Changes

Yeast that fails to bottle condition sour beer may not be due to death of the cells. Rogers et al. <ref name="rogers2016"></ref> published a study that found that yeast used to bottle condition a sour beer at [http://uplandbeer.com/ Upland Brewing Co.] was still ~80% viable after two weeks, but the surviving cells were small and unbudded, indicating that they ceased growing and entered the stationary phase . This effect has been referred to as "terminal acid shock" <ref name="rogers2016"></ref>.

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 they are able to bottle condition sour beer. 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 both 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 the combination of stress from high alcohol, acetic acid, low nutrients, low oxygen, and tannins from fruit. This effect has been referred to as "terminal acid shock". Re-hydrating dried yeast may also lead to difficulties carbonating acidic and high ABV (8%+) sour beer due to the stress of desiccation and re-hydration on the yeast <ref name="rogers2016"></ref>.

Rogers et al. found an easy solution to carbonating very sour, high ABV beers by acclimating the yeast to the sour beer. Growing the yeast in YPD plus lactic acid plus ethanol was not enough to acclimate the yeast and reliably carbonate a highly acidic, alcoholic (8% ABV) beer. However, by growing the yeast first in a blend of YPD that was diluted with the sour beer itself in a 1:1 ratio, they found that the yeast was both CBC-1 and WLP715 were then able to carbonate the sour beer(WlP001, WY1056, WY2007, and WLP300 were not given this treatment). This was explained as being a way of "pre-adapting" the yeast to the harsh conditions of the 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 and yeast nutrients (Fermaid K and DAP, for example) <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>.