A Guide To Yeast

A Guide To Yeast

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Even though you can’t see them yeast are on of the most important parts of beer. Yeast is what takes sugar and turns it into alcohol and CO2. Without yeast, there would be no alcohol as we know it. This being said, all yeast is not created equal. Besides the fact that there are yeast strains meant specifically for both bread and beer, the specific yeast strain you use for a beer can completely change how it tastes and how it is fermented. We mentioned yeast in our Home Brewing 101 post, but let’s go deeper into this topic.


Let’s take a look at what exactly yeast is and what it means to beer.



What Are Yeast?



Techincally, yeast are single celled microorganisms that reproduce using a system called “budding.” Yeast are classified as a type of fungi, and convert carbohydrates (in the case of beer, sugar) into alcohol, as well as some other byproducts. Talking specifically about brewing yeast, we put them into two categories, even though they are all the same basic strain. These are Ale Yeast (top fermenting), and Lager Yeast (bottom fermenting). Check out this Wikipedia post on yeast and beer for some more details.


Let’s look at these two different types of brewing yeasts.



Top Fermenting Yeast

Ale yeast strains are best used at temperatures from 50 to 77°F, though some strains will not actively ferment below 53°F. Ale yeasts are regarded as top-fermenting yeasts since they rise to the surface during fermentation, creating a very thick, rich yeast head. That is why the term “top-fermenting” is associated with ale yeasts. Fermentation by ale yeasts at these warmer temperatures produces a beer that is high in esters, which many regard as a distinctive character of ale beers.


Top-fermenting yeasts are used for brewing ales, porters, stouts, Kölsch, as well as wheat beers. For our first home-brew project, we will be using top-fermenting yeast.



Bottom-Fermenting Yeast

Lager yeast strains are best used at temperatures ranging from 45 to 60°F. At these lower temperatures, lager yeasts grow less rapidly than ale yeasts, and with less surface foam they tend to settle out to the bottom of the fermenter as fermentation finishes. This is why they are referred to as “bottom” yeasts. The final flavor of the beer will depend a great deal on the strain of lager yeast and the temperatures at which it was fermented. This is why storing this type of beer in the cold for fermentation is called “lagering” the beer.


Some of the lager styles made from bottom-fermenting yeasts are Pilsners, Dortmunders, Märzen, and Bocks.



Other types of Yeast:


Spontaneous Fermentation

Beer that is exposed to the surrounding open air to allow natural/wild yeast and bacteria to literally infect the beer, are spontaneous fermented beers. One of the typical yeasts is the Brettanomyces Lambicus strain(sometimes called “Brett”). Beers produced in this way are sour, generally non-filtered, and are inspired by traditional lambics. This brewing method has been practised for decades in the West Flanders region of Belgium.



What’s Left When Fermentation Stops?


Yeast Byproducts

Yeast impact the flavor and smell of beer more than you know. The flavor and smell of beer is very complex, being derived from an array of components that come from a number of sources. Not only do malt, hops, and water have an impact on flavor, so does the yeast, which forms byproducts during fermentation. The most notable of these are, of course, ethanol (alcohol) and carbon dioxide (CO2); but in addition, a large number of other flavor compounds are produced such as:

  • medicinal (chemical or phenolic character)
  • sulfur (reminiscent of rotten eggs or burnt matches)
  • solvent (reminiscent of acetone or lacquer thinner)
  • fruity / estery (flavor and smell of bananas, strawberries, apples, or other fruit)
  • clove (spicy character reminiscent of cloves)
  • dimethyl sulfide (DMS) (taste or smell of sweet corn, cooked veggies)
  • phenolic (flavor and smell of medicine, plastic, Band-Aids, smoke, or cloves)
  • diacetyl (taste or smell of buttery, butterscotch)
  • acetaldehyde (green apple smell)

There are other yeast byproducts, and some of the listed can be both desired byproducts and/or undesired depending on the beer style or what the brewer was trying to achieve.



Wrapping up

This is a lot of information to take in, but as long as you understand the importance of yeast, the rest will come. This is why it’s a great idea to closely follow a recipe whens tarting to brew, as the yeast type is chosen for you already.


Overall, yeast is far more important than you can imagine in how your beer smells and tastes. It does far more than just give you alcohol. Used correctly, yeast will not only make your wort have the alcohol you are looking for, but will help to impart the smell and taste you want as well.





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