May 08, 2023 downloads, knowledge Nicole Irvine

Brewer's Guide to Yeast Flavour & Biotransformation

The following excerpts are from our new e-book, Yeast Flavour & Biotransformation, which is now available for download!

A comprehensive guide to easy, high-impact fermentation, Yeast Flavour and Biotransformation, we want to help you with science, not guesswork, when it comes to honing in on your ideal brew. We'll take you through up-to-date research, aroma compounds, terpene & thiol biotransformation, impacts of temperature and pitch rate, and beer ideas to pull everything you've learned together.

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Yeast Flavour & Biotransformation Research

Why does Escarpment Labs conduct yeast flavour research?

Brewers want to know exactly what flavours they can expect from a new yeast strain. They also want to know what to expect if the operational conditions change in the brewery (such as temperature and pitch rate). We have focused for years on developing the resources to be able to answer these questions properly.

What tools are used?

We use a diverse set of tools in order to help brewers optimize their house yeasts and select new strains. Through our research partnerships, we have access to sophisticated analytical tools that give us a clear picture of the flavour potential in each yeast strain.

For yeast flavour metabolite analysis, we have used various analytical methods including Gas Chromatography Mass Spectroscopy (GC-MS with various sub-methods), High-Performance Liquid Chromatography (HPLC), as well as one of the greatest analytical tools of all: the human nose (a.k.a. sensory analysis). We use analytical and sensory data to help brewers choose a strain and optimize its flavours.

Why does yeast make flavour?

There are still a lot of open questions here! Because we also want to know why yeast makes different flavours, we are committed to combining analytical data with genomic data to understand the genetics underlying our favourite yeast flavour profiles. We have sequenced the whole genomes of all of our public yeast strains.

We are now linking yeast genetics to their flavour output to understand how they work. This will help us develop the next generation of beer yeasts and has already informed the creation of new products such as Saison Maison, Hydra, KRISPY, and Thiol Libre.

Key Yeast Flavours & Fermentation Flavours

Alcohols

Yeast is capable of making a diverse range of alcohols which contribute to its flavour. At low levels, these alcohols can contribute to flavour complexity. For example, 1-octanol is perceived as citrus-like. However, at high levels, fusel alcohols such as isobutanol and isoamyl alcohol can be perceived as “boozy”. Different yeast strains also produce different amounts of glycerol, which contributes to body and mouthfeel in beer.

Esters

Esters are perceived as fruity and floral flavours. There is a wide range of esters that yeast is capable of producing, making this family one of the most interesting to brewers! Broadly speaking, we can divide esters into fatty acid esters such as ethyl hexanoate (pineapple-like) and ethyl octanoate (apple or cognac-like) and acetate esters such as isoamyl acetate (banana-like) and phenylethyl acetate (rose-like).

Phenols

Grain contains phenolic acids, which the grain plant produces as a stress-protectant against fungi in the field. These flavourless phenolic acids can be converted by yeast into volatile phenols such as 4-vinylguaiacol, which gives Belgian beers their distinctive peppery-clove note. In many beers this note is considered an off-flavour, leading to its common term of “POF” (phenolic off-flavour).

Acids

Yeast is capable of making different types of acids, and some yeasts reduce the pH of wort more than others. In typical yeasts, this acid production is minimal and includes succinic acid and acetic acid. Specialized acid producing yeasts (such as Lactic Magic) as well as souring bacteria are capable of producing a wider range of acids, predominantly lactic and acetic acids but also citric acid. These contribute to the tart and refreshing taste of sour beers.

Terpenes

Yeast is capable of both unlocking and transforming terpene compounds (monoterpene alcohols) from hops. This can make a beer taste more citrusy, fruity, or dank. Keep reading to learn more about terpene biotransformation.

Thiols

Certain yeasts are capable of unlocking thiol aromas from flavourless hop and malt precursors. This can make a beer taste more tropical. Keep reading to learn more about thiol biotransformation.