Changes

===Thiols===

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 β-lyase activity is expressed by strains of ''Saccharomyces cerevisiae'' that have the ''IRC7'' gene. This activity takes place within the yeast cells which uptake the bound thiol precursors and then expel the free thiols. Most industrial brewing and wine strains of ''S. cerevisiae'' do not have a functional version of this gene due to a lack of selective pressure. Even in strains with a functional version of the ''IRC7'' gene, the expression of the gene is repressed in nitrogen rich substrates such as wort <ref>[https://www.masterbrewerspodcast.com/227 Dr. Laura Burns and Lance Shaner. MBAA Podcast Episode 227 Interview. 10/18/2021. Retrieved 02/10/2023.]</ref>(~4 mins in). 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 <ref name="Svedlund_2022" />. So far, science has found that these include the volatile thiols:

* 3-mercaptopentanol (3MP; also referred to as 3-sulfanylpentan-1-ol, 3SP)

Acetylation (acetate) variations: