Beer Buzz: Yeast Key to Good Beer Making

The Professor held off on the other 3 columns: for any homebrewer knows without yeast there is no beer. Plus yeast could be argued to be THE most important, and the most underrated ingredient. Try a Belgian Abbey Ale vs. an American Pale, for example. Hops can vary in both, and malts. But if you switch the yeasts you may have switched the styles.-The Professor

Written by Andy Ingram for and The Republic

Yeast fermenting wort
There are four basic ingredients in beer. In previous installments of the Beer Buzz I’ve covered three: malt, hops and water.

I’ve held off on the fourth ingredient, yeast, because of the sheer scope of the topic. The amount of information on the science of fermentation is vast and, honestly, it would probably bore anyone with even a passing interest in microbiology.

So let’s take a simpler look at what yeast is and what it does for beer and brewers.

For centuries, before the invention of the microscope, yeast was a largely unknown ingredient in beer. What was known was that during each fermentation a light-colored, creamy substance was produced and was taken from the tops of fermenting beer and added to the next batch.

Some stories go that the substance, which caused the beer to ferment, was simply referred to as, “God is good.”

Of course, with the invention of the microscope, that creamy stuff was classified as yeast.

Yeast is a single-celled microorganism that is responsible for metabolizing sugar and, as a result, producing alcohol, carbon dioxide and various other aromatic and flavor compounds. It is classified as a fungus and has been given the scientific name saccharomyces, from the Greek for “sugar fungus.”

Brewer’s yeast, or saccharomyces cerevisiae, was thought to come in two varieties; top-fermenting ale yeast (s. cerevisiae) and bottom-fermenting lager yeast (s. pastorianus). However, a recent reclassification has listed all beer yeasts as s. cerevisiae, making lager yeast a hybrid of that classification.

See, boring, and a little confusing.

Historically, ale yeast was fermented at warmer temperatures (55-75 degrees, and higher) and would tend to congregate at the tops of fermenters. Lager yeast was fermented cooler (40-50 degrees) and would tend to drop out to the bottoms of fermenters.

But with today’s modern cylindroconical fermenters, most yeast has been “trained” to drop to the bottom. It makes for easier transfers and cleanup without changing the flavor characteristics of the yeast.

So what is the difference? Essentially two things: temperature and diet.

Warmer fermentation temperatures tend to favor faster fermentations, which produce the more fruity, estery aromas and flavors found in ales. Colder temperatures produce smoother, less fruity aromas, and some people say lagers have a drier character because lager yeast can metabolize melibiose, a type of sugar produced from malt, which ale yeast cannot.

Of course, nothing is cut and dried with yeast. You can certainly make a good beer by using ale yeast at cooler temperatures; our Sunbru Kolsch-style ale is a good example. And you can also make fine beer using lager yeast and fermenting it warm; Anchor Steam has been doing it for decades.

The bottom line is that without yeast the other ingredients don’t amount to much, neither do brewers for that matter.

That being said, I would agree: God is good.

Andy Ingram is owner and brewmaster of Tempe’s Four Peaks Brewery. Reach him at Follow him on Twitter (@fourpeaksbrew) or Facebook.

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