This varies with base style, though is often darker than the unadulterated base beer style, particularly if toasted oak and/or whiskey barrels are used.
Wood and barrel-aged beer is a beer that has been aged over a period of time in wooden barrels or uses wood-based additives. It can be any ale, lager, or hybrid beer.
Ageing in wooden barrels imparts the characteristic qualities of the wood and/or the flavour profile of the beverage previously stored in the barrel (such as wine or whiskey). Instead of wooden barrels, it is possible to use wood-based additives, such as wood chips, oak essence, etc.
The flavour characteristics of the beer vary depending on the barrel used and the style of beer brewed. Oak barrels are most commonly used, which can impart notes of vanilla and caramel to the beer. It is common to age beer in barrels that previously held a stronger alcoholic beverage, such as whiskey. This type of beer is often valued for its complex flavour and unique character.
Before the introduction of stainless steel and aluminium, wooden barrels were the primary means for storing and transporting beer. At that time, a wooden barrel was simply a container, and brewers did not want it to impart any flavour characteristics to the beer. Rather, they intentionally tried to prevent this by cleaning the barrels with boiling water and hydrochloric acid.
With the widespread adoption of stainless steel, wood practically disappeared from the beer world. Wooden barrels continued to be used only for some speciality beers, such as lambic beers.
Today, craft brewers, especially in the United States, have brought wood back into the brewery. Now, a wooden barrel is no longer just a container; brewers want the wood to influence the flavour and aroma of the beer. This has become a valued (and generally pretty expensive) beer style.