13,590
edits
Changes
no edit summary
Although ''Brettanomyces'' is capable of producing APY from L-ornithine <ref name="Grbin_2007" />, the amount produced is much less than that of LAB and high amounts of L-ornithine are required. In wine, there isn't enough L-ornithine present to production significant amounts of APY from L-ornithine. Therefore, the presence of APY (which is much easier to detect aromatically than ATHP) indicates a bacterial contamination in wine (it is unknown if this applies to beer) <ref name="Snowdon"></ref>.
The presence of the "mousy off-flavor" caused by forms of THP appears to be temporary in beer. Although not much is known about the degradation or metabolic breakdown of ATHP/ETHP, it tends to age out of beer after 2-6 months. Since the odor/taste threshold for ETHP is much higher than ATHP, and ATHP appears to be metabolized into ETHP by ''Brettanomyces'' over time, this may be one of the mechanisms by which the mousy off-flavor ages out of beer. The possibility of ETHP breakdown is not mentioned in any studies that we know of, although Moulis et al. (2023) reported that for organisms that produced ETHP, there was always a 1:10 ratio between ETHP/ATHP or ETHP/APY, suggesting that this ratio might be governed by the chemistry of the media used and/or the [https://en.wikipedia.org/wiki/Reduction_potential reduction potential] <ref name="Moulis_2023" />. Another unknown is why does ''Brettanomyces'' produce ATHP shortly after kegging and force carbonating a beer that has reached final gravity. The most likely cause is oxygen pick up during the kegging process. Pitching fresh ''Saccharomyces'' at bottling/kegging time and naturally carbonating the beer with sugar has reportedly reduced mousy off-flavor detection, perhaps because ''Saccharomyces'' metabolizes both the oxygen and sugar faster than ''Brettanomyces''.
===Lactic Acid Bacteria===