What is the term for the secondary fermentation process in a barrel?

Barrel aging is the term specifically used to describe the secondary fermentation process that occurs in a barrel. This process allows beer to develop complex flavors and characteristics that are influenced by the wood of the barrel, as well as any residual flavors from previous liquids that have been stored in it, such as whiskey, wine, or rum.

During barrel aging, the beer can undergo both fermentation and maturation. The interaction between the beer and the wood can impart flavors like vanilla, caramel, and spices, while also allowing for micro-oxidation, which can enhance the mouthfeel and overall character of the beer. This aging process often lasts for several months to years, significantly contributing to the final product's taste profile.

The other options relate to different concepts. Biodynamic aging refers to a holistic approach to farming that focuses on maintaining the ecosystem, and while it might influence the ingredients used in brewing, it isn’t a fermentation term. Conditioning typically refers to the process of allowing beer to mature or clarify before consumption, but it does not specifically imply the use of barrels. Oxidation, on the other hand, is a chemical reaction that can occur during aging, but it is not the same as barrel aging and can sometimes lead to undesirable flavors if not controlled.