Changes

Headspace and fermenter size are also concerns when it comes to aging beer with living ''Brettanomyces''. This includes sour beers, [[Brettanomyces_and_Saccharomyces_Co-fermentation|non-sour beers with ''Saccharomyces'' and ''Brettanomyces'']], and [[100%25_Brettanomyces_Fermentation|100% ''Brettanomyces'' beers]] that are aged. The larger the headspace, the more air will be sucked in when a vacuum occurs. The smaller the fermenter, the more headspace becomes a problem. Smaller vessels, in general, have a larger surface area to volume ratio. Therefore, they have more potential for exposure to oxygen. A large headspace in a smaller vessel exacerbates this problem, therefore it is advised to top up small fermenters and flush them with CO<sub>2</sub?> after primary fermentation or if significant evaporation occurs during aging. For example, a 1-gallon jug should be filled all the way to the neck if possible. A 5-gallon carboy could also be filled to the neck, but a little more headspace is permissible since it is a larger volume. Barrels are porous and the liquid inside them slowly evaporates. Some brewers combat this by topping up their barrels on a regular basis; this also helps keep the top staves from drying out (higher humidity can help limit evaporation; see the [[Barrel#Using_Barrels_for_fermentation_and.2For_aging|Barrel]] page).