Every glass of beer holds a number of miracles: the malt, so willing to turn its own starch reserves into fermentables; the perfect bitterness of hops that just happens to be a passable preservative as well; the complex protein chemistry that allows foam to form and remain just so, until the glass is drained. But of all the many wonders of beer, yeast remains by far the most profound.
A millennia ago, the magic maiden Kalevatar, along with her brewing gal-pal Osmotar, of the Finnish-Hungarian national epic, the Kalevala, spend a whole poetic chapter seeking the power needed to kick-start their brew, to get it “…foaming, higher, higher, higher.” They try all the common household products of the day: pine cones, the spit of bears in battle, and more. Having tried everything, a dollop of honey does the job, rendered potent by yeast unwittingly gathered by a honeybee making her rounds.
Ancient people also knew that the waxy sheen on the surface of grapes was brewers yeast and often added grapes or raisins to their brews to initiate fermentation. Yeast, as a vital substance, was well known even as far back as ancient Sumeria, that first great beer brewing civilization that blossomed in Mesopotamia some 5,000 years ago. The nature of yeast, however remained a mystery until researchers in Europe identified it as a single-celled fungus. around 1834.
One species, Saccharomyses cerevesiae, is used by brewers, bakers, vintners and distillers, although the specific strains are different. With the regular surplus of yeast that is an inescapable feature of a brewery, it’s no wonder that a bakery was often located right next door.
Yeast metabolizes sugar and produces alcohol and carbon dioxide gas, which gives beer its foamy prickle. If these were the only two chemicals yeast excreted, beer would be a pretty simple affair. Fortunately for our palates, yeast is kind of a messy eater, and gives off a wide range of flavor chemicals that add spicy, fruity or other appealing aromas to beer.
Think of yeast as little bags of goo. Inside are various structures that synthesize proteins, generate energy and much more. Each cellular process can take a number of steps, which means that there are chemicals floating around in there that are produced by one action and needed for the next. The membrane of the cell is a little leaky—necessary to gain access to ingredients needed for yeasty living—but some of these intermediate products ooze out and remain in the beer. Chief among them are compounds such as esters, phenols and ketones, potent aroma compounds that contribute much of beer’s charming complexity.
All of this chemistry happens faster at higher temperatures, and this creates the great division of beer into ale and lager. Yes, the yeast is slightly different in regard to its tolerance of cool temperatures, but the key difference is that at the cool temperatures of lager fermentation, things happen slowly and the yeast has plenty of time to clean up its messy work environment, leaving lager beer untainted by the fruity and spicy overtones common to ale.
The Yeast Rancher
As a brewer, this is really good stuff to know. Each different strain, especially with ale types, has its own signature set of characteristics, and subtle tweaks of temperature can make dramatic differences in flavor and aroma. Between choice of strain and control of temperature, there is a world of flavor yeast can add to your beer.
Yeast adds an overlay of character that largely follows national origin. English yeast, although widely varied, always has a certain “Englishness” about it, and that is true of other brewing traditions as well. You can take just about any wort and make it taste Belgian just by using Belgian yeast, which is a neat trick if you like Belgian beer. A few styles—saison and hefeweizen for example—are utterly dependant on specific strains for their signature aromas.
Brewers do not make beer. We only make wort, and it’s the yeast that turns it into beer. As a brewer, you must add “yeast rancher” to your list of responsibilities. Yeast likes the same things we do: a nourishing meal, plenty of good company, and now and then a breath of fresh air. For brewers of all (or mostly) malt beers, nutrition is rarely a problem, but it does become an issue in high-adjunct beers and especially in meads, where nutritional supplements are essential. Pitching an adequate amount of yeast is usually covered by following the supplier’s directions, but be advised that with strong beers the amount of yeast needed can rise, often dramatically.
Yeast for homebrewing comes in two forms, dry and liquid. The liquid comes in more varieties, often with known pedigrees. The dry forms are a little more generic, but great strides have been made in dry yeast in the last ten years or so. Either can produce perfectly delicious beer. Read the descriptions carefully; they contain lots of clues as to how each strain might affect your beer.
For advanced brewers, yeast culturing is well within the capability of reasonably advanced brewers, although far too complicated to describe here. It pretty much follows basic microbiological techniques. With a bit of kit and some basic skills, you can preserve yeast, grow it up from bottled commercial beer, and join the secret society of yeast rustlers and rare strain traders.
Below is a recipe designed to be adaptable to a number of different yeast types. With an English strain it becomes a summer, or golden bitter. With a Kölsch yeast, you have a fair version of that style. Use a Bavarian weizen yeast, and it will morph into a reasonable approximation of that style, and with the various Belgian strains, you can ferment up a brew with many possible personalities. And who doesn’t like a blonde with a little mystery about her?
A brewer since 1984, Randy Mosher is a nationally recognized writer and authority on brewing and beer styles. He is the author of The Brewer’s Companion (Alephenalia Publications, 1984), Radical Brewing (Brewers Publications, 2004) and Tasting Beer: An Insider’s Guide to the World’s Best Drink (Storey, March 2009). In addition, Mosher consults on package design and branding.