13,703
edits
Changes
no edit summary
Cartwright et al. (2018) confirmed these results and reported that as little as 12 minutes of steam was enough to eliminate ''Brettanomyces'' in both French and American oak wine barrels that were previously inoculated with ''B. bruxellensis'' for 6 to 7 months. In general, the French oak barrels had larger populations of ''B. bruxellensis'' than the American oak barrels, likely due to American oak being less dense. The staves closest to the bungholes had the largest population of ''B. bruxellensis'' 0-4mm into the wood, likely due to better access to oxygen, but there were also large populations within the bottom staves which were found at deeper levels into the wood (5-9mm deep). Oak barrels with heavy toast levels tended to have higher populations perhaps due to more cracks in the staves or more availability of cellobiose. The French barrels required 12 minutes and the American oak barrels required only 9 minutes at 131°F (55°C) to eliminate all ''B. bruxellensis'' from even the deepest points into the oak where ''B. bruxellensis'' has been found (up to 9mm). Before this was achieved, it took 4 minutes to reach this temperature at 9.5mm into the oak. They could not culture ''Brettanomyces'' from the oak even after incubation of stave cross-sections in WRM for 60 days. Hot water was also reported by the same research group to effectively eliminate ''Brettanomyces'' from oak barrels, although it took longer (70°C for 30 minutes or 80°C for 20 minutes). The researchers expressed the opinion that the effect of heat treatment on barrel quality needs to be researched. 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 with 12 to 20 minutes of 131°F (55°C) to 140°F (60°C) of steam pasteurization <ref name="Cartwright_2018" /><ref>[https://search.informit.com.au/documentSummary;dn=008738882146548;res=IELHSS Zachary Cartwright and Charles Edwards. "Wine maturation: What can a winemaker do about 'Brettanomyces bruxellensis' present in oak barrels?" Wine & Viticulture Journal. Volume 34 Issue 4 (Spring 2019).]</ref><ref>[https://www.journals.ac.za/index.php/sajev/article/view/3008 Edwards, C.G. and Cartwright, Z.M. (2019) Applicatio nof heated water to reduce populations of Brettanomyces bruxellensis present in oak barrel staves. Sth. Afr. J. Enol. Vitic. 40:1-8.]</ref>.
Swaffield and Scott (1995) found that the 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 bacteria can grow deeper than 8 mm into oak, 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>. Additionally, some strains of ''Lactobacillus '' can survive higher temperatures that ''Brettanomyces''; see [[Lactobacillus#Tolerance_of_Extreme_Temperature|''Lactobacillus'']] for more information. Other yeast species may also be more resistant to heat sanitation in barrels, specifically ''Debaryomyces hansenii'', ''Candida parapsilosis'', ''Candida ishiwadae'' have been found to be more resistant to steam treatment in wine barrels than ''B. bruxellensis'' <ref>[https://link.springer.com/article/10.1007/s00217-011-1523-8#citeas Guzzon, R., Widmann, G., Malacarne, M. et al. Survey of the yeast population inside wine barrels and the effects of certain techniques in preventing microbiological spoilage. Eur Food Res Technol 233, 285–291 (2011). https://doi.org/10.1007/s00217-011-1523-8.]</ref>.
Ozone has been shown to be an effective way to kill ''Brettanomyces'' that is buried in the wood of oak barrels (it has been found to burrow as deeply as 8 mm into oak barrels), but the ozone must be applied for an adequate time to allow for the ozone to diffuse into the oak. The amount of time needed to completely kill ''Brettanomyces'' living within barrels with ozone is not known, but it was found that 30 minutes of exposure to 40 mg/m<sup>3</sup> ozone concentration was not enough time and the presence of organic material interferes with the ozone's ability to kill <ref>[https://www.researchgate.net/profile/Raffaele_Guzzon/publication/225890726_Survey_of_the_yeast_population_inside_wine_barrels_and_the_effects_of_certain_techniques_in_preventing_microbiological_spoilage/links/5472f6170cf2d67fc035d45f.pdf Survey of the yeast population inside wine barrels and the effects of certain techniques in preventing microbiological spoilage. Guzzon, Raffaele & Widmann, Giacomo & Malacarne, Mario & Nardin, Tiziana & Nicolini, Giorgio & Larcher, Roberto. 2011.]</ref>. The concentration of ozone is known to be a more important killing factor than time, therefore some recommend filling the barrel with liquid ozone, or rinsing with hot water first to open the pores of the wood and then rinsing with ozone liquid <ref>[https://www.facebook.com/groups/MilkTheFunk/permalink/1860978937263645/?comment_id=1861100817251457&comment_tracking=%7B%22tn%22%3A%22R5%22%7D Nate Ferguson of Escarpment Labs. Milk The Funk Facebook thread about using ozone to sanitize barrels. 10/24/2017.]</ref><ref>[https://www.winesandvines.com/features/article/109491/Barrel-Washing-Protocols Wines & Vines website. "Barrel-Washing Protocols". Jan 2013. retrieved 10/24/2017.]</ref>.