Changes

Producers of spontaneously fermented beer typically do not oxygenate their wort <ref name="Beer Temple interview with De Garde"></ref> (~27 minutes in) and traditional producers conduct fermentation for a [[File:Homebrew spontaneous fermentation.jpeg|right|300px|Spontaneous fermentation beginning in a carboy]]long time period (1-3+ years) in wooden vessels. The long fermentation process allows the different microbes present to carry out their slow metabolism of the complex carbohydrates present in the beer, developing the flavors and acidity associated with spontaneous beers <ref name="Van Oevelen et al., 1976">[http://onlinelibrary.wiley.com/doi/10.1002/j.2050-0416.1975.tb06953.x/abstract Van Oevelen et al., 1976. Synthesis of aroma components during the spontaneous fermentation of lambic and gueuze]</ref> <ref name="Spaepen et al., 1978">[http://onlinelibrary.wiley.com/doi/10.1002/j.2050-0416.1978.tb03888.x/abstract Spaepen et al., 1978. Fatty acids and esters produced during the spontaneous fermentation of lambic and gueuze]</ref>. The wooden fermentation vessels are frequently oak wine barrels in the 220-400 L (58-105 gal) range but other woods such as chestnut are used and the vessels may also be large tuns or foudres holding upwards of 45 HL (about 1200 gal, or about 34 bbl). These barrels provide two primary benefits for the fermentation - they allow a small amount of oxygen permeability and they provide an environment which houses some of the microbes active in the fermentation (notably ''Brettanomyces'', which can penetrate into the wood and in some cases can metabolize compounds present in the wood such as cellobiose, which is produced from toasting of the wood) <ref name="Vinnie on the Session Jan 2010">[http://www.thebrewingnetwork.com/post1940/ Vinnie Cilurzo of Russian River on the Brewing Network's Sunday Session, 17-January-2010]</ref>(~3:22 in). While a controlled micro-oxidation can be beneficial to the beer, too much oxygen exposure can lead to excessive acetic acid and/or ethyl acetate production (either from ''Brettanomyces'' or ''Acetobacter'') <ref name="yakobson1">[http://www.brettanomycesproject.com/dissertation/pure-culture-fermentation/pure-culture-fermentation-discussion/ Yakobson, Chad. Pure Culture Fermentation Characteristics of Brettanomyces Yeast Species and Their Use in the Brewing Industry. Pure Culture Fermentation Discussion. 2011.]</ref>. In addition the barrels may provide flavor and structure from tannins and, in some cases, what they previously held.