Changes

Sour beer should be aged in an environment that minimizes high temperatures and exposure to oxygen. Avoid temperatures over 85°F (29.5°C) and under 55°F (13°C). Drastic temperature fluctuations and changes in atmospheric pressure will cause a vacuum inside of the fermentation vessel causing water airlocks to "suck back" air into the fermenter. This could potentially contribute to [[Acetic Acid]] and [[Ethyl acetate]] (nail polish aroma in high concentrations) production by ''Brettanomyces'', and these off-flavor metabolites are considered permanent. Filling the carboy to the neck or topping up carboys or barrels after primary fermentation will also help minimize the surface area of the beer that can be exposed to air. Topping up and flushing with CO₂ might also help reduce the risk of mold growth on any krausen material that has dried on the sides of the fermentation vessel after primary fermentation. Avoid oversampling the beer (once every 3 months at the very most). One way ventilated silicone bungs can be used for barrels or other waterless type airlocks (such as the [http://www.better-bottle.com/products_master.html BetterBottle "DryTrap"] or kegs with a [http://seanterrill.com/2015/06/25/build-a-better-spunding-valve/ spunding valve]; see also [[Sanke Fermenter]]) that allow gases to escape the fermenter but not enter from the environment, and [https://www.reddit.com/r/Homebrewing/comments/beolwv/spunding_system_for_my_sour_program/ this Reddit post on a daisy-chained spunding valve with corny kegs]. Topping up barrels with fresh beer every 3-6 months might help reduce acetic acid and ethyl acetate, and humidity and temperature control can help reduce evaporation (see [[Barrel#Using_Barrels_for_fermentation_and.2For_aging|Barrel]]). It should also be noted that micro-oxygenation is helpful for creating certain flavors in sour beer, and many homebrewers have reported not having any issues with overexposure to oxygen using water-based airlocks. For example, a small amount of oxygen helps [[Brettanomyces]] growth, and a small level of acetic acid is desirable for the complexity of long -aged sour beers <ref>[https://www.milkthefunk.live/podcast Richard Preiss. Interview on Milk The Funk "The Podcast" Episode #000. 12/13/2017.]</ref> (~30 minutes in). Higher levels of acetic acid are sometimes desirable for [[Flanders Red Ale]] style beers.

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 fermentersand 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 jug carboy could also be filled to the neck, but a little more headspace is permissiblesince 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).