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Sulfur-based compounds bound to a hydrogen atom known as ''thiols'' have also been shown to be produced by yeast fermentation from the hop derived precursors cysteine or glutathione via yeast β-lyase activity . This activity takes place within the yeast cells which uptake the precursors. The cysteine and glutathione precursors are also found in malt, hops, grapes and rice, with levels varying greatly depending on varieties of the plants. In addition to some strains of ''Saccharomyces cerevisiae'' that express the genes to produce thiols, strains of the yeasts ''Metschnikowia pulcherrima'', ''Torulaspora delbrueckii'', ''Lachancea thermotolerans'', ''Candida zemplinina'', and the bacteria ''Lactobacillus plantarum'' have also been found to produce thiols <refname="Svedlund_2022">[https://link.springer.com/article/10.1007/s00253-022-12068-w Svedlund, N., Evering, S., Gibson, B. et al. Fruits of their labour: biotransformation reactions of yeasts during brewery fermentation. Appl Microbiol Biotechnol 106, 4929–4944 (2022). https://doi.org/10.1007/s00253-022-120.]</ref>. So far, science has found that these include the volatile thiols : * 3-mercaptohexan-1-ol (3MH; also referred to as 3-sulfanylhexan-1-ol, 3SH; ''tropical fruit'')* 4-mercapto-4-methylpentan-2-one (4MMP; also referred to as 4-methyl-4-sulfanylpentan-2-one, 4MSP; ''blackcurrant'') * 3-sulfanyl-4-methylpentan-1-ol (3S4MP; ''grapefruit'')* 3-mercaptopentanol (3MP; also referred to as 3-sulfanylpentan-1-ol, 3SP) and Acetylation (acetate) variations:* 3-sulfanyl-4-methylpentyl acetate (3S4MPA; ''passionfruit'', ''grapefruit'')* 3-mercaptohexyl acetate (3MHA)Typically, in beer and wine, the amount of free thiols that are formed from these precursors is less than 1%, perhaps due to poor activity of β-lyase activity in acidic media and inhibition by polyphenols. These However, these thiols were found in beers dry hopped separately with Amarillo, Hallertau Blanc, and Mosaic hop varieties. The amounts of these two thiols were higher than expected based on the content of these thiols in the hops alone <ref name="Cibaka_2016" />. Dry hopping temperature plays a role, with with 18-24°C being optimum for 3Mh and 3MP, and 28°C being optimum for 3S4MP. Mash hopping can potentially increase thiols, while using copper in the brewing or winemaking process can reduce them <ref name="Svedlund_2022" />. [[Omega Yeast Labs]] has bioengineered a yeast strain called [https://omegayeast.com/news/cosmic-punch-new-thiol-boosting-strain Cosmic Punch™ (British V OYL-011)] to produce significant amounts of thiols from hops and malted grains. [https://berkeleyyeast.com/available-yeast-strains/ Berkeley Yeast] also offers bioengineered yeast strains that produce thiols. See also this [https://www.facebook.com/groups/MilkTheFunk/permalink/1373899592638251/ MTF thread speculating on how ''Brettanomyces'' might produce thiols].