popular in Italy, particularly in Piemonte. Along with the characteristics of tight grain, medium tannins and low aromatics, these large barrels impart very subtle aromas and flavours into the wine (so the wine tastes more primary of fruit notes rather than oak-associated flavours) with softer tannins.
Many wines have oak flavours added into them rather than spending time in actual oak barrels. This is achieved by the use of oak staves or oak chip during fermentation and maturation process of winemaking. This is a much more budget option and is commonly used for commercially-focused wines. When a winemaker wants to make a more fruit-driven style of wine, old barrels are used. This allows maturation of wine structure and texture without being too oaky. Normally oak flavours disappear after three years of usage, and these barrels are described as being ‘neutral’.