Tuesday Beer Trivia: Yeast

Put your knowledge of brewer’s yeast to the test in this week’s Tuesday Beer Trivia quiz.

Yeast is the lifeline of beer. Without yeast, there is nothing to transform the sugars in wort into alcohol and carbon dioxide, and ultimately beer! Having an understanding of yeast and what they need for a clean fermentation can make the difference between a good brewer and a great brewer.

After you take the Beer Trivia quiz below, scroll down to “Beer Trivia Answer Explanations” section to learn more about yeast!

Beer Trivia Answer Explanations

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Question 1: Generally speaking, an ale requires 0.75 million viable yeast cells for every milliliter of wort per every degree Plato, while lagers require 1.5 million viable yeast cells for every milliliter of wort per degree Plato. The average package of liquid yeast typically comes with 100 billion viable yeast cells. So, for example, a 5-gallon batch of 1.064 ale wort would require about 227 billion viable yeast cells:

(0.75 million viable yeast cells) x (18925 mL of wort) x (16° Plato) = ~227 billion yeast cells

Question 2: Anton van Leeuwenhoek observed yeast under a microscope in 1680. In 1516, the German Beer Purity law was written, and yeast was left off the list of acceptable ingredients since it was not known. In 1789, Antoine-Laurent Lavoisier described the process of fermentation, but it wasn’t until the mid-1800s that Louis Pasteur established yeast as a living microorganism involved in the fermentation process.

Question 3: Attenuation is the degree of conversion of sugar to alcohol and carbon dioxide. Known yeast strains often come with a percentage of attenuation, which indicates how much of the potential fermentable sugars will be converted during a successful fermentation. Attenuation can be measured by comparing the original gravity with the final gravity, which indicates how much of the sugars were consumed.

Question 4: Both ale (S. cerevisiae) and lager (S. pastorianus) yeasts are of the genus Saccharomyces, meaning “sugar fungus” in Latin. Lager yeast has gone by different names in the past, including S. uvarum and S. carlsbergensisSaccharomyces boulardii is a yeast harvested from lychee fruit and is commonly used as a probiotic.

Question 5: Excerpt from page 229 of Yeast: The Practical Guide to Beer Fermentation: “One of the most common brewer’s yeast mutations is respiratory-deficient mutants, also known as petite mutation. This mutation changes the ability of the yeast to respire. The result is that they grow very small on the aerobic plates (hence the name petite mutants). If the mutations accumulate to more than 1 percent of the yeast population, the result can be poor fermentation performance and flavor problems such as phenolic and diacetyl.”


Sources: 

Homebrewers Association
Homebrewers Association