Beer Yeast Part II

Yeast makes beer. That statement requires some clarification; yeast fermentation turns pre-fermented sugar-water called wort into beer, this is the basis for what was discussed last time. Yet there is no universal strain of yeast, and there are many different types that, depending on how fermentation occurs, impact flavour and body.

The oldest and most common type of yeast is domesticated brewer’s yeast, known to exist since before human civilizations developed systems of writing. Scientifically, it is called Saccharomyces cerevisiae, and often generally as ale yeast. The majority of beers made in the craft, commercial, or homebrew settings are made using a form of this yeast.

There are so many different types of ales, with strains like London Ale, New England Ale, Irish Ale, German Wheat, American Wheat, American Ale, Belgian Ale; one could spend hours listing them all. Such a list would be further redundant as many of those strains can be further subdivided into additional categories. Like a list of dog breeds, all these ale yeasts are the exact same species, yet selective pressures during growth/development create great variation in each strain leading to more unique characteristics over time. The location for cultivating multiple generations is the biggest factor that creates that differentiation (notice how many strains listed earlier were tied to a country). Even the Norwegian Kveik yeast that is used in our farmhouse saison, is the same species! Yet a beer made with it will taste very different to more-subdued ale strains.

Factors used to describe and differentiate yeasts include:

·         attenuation, the percentage of total consumable sugars that yeast cells are likely to consume under healthy fermentation

·         flocculation, how easily yeast clumps together after food is eaten and the cells enter dormant state (for more on the life cycle of yeast in fermentation, see that previous yeast blog entry

·         optimal temperature, the range in which fermentation occurs most effectively

·         and most variedly: the flavour profile, which is often determined by which biochemical compounds are formed as by-products of fermentation (more on that another time)

Yeast after the bulk of fermentation is complete, and has become dormant. Over time, colonies of yeast cells may begin to take on new characteristics, producing new flavour components.

For those less familiar with specific ale strains, you may wonder how lagers beers fit into all of this or perhaps you know that lagers are technically different from ales but not the technicalities.  Lagers tend to be greatly different from ales in terms of general factors, this radical shift due to lager strains being a different species, though still genetic cousins to ales. The scientific name is Saccharomyces pastorianus. Fun fact: the lager yeast is named after famous French Chemist Louis Pasteur, known for pioneering the pasteurization process, and the previous name of lager yeast was known as S. carlsbergensis after the Carlsberg brewery where it was formally discovered.

Another difference you may have been told is that lager yeast is ‘bottom-fermenting’ while ale yeast is ‘top-fermenting’. Once this was a common belief about the physiological traits of brewer’s yeast, this is now seen as redundant and outdated. During fermentation, yeast cells spread out evenly across all surfaces in solution. Cell metabolism and fermentation are not confined in one area of a tank.

Common Name OriginOld English ‘alu’ and old Norse ǫl’, ale originally meant any unhopped malt liquor, while beer was restricted to hop-added brewsFrom German ‘lagern’ meaning to store, as the style fermented best in cold, storage areas where beers were kept for longer periods to time 
Scientific NameSaccharomyces cerevisiaeSaccharomyces pastorianus
Fermentation Range17-25 Celsius (not limited to this range, can go lower or much higher)11-16 Celsius (not limited to this range, can go much higher)
Yeast CharacteristicsFaster fermentation, which more variety in volatile and flavourful compoundsSlower, colder fermentation with less varying flavour profiles and cleaner, crisper mouthfeel in brands
Types of Beers Typically ProducedPale Ales, IPAs, Stouts, Porters, Bitters, Wheat beers, etc.Lagers, Pilsners, Bocks, Schwarzbier, Amber lagers, etc.
The differences between ale and lager strains: a primer

The large amount of variation in all these yeast strains making large amounts of beer styles, tells us that genetic variation is very possible over time. Brewers have been doing this, sometimes unintentionally, over many generations. We’ll go over what can cause these variations, and how yeast strains evolve, next time. 

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