Beer Styles: Yeast at work construction ahead - part 8

A bucket of yeast and beer gases off as fermentation
carbon dioxide is passed through bucket.  Visible only
with powerful microscopes single cell yeast convert
malt, hops and water into beer.  In olden times yeast
was simply called "Godisgood."  Photo by Charlie
Papazian

There are 50,000,000 yeast cells in one milliliter of beer during fermentation.  Each single cell microorganism metabolizes fermentable carbohydrates and emits gas, alcohol and the taste of beer one infinitesimal act at a time. 

Most beer is made from one of two different yeast types.  Lager yeast (s. uvarum) or ale yeast (s. cerevisiae) . There are hundreds of strains of these two types of yeast.  When used in a traditional manner a particular strain of yeasts will behave somewhat predictably, producing distinctive characters in beer.  Particular strains of yeast have been catalogued and can be chosen to produce desired levels of estery/fruity character, alcohol types, sulfur compounds, diacetyl compounds (butterscotch or butter-like flavor and aroma character) and phenolic compounds (often described as clove-like and smoky).  Yeast strains are also chosen to minimize undesirable characters.  Of note is the fact that one brewers undesirable character is another brewers desired character; and vice versa.

All ale yeasts are not the same.  For example one brewer may wish to accent the fruitiness of English-style ales.  Another brewer may wish to brew strong ales with Belgian-style fruitiness.  Two very different strains of ale yeast are used for these two styles.  Brewers have found that some strains of yeast are particularly suited to replicating the character of certain style of ale and lager.  

Photo left: Micron size yeast cells show bud scars from which offspring have separated. Photo courtesy of Adolph Coors Company.

Furthermore, some brewers may be brewing 5 barrel batches while others ferment 100 or even 1,000 barrels at a time. 

The volume of liquid has an immense effect on the behavior and health of yeast.  The pressure upon the yeast cell wall at the bottom of 100 barrel tank is dramatically greater than at the bottom of a homebrewer’s 5 gallon carboy.  Varieties of yeast under these conditions will perform differently.  One may not sediment well after fermentation is finished or may produce undesirable flavors and aroma due to the stress of pressure on the cell walls of the yeast.  Another yeast may be effected by the osmotic pressure of too much sugar in solution (strong beers) and is not as capable of completing fermentation as effectively as another yeast. 

Yeast varieties are capable of adapting to their environment and produce “house” character to a beer that is desired by the local beer drinker.  Yeast is a living organism effected by many of the same stress factors as the human body; time, temperature, pressure, motion, nutrition, etc.

Lager yeasts are just as temperamental.  To maximize a certain character brewers may choose strains that are capable of fermenting high strength beer, sediments cleanly, producing few off or fruity characters at high temperatures or are capable of resisting mutation over multiple generations of use.   Lager yeast, unlike ale yeast are capable of metabolic activity/fermentation at temperatures close to freezing.  For most strains of ale yeast the lower limit for dependable fermentation is about 60 degrees F.

Photo above right: Blurp! One cell at a time they are invisible. Together yeasts are blurping their way to beer.  Photo Charlie Papazian

Brewers are not simply content with lager and ale strains of yeast.  The Lambic traditions of Belgium and exotic fermentations of other beer cultures have inspired the use of wild strains of yeast often harvested from the ambient air.  Wild yeasts can also be cultured, though that seems to be oxymoronic, but effective.  Brettanomyces strains are some of the most common wild yeasts today’s brewers use for some of their specialty beers.  These strains evolve beer character over many months of aging, sometimes years. 

Bacteria is not yeast, but it’s a microorganism which brewers can introduce under controlled situations to enhance certain characters.  The most common bacterial strain used by brewers is lactobacillus.  It’s the same type of bacteria that turns milk in to yogurt, cucumbers into traditional crock pot pickles and cabbage into sauerkraut.  When skillfully introduced into beer it can promote a refreshing tartness or accent fruit additions.

Can a brewer make an ale with lager yeast?  Can they make a lager with an ale yeast?  Technically and traditionally no.  But when all that matters is the perception of what the beer drinker experiences the debate begins.  Beers tasting like certain styles of lager beers can be made with ale strains of yeast and beers tasting like certain styles of ales can be made with lager strains of yeast. 

The possibilities are limitless.

Next: Beer Styles: Beer brewing process variables influence style - part 9 
 

Guide to entire 27-part Beer Style Series - table of contents