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Beer Science: Yeast – The Life of Beer

As this Buffalo summer flourishes and blossoms, many of you have enjoyed the benefits of many budding beauties. Not trees or flowers, but very small cells known as yeast. Invisible to the naked eye, these fungal friends make alcohol for a living. No, really, these cells would die if they did not carry out the process of fermentation; and alcohol is a byproduct of fermentation. Understanding factors that affect yeast survival and death is therefore an essential obligation of any brewery.

Many different types of yeast accomplish the all-important task of supplying alcohol to beer. All yeast in the world taken together are classified as Fungi. Subsets of yeast can belong to different classification groups called a genus or species. The yeast most commonly used in beer, wine, and bread production is called Saccharomyces cerevisiae. The name Saccharomyces cerevisiae comes from the root “saccharo-” which means sugar (think saccharin, saccharide), and the suffix “-myces” means fungus. The name cerevisiae is derived from Latin and means “of beer” (think “cerveza”, the Spanish word for beer). Although the majority of brewing is done using Saccharomyces cerevisiae, there are cases where other types of yeast are used. One such type of yeast is called Brettanomyces.

Saccharomyces cerevisiae, or beer yeast.

Even though the same species, Saccharomyces cerevisiae, is used in the production of such diverse products as beer, wine, and bread, there are different genetic variants, or strains, used for each purpose.  What makes one strain different from another strain?  That question is a little more complicated to answer, but the short answer is genetics.  Different strains of Saccharomyces cerevisiae have been adapted and tailored for use in breweries, wineries, bakeries, and laboratories over the years to produce or enhance different flavors. Bread yeast have been designed to make great bread and beer yeast have been designed to make great beer.  There are literally thousands of yeast variations, or strains, used to produce different desired byproducts.

Brettanomyces is another type of yeast, also known as “wild yeast”.  Brettanomyces has long been known by brewers and wine-makers alike for the ability to produce interesting and complex flavor profiles.  In fact, some wine makers abhor the word “Brett” because for many wineries Brettanomyces is known as a spoilage yeast.  This yeast has been known to ruin batches of wine and beer.  So what’s different between Brettanomyces and Saccharomyces yeast?

There are numerous differences between these two organisms, but the most relevant when discussing beer production is flavor. The flavors produced by Brettanomyces yeast are very dissimilar from Saccharomyces flavors.  Beer brewed with Brettanomyces may taste overwhelmingly fruity, funky, or be intriguingly perceived as band-aids or barnyard.  Despite the havoc Brettanomyces can cause on winery (and brewery) premises, wine-lovers tend to enjoy these flavors when present in beer because they are reminded of acquainted wine tastes.  Beer-lovers enjoy these flavors because, when managed correctly, these flavors can be strikingly different and delightful from traditional Saccharomyces yeast beer flavors.

Why do Brett yeast result in such a funky beer? As previously mentioned, Brettanomyces yeast can produce very unusual flavors. As with Saccharomyces yeast, Brett yeast use sugars for energy and convert these sugars into alcohol. Brettanomyces yeast will ferment dextrins (long sugar molecules that Saccharomyces can’t break down) and produce different chemicals than Saccharomyces via different metabolic pathways. The predominant chemicals that are produced by Brettanomyces yeast are esters and phenols: esters impart fruit flavors, while phenols are responsible for tastes such as spicy, funky, and smoky. In chemistry, a phenol refers to a chemical that has an “-OH” attached. Two phenols in particular appear responsible for the flavor profiles caused by Brettanomyces yeast: 4-EP and 4-EG.

4-ethylphenol (abbreviated 4-EP): Tastes identified as: band-aids, barnyard, horse stable, antiseptic.


4-ethylguaiacol (abbreviated 4-EG): Tastes identified as: bacon, spice, cloves, smoky.

Interestingly, the ratio of 4-EP to 4-EG was determined to be important in flavor perception.  Beers that possess the same concentration of 4-EP, but different concentrations of 4-EG, may be perceived to taste different.

Brewers may also choose to add Brettanomyces yeast at a certain time point after Saccharomyces yeast has been added.  This can create even more complex flavor profiles, and presumably can help manage the funkiness of the Brettanomyces unique flavors. Brewers may also mix and match yeast as desired to produce a unique flavored beer. Beer produced using Brett can also be aged in barrels for years before tasting, which may add additional wood flavors.

Because Saccharomyces and Brett are living organisms, breweries must maintain strict sanitation protocols. Proper quality control and cleaning measures must be taken in order to insure contamination in brewing equipment is kept to a minimum. Because as grateful as brewers are to their fermentation friends, no brewer wants an issue with infection.


About Buffalo Beer Biochemist

Born and raised in Western New York. Ph.D. in Biochemistry. Professor of Microbiology and Chemistry. And lover of beer.

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