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]). 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>. In contrast, Fabrizio et al. (2015) and Cartwright et al. (2018) found that it is possible that steam is an effective way to kill all ''Brettanomyces'' in oak barrels that previously held ''B. bruxellensis'' inoculated wine. 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 Steam treatments that are higher in temperature and longer should be fine with steam, not present any concerns; however, if hot water is used instead of steam then the longer the water is exposed to the barrel the more character from the barrel that gets removed by the water <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 eliminate ''Brettanomyces'' in both French and American oak wine barrels that were previously inoculated with ''B. bruxellensis'' for 6 to 7 months, with the . The French barrels requiring required 12 minutes and the American oak barrels requiring required 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 with 12 to 20 minutes of 131°F (55°C) to 140°F (60°C) of steam pasteurization <ref name="Cartwright_2018" />.

Other non-thermal methods of pasteurizing barrels have been explored. Microwave treatment at 3000 W for 3 minutes of barrels filled with water reduced populations by 35% in French oak barrels and 67% in American oak barrels up to the 8 mm depth in which ''Brettanomyces'' can survive within the wood of oak barrels. High power ultrasonics (17 W/L for 3 minutes) applied to barrels filled with 60°C water kills all ''Brettanomyces'' up to 4 mm within the oak, but has limited penetration of the wood passed 4 mm <ref name="Cartwright_2018" />. The use of sulfur dioxide (SO₂) has been shown to inhibit ''Brettanomyces'' and other microbes, ; however, ''Brettanomyces'' cells that are exposed to sulfur dioxide can enter a state known as "viable but nonculturable" (VBNC) meaning that they cannot complete cell division (grow) but can still maintain a small amount of metabolism, and can be revived when the sulfur dioxide is no longer in their environment. Therefore, sulfur dioxide is not an effective way to completely sanitize oak barrels (although it has been used successfully to store non-infected barrels). See [[Quality_Assurance#VBNC_In_Yeast|VBNC in Yeast]] for more information.