13,602
edits
Changes
no edit summary
Oxygen levels are an important factor to consider when deciding which method to use for a ''Brett'' starter. ''Brettanomyces'' creates acetic acid in the presence of oxygen, potentially leading to higher levels of ethyl acetate, which is considered an off flavor in higher amounts. As the amount of oxygen increases, cell growth increases, but so does acetic acid production. The amount of acetic acid produced is species/strain dependent, so some strains may benefit from more aeration without having the negative effect of creating too much acetic acid. Other strains may need a less aerobic starter (''semi-aerobic'') in order to produce the highest cell count with minimal acetic acid <ref>[http://www.ncbi.nlm.nih.gov/pubmed/12655458 Brettanomyces bruxellensis: effect of oxygen on growth and acetic acid production. Aguilar Uscanga, Délia1, and Strehaiano. 2003.]</ref><ref>[http://onlinelibrary.wiley.com/doi/10.1002/(SICI)1097-0010(199712)75:4%3C489::AID-JSFA902%3E3.0.CO;2-9/abstract Role of oxygen on acetic acid production by Brettanomyces/Dekkera in winemaking. Maurizio Ciani and Luisa Ferraro. April 1999.]</ref><ref>[http://link.springer.com/article/10.1023%2FA%3A1014927129259 Acetic acid production by Dekkera/Brettanomyces yeasts. S.N. Feer. April 2002.]</ref>.
This presents a sort of "catch 22" when growing ''Brett'' in a starter. The brewer must weigh the pros and cons of how much aeration to give. If the ''Brett'' is going to be used in a [[100% Brettanomyces Fermentation]], for example, then a stir plate may be the best choice. If the ''Brett'' is instead being pitched in secondary with the intention of long aging, then having a high cell count isn't as necessary and the risk of adding more acetic acid/ethyl acetate to an aging beer is greater. If a lot of acetic acid is produced during the starter, it is advised to cold crash and decant the starter. ''Brett'' can have a difficult time flocculating and settling out, even when cold crashed. The brewer may need to allow a few days for the cells to fully sediment <ref>[https://www.facebook.com/groups/MilkTheFunk/permalink/1099473923414154/?comment_id=1099522943409252&offset=0&total_comments=25&comment_tracking=%7B%22tn%22%3A%22R%22%7D Conversation with Richard Preiss of Escarpment Yeast Labs on MTF. 6/26/2015.]</ref>. Additionally, ''Brett'' that is cold crashed may be slower to begin fermentation. If the brewer believes that the amount of acetic acid produced was insignificant, then cold crashing can be skipped and the entire starter can be pitched.
Current yeast pitching calculators for brewers are not adequate for determining ''Brett'' starter sizes due to the cell densities of ''Brett'' per mL of wort being 3-6x the cell densities of ''Sacch''. For example, a given ''Sacch'' strain may reach a cell density of 130 million cells per mL in a 1.040 wort (different ''Sacch'' strains can have different cell densities as well, although they are a lot lower than ''Brett'' overall). ''Brett'' cell densities have been reported to be 600 to 885 million cells per mL in 1.040 wort <ref name="Yakobson_Propagation">[http://www.brettanomycesproject.com/dissertation/propagation-and-batch-culture-growth/propagation-results/ Yakobson, Chad. The Brettanomyces Project. Propagation and Batch Culture Results. Retrieved 2/17/2015]</ref><ref name="MarkTrent">[https://www.facebook.com/groups/MilkTheFunk/permalink/1114254011936145/ Conversation with Mark Trent and Lance Shaner on MTF regarding Brett pitching rates. 07-21-2015.]</ref>. Since yeast calculators are based off of ''Sacch'' cell densities, using one of these tools for ''Brett'' starters will create an unexpectedly high cell count. There is not currently enough data to accurately determine starter volumes for ''Brett'', particularly because each strain and species has a different maximum cell density per mL of wort. However, pitching around 500-600 mL of a ''Brett'' starter for 5 gallons of 1.060 SG wort will achieve a pitching rate that is similar to lager yeast pitching rates, which has been recommended for [[100% Brettanomyces Fermentation]]. [[Omega Yeast Labs]] is currently working on a project to create a more accurate ''Brett'' pitching rate calculator (it will also contain pitching rate calculations for specific strains of ''Sacch'', which is something that current yeast pitching calculators do not include) <ref name="MarkTrent"></ref>.