Changes

Sanitizing barrels that are infected with ''Brettanomyces'' or other beer/wine spoilers is notoriously difficult, and some believe it to be impossible. While two previous studies ([http://www.ajevonline.org/content/62/4/519 Schmid et al. 2011] and [http://www.ccsenet.org/journal/index.php/jfr/article/view/24315 Barata et al. 2013]) found that steam was not effective at sanitizing oak, these studies have had their experimental designs criticized by other presumably better designed studies ([https://www.ncbi.nlm.nih.gov/pubmed/25989358 Fabrizio et al. 2015] and [http://www.ajevonline.org/content/early/2018/05/23/ajev.2018.18024 Cartwright et al. 2018]) that found that steam is indeed an effective way to kill all ''Brettanomyces'' in oak barrels that previously held ''B. bruxellensis'' inoculated wine. For example, Schmid et al. (2011) inoculated oak chips with nutrient broth instead of using barrels that represented real world conditions, and Barata et al. (2013) only applied steam for 10 minutes <ref name="Cartwright_2018">[http://www.ajevonline.org/content/early/2018/05/23/ajev.2018.18024 Reduction of Brettanomyces bruxellensis Populations from Oak Barrel Staves Using Steam. Zachary M. Cartwright, Dean A. Glawe, Charles G. Edwards. 2018. DOI: 10.5344/ajev.2018.18024.]</ref>. Fabrizio et al. (2015) proposed that the most effective and preferred method is to heat the inside of the oak barrel to at least 140°F (60°C) for 20 minutes with hot water or steam. This was found to be an effective way of killing ''Brettanomyces'' that was found growing as deep as 8 mm within the wood of 3-year old barrels infected with ''Brettanomyces''. Note that this might not be hot enough to kill other heat tolerant microbes, however, these heat tolerant species tend not to be able to survive in beer. Treatments that are higher in temperature and longer should be fine with steam, however, if hot water is used then the longer the water is exposed to the barrel the more character from the barrel that gets removed <ref>[https://www.ncbi.nlm.nih.gov/pubmed/25989358 Heat inactivation of wine spoilage yeast Dekkera bruxellensis by hot water treatment. Fabrizio, Vigentini, Parisi, Picozzi, Compagno, Foschino. 2015.]</ref><ref name="Agnolucci_2017">[https://link.springer.com/article/10.1007/s11274-017-2345-z Brettanomyces bruxellensis yeasts: impact on wine and winemaking. Monica Agnolucci, Antonio Tirelli, Luca Cocolin, Annita Toffanin. 2017.]</ref>. Cartwright et al. (2018) confirmed these results and reported that as little as 12 minutes of steam was enough to pasteurize both French and American oak wine barrels that were inoculated with ''B. bruxellensis'' for 6 to 7 months, with the French barrels requiring 12 minutes and the American oak barrels requiring only 9 minutes at 131°F (55°C). They could not culture ''Brettanomyces'' from the oak even after incubation of stave cross-sections in WRM for 60 days. Although it has been reported that extensive heating can destroy desirable oak flavor compounds such as guaiacol, 4-methylguiaicol, furfural, lactones, eugenol, and vanillin, degradation of these compounds requires temperatures between 248°F (120°C) and 365°F (185°C) for 1 to 6 hours, so significant degradation of desirable oak flavor compounds is not expected to occur at 12 to 20 minutes of 131°F (55°C) to 140°F (60°C) of steam pasteurization <ref name="Cartwright_2018" />.

Swaffield and Scott (1995) found the yeast and lactic acid bacteria belonging to the genre ''Lactobacillus'', ''Pediococcus'', and ''Leuconostoc'' that were in cider penetrated oak blocks up to 1.25 cm after 9 weeks of being submerged 1 mm into the cider, so it is possible that yeast and bacteria can broww deeper than 0.8 mm into wood, although these oak cubes were made from virgin oak vats and might not accurately reflect what would be found if these same microbes were inoculated in oak barrels <ref>[https://www.asbcnet.org/publications/journal/vol/Abstracts/bc1995a22.htm Existence and Development of Natural Microbial Populations in Wooden Storage Vats Used for Alcoholic Cider Maturation. C. H. Swaffield and J. A. Scott. 1995. DOI: 10.1094/ASBCJ-53-0117.]</ref>.