Master Brewer Certification Yeast Biology & Fermentation Science 1 — Questions and Answers
Question 1: What is the scientific name of the yeast species most commonly used in ale brewing?
- Saccharomyces pastorianus
- Saccharomyces cerevisiae (Correct answer)
- Brettanomyces bruxellensis
- Kluyveromyces marxianus
Correct answer: Saccharomyces cerevisiae
Saccharomyces cerevisiae is the top-fermenting yeast responsible for producing ales at warmer temperatures.
Question 2: During which phase of the yeast growth curve does the most vigorous fermentation activity occur?
- Lag phase
- Log (exponential) phase (Correct answer)
- Stationary phase
- Death phase
Correct answer: Log (exponential) phase
The log phase is when yeast cells multiply rapidly and sugar consumption and CO2 production are at their peak.
Question 3: What is the primary byproduct of yeast fermentation alongside ethanol?
- Lactic acid
- Acetic acid
- Carbon dioxide (Correct answer)
- Hydrogen sulfide
Correct answer: Carbon dioxide
Yeast converts sugars into ethanol and carbon dioxide through glycolysis and alcoholic fermentation.
Question 4: What is the typical optimal fermentation temperature range for lager yeast (Saccharomyces pastorianus)?
- 50–55°F (10–13°C) (Correct answer)
- 65–70°F (18–21°C)
- 75–80°F (24–27°C)
- 35–40°F (2–4°C)
Correct answer: 50–55°F (10–13°C)
Lager yeasts are cold-tolerant bottom-fermenters that work best in the 50–55°F range, producing clean flavor profiles.
Question 5: What is the brewing term for the act of adding yeast to cooled wort to begin fermentation?
- Pitching (Correct answer)
- Sparging
- Mashing
- Krausening
Correct answer: Pitching
Pitching refers specifically to the introduction of yeast into wort to initiate the fermentation process.
Question 6: Which yeast property describes how readily yeast cells clump together and settle out of suspension after fermentation?
- Attenuation
- Flocculation (Correct answer)
- Esterification
- Autolysis
Correct answer: Flocculation
Flocculation is the tendency of yeast cells to aggregate and drop out of suspension, affecting beer clarity and yeast harvesting.
Question 7: What does 'apparent attenuation' measure in a fermented beer?
- The alcohol content as measured by gas chromatography
- The percentage of original extract converted to alcohol and CO2, calculated from gravity readings (Correct answer)
- The pH drop during fermentation
- The number of viable yeast cells per milliliter
Correct answer: The percentage of original extract converted to alcohol and CO2, calculated from gravity readings
Apparent attenuation is calculated from the drop in specific gravity and reflects the degree to which yeast has fermented available sugars, though it overstates true attenuation due to alcohol's lower density.
Master Brewer Certification Yeast Biology & Fermentation Science 1
What is the scientific name of the yeast species most commonly used in ale brewing?