Changes

''Saccharomyces'' species and individual strains have a wide range of tolerance to low pH and lactic/acetic acid concentrations, which have been identified as stressors for yeast fermentation. For ideal fermentation conditions for ''S. cerevisiae'', lactic acid should not exceed 0.8%, acetic acid should not exceed 0.5%, and wort should not fall below 4.0 pH. Since pH is on a log-based scale, even small differences in pH (In Progressespecially below 3.5)can make a large impact on whether or not a given yeast strain is able to ferment. This obviously presents a challenge to brewers when [[Sour Worting]] or [[Packaging|naturally carbonating with yeast]] for sour beers <ref name="rogers2016">[http://www.sciencedirect.com/science/article/pii/S0740002016301605 Terminal acidic shock inhibits sour beer bottle conditioning by Saccharomyces cerevisiae. Cody M. Rogers, Devon Veatch, Adam Covey, Caleb Staton, Matthew L. Bochman. 2016.]</ref>.

''Saccharomyces'' species and individual strains have a wide range Yeast that fails to bottle condition sour beer may not be due to death of tolerance to low pH and lactic/acetic acid concentrations, which have been identified as stressors for yeast fermentationthe cells. For ideal fermentation conditions for ''S. cerevisiae'', lactic acid should not exceed 0.8%, acetic acid should not exceed 0.5%, and wort should not fall below 4Rogers et al.0 pH. This obviously presents a challenge to brewers when [[Sour Worting]] or [[Packaging|naturally carbonating with yeast]] for sour beers <ref name="rogers2016"></ref> published a study that found that yeast used to bottle condition a sour beer at [http://www.sciencedirectuplandbeer.com/science/article/pii/S0740002016301605 Terminal acidic shock inhibits sour beer bottle conditioning by Saccharomyces cerevisiaeUpland Brewing Co. Cody M. Rogers] was still ~80% viable after two weeks, Devon Veatchbut the surviving cells were small and unbudded, Adam Covey, Caleb Staton, Matthew L. Bochman. 2016.]indicating that they ceased growing and entered the stationary phase <ref name="rogers2016"></ref>.

Yeast As stated previously, lactic acid and low pH are identified as stressors for yeast, and can affect their ability to carbonate sour beer. Some strains tested display an ability to grow in higher lactic acid concentrations, while others do not, but this does not indicate that fails they are able to bottle condition sour beer may . For example, WLP001 and WY1056 do not grow well in YPD dosed with lactic acid, where as Lallemand CBC-1 ("Cask & Bottle Conditioned Beer Yeast") can still grow at a pH of 3. WY2007 and WLP300 grow well in moderate levels of lactic acid, but not once the pH gets down to 3. WLP715 Champagne Yeast grows fine in a pH of 3 (although lag time is effected). However, despite being able to grow in YPD with lactic acid dosages, CBC-1 and WLP715 failed to carbonate an 8% ABV sour beer that had a comparable pH to the pH of the YPD plus lactic acid mediums. It is suggested that this might be due to death the combination of the cellsstress from high alcohol, acetic acid, low nutrients, low oxygen, and tannins from fruit. This effect has been referred to as "terminal acid shock". Rogers et al. Re-hydrating dried yeast may also not carbonate a highlight acidic and high ABV (8%+) beer due to the stress of desiccation and re-hydration on the yeast <ref name="rogers2016"></ref> published . Rogers et al. found an easy solution to carbonating very sour, high ABV beers. Growing the yeast in YPD plus lactic acid plus ethanol was not enough to reliably carbonate a study highly acidic, alcoholic (8% ABV) beer. However, they found that by growing the yeast first in a solution of YPD diluted with the sour beer itself in a 1:1 ratio, they found that the yeast used were then able to bottle condition a carbonate the sour beer at [http://uplandbeer.com/ Upland Brewing Co.] This was still ~80% viable after two weeks, but explained as being a way of "pre-adapting" the yeast to the surviving cells were small and unbudded, indicating that they ceased growing and entered harsh conditions of the stationary phase sour beer <ref name="rogers2016"></ref>. It has been speculated that brewers without access to YPD could grow the conditioning yeast in sour beer diluted with DME wort with yeast nutrients (Fermaid K) and DAP <ref>[https://www.facebook.com/groups/MilkTheFunk/permalink/1259063934121818/?comment_id=1262875587073986&reply_comment_id=1263142900380588&comment_tracking=%7B%22tn%22%3A%22R9%22%7D Conversation with Richard Preiss and Tamir Danon on acclimating yeast to sour beer for conditioning on MTF. 03/24/2016.]</ref>.