Just what are thiols? And just how can we debunk them? In this article Alix Blease from Lallemand highlights the key findings in recent papers from the field and breaks down some of the scientific jargon with the aim that you are able to apply these findings to your own beer.
When I started at Lallemand 3 years ago, the first article I wrote for the Brewers Journal answered the questions; what are thiols and how do you maximise them in your brewing process? If you’re sitting reading this, waiting for your wort to boil and thinking to yourself “what is she talking about; what is a thiol?” I invite you to go back and take a read of that first article, available on the Brewers Journal website (Winter Report 2023).
Since then, the research of these poorly understood compounds has been advanced by Thomas Shellhammer (Oregon State University) and the team at Lallemand. Over the past year there have been several key papers published on the topic of thiols and biotransformation in beer.
These papers focus on influential factors which affect the level of thiols in a pint, for example, yeast strain, fermentation temperature, free amino nitrogen (FAN) level and the impact of dry hopping. This research has revealed more about the pathways through which yeast free the bound, non-aromatic, thiols in beer. It is worth noting at this point that these papers are by no means exhaustive, and there is still much research to be done in this area of beer flavour and aroma.
In this article I hope to highlight the key findings in these papers and breakdown some of the scientific jargon with the aim that you are able to apply these findings to your own beer.
Firstly, let’s examine the influence of fermentation temperature and yeast strain selection on the free thiol concentration in finished beer. Comparisons were made between four ale strains; Nottingham, Verdant, BRY-97 and London, as well as one lager strain, Diamond. An identical wort, with Cascade hops added hot-side, was fermented with each of the five yeast strains at 15, 22 and 30°C.
The highest level of free thiols was produced by Diamond yeast at 30°C. However, when analysed by a panel of 25 experienced tasters the beers produced using the ale strains at the warmer temperatures of 22-30°C were described as the most tropical.
Fermenting using Diamond at 30°C may release more free thiols but it also creates a lot of other undesirable sulphur compounds, which in sensory analysis can mask the positive tropical notes of thiols.
“High thiol concentrations alone did not guarantee enhanced tropical character,emphasising the critical role of synergistic interactions between thiols and other aroma-active compounds such as esters and terpenoids”
Wort FAN level also had an impact on the production of free thiols. In this experiment the base worts had varying FAN levels of 110, 240, 360 mg/L and were again hopped hot-side with Cascade. The same yeast strains selected, with one addition, an ale yeast, Verdant, which had been genetically modified to inactivate the ICR7 gene. ICR7 is thought to be the gene in yeast responsible for encoding the β-lyase enzyme. β-lyase is an enzyme responsible for cleaving bound-thiols resulting in free thiols.
Lower FAN levels; 110-240 mg/L were responsible for the highest release of thiols. However, in sensory studies higher FAN levels were determined to be the most tropical, due to the higher level of ester production. Interestingly, the IRC7-knockout Verdant maintained a similar level of thiol production to the regular Verdant yeast, suggesting alternative gene or enzymatic pathways for thiol release.
“Nottingham and Diamond exhibited robust performance and thiol release across FAN treatments, whereas strains like BRY-97 and Verdant IPA showed greater sensitivity to nitrogen level, including increased off-flavour potential at FAN extremes.”
In the most recent paper the thiol, 3-sulfanylhexan-1-ol (3SH) in its bound form was quantified throughout the brewing process and the resulting free thiol, responsible for grapefruit and passionfruit aromas, was measured in each of the finished beers. Four fermentation profiles were analysed (see diagram). Two were fermented with Verdant, and two with Diamond. For each yeast strain analysed one of the fermentations was dry hopped and the other was not.
All of the profiles had the same amount of Cascade hops added hot-side at two addition points, 1.9g/L at the start of boil and 3 g/L in whirlpool. It was found that 91% of the available bound-thiols in the hops were transferred into the wort. This is a high transfer efficiency and indicates that a large percentage of the bound-thiols are not driven off during the boil.
In both the dry-hopped and non dry-hopped beers fermenting with Diamond resulted in 1.6x higher levels of free-thiols than the beers made with Verdant. In both dry-hopped beers, made with Diamond and Verdant the free-3SH levels were 2.1x higher than their non dry-hopped counterparts.
However, it is worth noting that the free-3SH in all the beers accounted for less than 1% conversion of the available bound-precursor and around half of all the available precursor compounds remained unconverted in the final beer. Therefore, the availability of bound-precursors is not a limiting factor, the main influencing factors are the choice of yeast strain and the addition time of the hops.
“The results emphasize that the 3SH generation is not limited by precursor supply but by the metabolic competence of the yeast and the timing of hop additions.”
Cecile Chenot, Ronald Samia, and Thomas H. Shellhammer Journal of Agricultural and Food Chemistry 2026 74 (10), 8627-8635
Ronald Samia, Avi Shayevitz, Tobias Fischborn & Thomas H. Shellhammer (14 Aug 2025): Wort Nitrogen and Yeast Strain Drive Thiol Release, Flavor Expression, and Fermentation Performance in Beer, Journal of the American Society of Brewing Chemists,
Ronald S. Samia, Cecile Chenot, Avi Shayevitz, Tobias Fischborn & Thomas H. Shellhammer (26 Dec 2025): Interactions Between Fermentation Temperature and Yeast Strain: Impacts on Polyfunctional Thiol Release and Beer Aroma, Journal of the American Society of Brewing Chemists
