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Yeast and Its Effect on Flavour

Dried yeast added to wort in a wooden washback
Dried yeast added to wort in a wooden washback

Yeast makes whisky’s alcohol, but it also helps make its flavour, producing compounds associated with fruity, floral, sulphury and other aromas. The strain chosen matters, especially in new make spirit, the spirit before maturation, but research shows that its performance also depends on how it is supplied and used.[1][3][4]

How yeast creates flavour

During fermentation, yeast converts sugars derived from malt, principally maltose, into ethanol, carbon dioxide and flavour compounds known as congeners. Its flavour contribution comes primarily from producing volatile congeners, including esters and higher alcohols. These are part of fermentation’s output, not something that has to wait for a cask.[1]

Esters are particularly relevant to the fruity aromas discussed in yeast research. Higher alcohols are another important group of fermentation compounds, although the overall aroma cannot be reduced to either group alone. A Heriot-Watt study of 24 commercial dried yeasts recorded alcoholic, fruity, sulphury and sweet notes in the resulting new make spirits.[1][3]

The fermented liquid is called wash. The Scotch Whisky Technical File describes it as similar in aroma and taste to unhopped beer, a useful reminder that fermentation creates an aromatic liquid before distillation begins.[2]

The distinction between wash, new make and mature whisky matters when reading research. A finding about fermentation compounds or new make aroma is not automatically a finding about the finished whisky. The studies discussed here examine different stages and measurements, so their results need to stay attached to those conditions.[1][3][4]

Yeast and its effect on flavour during fermentation

Yeast works within a changing environment. As it ferments, its metabolic activity generates heat; the 2024 review of Scotch malt whisky yeast describes fermentation temperatures rising naturally to about 33°C. That temperature is a reported feature of the process, not a target that every distillery must follow.[1]

The same review reports that fermentation is largely complete after about 30 hours, producing wash at 8% to 10% ABV and bringing its pH down to about 4.2. These figures describe the review’s account of Scotch malt whisky fermentation, rather than a universal timetable for whisky production.[1]

Stage What happens Figures reported in the 2024 review
Yeast addition Yeast is introduced into the sugary wort A common pitching rate is 2 to 4 × 10⁷ cells per ml.[1]
Active fermentation Yeast produces ethanol, carbon dioxide and congeners Temperature rises naturally to about 33°C.[1]
Main fermentation largely complete Much of the alcoholic fermentation has taken place About 30 hours; wash at 8% to 10% ABV and pH about 4.2.[1]

“Pitching” simply means adding yeast. The pitching rate describes how many yeast cells are introduced into a given volume of wort, the sugary liquid being fermented. It is therefore a different variable from yeast strain, even though both can influence the outcome.[1][4]

Nor is a fermentation necessarily finished, in the flavour-making sense, when most alcohol production is complete. The review describes lactic acid bacteria contributing additional congeners during extended fermentation. A longer fermentation should not therefore be understood simply as extra time spent making more alcohol.[1]

What changing the strain can change

The 2024 review identifies yeast strain choice as one of the most important factors in the character of new make and young whisky. Different strains offer different combinations of fermentation performance and congener production, which makes yeast selection a flavour decision as well as a production decision.[1]

Some examples show how specific those differences can be. The review associates Wickerhamomyces anomalus with high levels of ethyl acetate and other acetate esters, linked to fruity and sour notes. It associates Saccharomyces bayanus with compounds including 2-phenylethyl acetate and 2-methylbutanoate, linked to fruity and floral character.[1]

It also discusses yeasts associated with the phenols 4-ethylguaiacol and 4-vinylguaiacol, described as smoky or spicy. These are reported associations between yeasts, compounds and aromas, not tasting notes that can be assigned to every whisky made with those organisms.[1]

A more unusual yeast is not necessarily a better-performing yeast. The review finds that pure cultures of non-Saccharomyces yeasts can have distinctive flavour profiles but often poorer fermentation performance. Poorly performing yeasts can reduce ethanol yield and increase unpleasant notes, including sulphury character.[1]

One approach is a co-culture, using a non-distilling yeast alongside a distilling strain. Some such combinations in the research reduced yield while increasing estery, fruity flavours. The useful question is consequently not just “Does this yeast make more flavour?”, but “Which flavour changes does it produce, and with what effect on fermentation?”[1]

What the 24-strain aroma study found

A 2021 Heriot-Watt study compared 24 commercially available active dried yeast strains and examined the aroma of their new make spirits. Distilling strains could generally be distinguished from brewing and wine strains through aroma and ester levels, supporting the view that yeast selection can leave a recognisable chemical and sensory effect.[3]

Yet the results did not produce a simple league table of strains. The researchers found no statistically significant differences between individual strains in the intensity of seven whisky aroma categories. At the same time, new make produced with yeasts marketed as brewing strains received the preferred acceptability rating.[3]

Those findings answer different questions. Distinguishing broad groups by aroma or ester levels is not the same as demonstrating a significant difference between every individual strain. Likewise, a preference rating in this trial does not establish that brewing yeast always produces preferable whisky.[3]

For a reader, the practical lesson is to treat “distilling yeast” as a description of intended use, not a guarantee of sensory superiority. The 2024 review also reports that bioethanol strains produced spirits with flavours comparable to those from whisky distilling yeast. A yeast’s market category alone does not fully describe its flavour potential.[1]

Why liquid or dried yeast matters

Strain is only part of the choice. A 2023 study involving researchers from Heriot-Watt and Dalhousie universities and The Glenmorangie Company examined yeast format and pitching rate. Liquid yeast had a lag time about 68% shorter than dried yeast and produced more esters under the study’s conditions.[4]

Lag time is the initial delay before fermentation gets under way. The result shows why two accounts naming a yeast strain may still leave out relevant information: the format in which that yeast is supplied can also affect fermentation behaviour and congener production.[4]

Pitching rate mattered too. In fermentations that fully attenuated, meaning that fermentation ran to completion, ethyl ester concentrations generally trended downwards when less yeast was pitched. That finding does not support a simple rule that adding less yeast necessarily creates a fruitier spirit.[4]

The comparison is most useful when its two findings stay separate. Liquid versus dried yeast concerns format; more versus fewer cells concerns pitching rate. Neither should be silently substituted for strain identity when explaining why two fermentations produced different results.[4]

Commercial yeast and experimental choices

Commercial Scotch whisky yeasts named in the 2024 review include MX, Pinnacle and DistillaMax. Yeast is supplied in dried, creamed, caked or stabilised liquid forms. Those choices show that “the yeast” is not a single ingredient specification: strain and physical format are separate details.[1]

Normal fermentations can also contain low levels of other wild yeasts, alongside lactic acid bacteria and, rarely, acetic acid bacteria. Their presence does not mean that a fermentation is primarily driven by wild yeast. The review keeps these background organisms distinct from the selected yeast used for fermentation.[1]

Experimental choices therefore involve balancing several outcomes rather than pursuing novelty alone. The review identifies scope for non-conventional yeasts and co-fermentation strategies, including cases where producers accept reduced ethanol yield in pursuit of a particular flavour result. Distinctiveness and fermentation performance need to be assessed together.[1]

Common mistakes when reading yeast claims

“Yeast only makes alcohol.” This overlooks its production of esters, higher alcohols and other congeners. The misunderstanding comes from treating fermentation solely as the stage that supplies alcohol for distillation, rather than as a stage that also creates flavour.[1]

“Every distillery breeds its own yeast.” A proprietary strain may attract attention, but the review describes Scotch distilleries relying mainly on commercial distilling yeast.[1]

“Sour mash whiskey tastes sour.” The name can be mistaken for a tasting description. The Scotch Whisky Technical File describes sour mash as mash acidified to account for local water conditions.[2]

“More esters means a better whisky.” Ester measurements describe part of the chemical result, not an overall quality verdict. The 24-strain study measured aroma differences and acceptability separately, illustrating why chemical composition and sensory preference should not be treated as interchangeable answers.[3]

“A distinctive strain guarantees a distinctive finished bottle.” The evidence discussed here chiefly concerns fermentation and new make. A strain claim is more informative when accompanied by the study conditions and the stage assessed, rather than presented as a complete explanation of mature whisky’s character.[1][3][4]

Where to go next

Sources

  1. Daute, M., Jack, F. and Walker, G. The potential for Scotch Malt Whisky flavour diversification by yeast. FEMS Yeast Research, volume 24, foae017, 2024. doi:10.1093/femsyr/foae017. https://pmc.ncbi.nlm.nih.gov/articles/PMC11095643/

  2. UK Government, Department for Environment, Food and Rural Affairs. Technical File for Scotch Whisky. June 2019 edition. https://assets.publishing.service.gov.uk/media/5fd36667e90e07662ed92c85/Scotch_Whisky_Technical_File_-_June_2019.pdf

  3. Waymark, C. and Hill, A. E. The influence of yeast strain on whisky new make spirit aroma. Fermentation, volume 7, issue 4, article 311, 2021. Heriot-Watt University research portal abstract. doi:10.3390/fermentation7040311. https://researchportal.hw.ac.uk/en/publications/the-influence-of-yeast-strain-on-whisky-new-make-spirit-aroma/

  4. Reid, S., Speers, A., Lumsden, W., Willoughby, N. and Maskell, D. The influence of yeast format and pitching rate on Scotch malt whisky fermentation kinetics and congeners. Journal of the Institute of Brewing, volume 129, issue 2, 2023. Abstract. doi:10.58430/jib.v129i2.18. https://jib.cibd.org.uk/index.php/jib/article/view/18

This desk-researched article uses the site’s verified fact sheet, drawing on a research review, two study abstracts and the Scotch Whisky Technical File.

Last checked: November 2026