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added note about aerobic Brett starters possibly contributing to THP
There are generally two approaches to handling ''Brettanomyces'' starters. The first is to use a stir plate set to a medium-high RPM with tin foil on top of the flask for 7-8 days, cold crash for a few days, and then decant the beer before pitching the sedimented yeast. The second approach is to use an orbital shaker set to 80 RPM to create a ''semi-aerobic'' environment (this means that the oxygen levels are low, but also not non-existent) for 7-8 days as described in ''The Brettanomyces project'' <ref name="chad_rpm">[http://www.brettanomycesproject.com/dissertation/propagation-and-batch-culture-growth/propagation-methods/ Yakobson, Chad. The Brettanomyces Project. Propagation and Batch Culture Methods. Retrieved 2/18/2015.]</ref>, cold crashing can be skipped, and the entire starter is pitched into the wort. An alternative to the second approach is to use a stir plate on a very low setting so that only a very small "dimple" of a vortex is formed <ref>[https://www.facebook.com/groups/MilkTheFunk/permalink/1168024059892473/?comment_id=1174867645874781&reply_comment_id=1174924805869065&total_comments=1&comment_tracking=%7B%22tn%22%3A%22R9%22%7D Conversation with Mark Trent, Richard Preiss, and Roy Ventullo on MTF regarding creating a semi-aerobic starter without an orbital shaker. 11/06/2015]</ref>. If a stir plate is not available, give the starter an initial dosage of pure O2, and then cover it with foil so that oxygen can slowly diffuse into the starter, and gently agitate as often as possible <ref>[https://www.facebook.com/groups/MilkTheFunk/permalink/1019859158042298/?comment_id=1020313737996840&offset=0&total_comments=24&comment_tracking=%7B%22tn%22%3A%22R6%22%7D Conversation with Nick Impellitteri on MTF in regards to semi-aerobic starters. 2/16/2015.]</ref>.
Oxygen levels are an important factor to consider when deciding which of the above two methods to use for a ''Brettanomyces'' 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>. In addition to acetic acid production, it has been observed that some ''Brettanomyces'' strains grown under aerobic conditions produce THP under anaerobic conditions. See [[Tetrahydropyridine#Brettanomyces|THP]] for details.
This presents a sort of "catch 22" when growing ''Brettanomyces'' in a starter. The brewer must weigh the pros and cons of how much aeration to provide. If the ''Brettanomyces'' is going to be used in a [[100% Brettanomyces Fermentation]], for example, then a stir plate may be the best choice. If the ''Brettanomyces'' 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. ''Brettanomyces'' 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, ''Brettanomyces'' 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.