Yeast and Fermentation

By Dave Hoops

In this edition of Deep Thoughts with Dave Hoops, we look at the most magical part of brewing beer: Yeast and fermentation.


My name is Dave Hoops, Master Brewer at Fitger’s Brewhouse in Duluth, Minnesota. Webster’s defines fermentation as “a change brought about by a ferment, as yeast enzymes, which convert grain sugar into ethyl alcohol.” I say yeast eats sugar and creates alcohol and carbon dioxide. Any way you look at it, brewers are basically yeast farmers. We spend countless hours looking after our yeast, making sure it’s strong and happy, because without yeast no beer can be produced.

Simply put, yeast…

•           Is a single cell fungus

•           Has a similar cell structure to human cells

•           Feeds on sugars, like human cells

•           Is everywhere. Yeast is in the soil and growing on trees, ripe fruit, and many other places.

•           Used in bread, wine, distilled spirits, and cultured in the laboratory are all the same species

Here at Fitger’s Brewhouse we brew both lagers and ales. We also brew both closed and open fermentation batches. Most Growler readers probably know the difference between an ale and a lager. Ales are brewed at warmer temperatures, tend to ferment faster and typically have a fruitier and more character-driven flavor. Lagers are fermented much cooler—twenty degrees or so less than ales—and take around three times longer to ferment. Lagers are then matured another two months in cold conditioning.

Lagers tend to be smoother and more quaffable. They also tend to be the most difficult beers to brew since there are very few esters or flavors other than malt and hop. That means there is no hiding flavors in a mix of heavy hop notes and fruity esters. Even more interesting is the difference in flavor components that can vary between open- and closed-tank fermentations. Closed fermentations are conducted in tanks closed to the atmosphere with a single opening from the tank dedicated to allowing fermentation carbon dioxide to escape. Conversely open tanks have a loose lid over the fermenting wort and are intentionally not airtight.

I have never filtered beer at the Brewhouse because I believe filtering removes flavor, fruity esters or otherwise. I say that with full awareness that if we distributed I would filter because of the flavor stability issues that are inherent in sending beer off-site. Because we control every second of our beer and most of it is sold fresh I do not need to filter.

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