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added link back to turbid mashing for fermentation info
==Fermentation of Spontaneous Beers==
Producers of spontaneously fermented beer typically do not oxygenate their wort <ref name="Beer Temple interview with De Garde"></ref> (~27 minutes in). Visual signs of fermentation (CO2 production, krausen, bubbles, etc.) generally takes 4-7 days, although we have seen reports of up to two weeks <ref name="howat_comeandbrewit">[http://comeandbrewit.libsyn.com/2016/page/2/size/25 "Episode 34- Sour Beer 102", Come and Brew It podcast. Interview with James Howat from Black Project Spontaneous Ales. 01/07/2016 (~40 minutes in).</ref><ref>[https://www.facebook.com/groups/MilkTheFunk/permalink/1183899281638284/ Conversation with Caleb Buck on MTF about spontaneous fermentation. 11/24/2015.]</ref><ref>[https://www.facebook.com/groups/MilkTheFunk/permalink/1189818124379733/?comment_id=1194393553922190&comment_tracking=%7B%22tn%22%3A%22R3%22%7D Conversation on MTF with Dustin Carver on how long his spontaneous fermentation took to start. 12/14/2015.]</ref><ref>[https://www.facebook.com/groups/MilkTheFunk/permalink/1213062435388635/?comment_id=1215511598477052&comment_tracking=%7B%22tn%22%3A%22R2%22%7D Conversation on MTF with Mark B. Fry on how long spontaneous fermentation took for him. 01/13/2016.]</ref>. Traditional producers conduct fermentation for a [[File:Homebrew spontaneous fermentation.jpeg|200px|thumb|right|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 (see [[Turbid_Mash#Carbohydrate_Composition_and_Utilization_Through_Fermentation|turbid mashing]] for more) <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>. Extended aging in the same vessel as fermentation does not present the same sort of autolysis problems that may be found in 'clean' beers aged for long periods of time on the yeast cake. There are some ideas for why this is the case, such as the extended activity of other microbes taking up autolysis products. It is also possible that the influence of autolysis is found, but that they are expressed differently in these sorts of beers and some say that the autolysis character is an important component of the beers <ref>[http://www.thebrewingnetwork.com/the-sour-hour-episode-9/ Rudy Ghequire from Rodenbach on the Sour Hour]</ref> (~28 minutes in).
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.