Master Brewer Certification Brewer Quality Control & Testing 3 — Questions and Answers
Question 1: Which dissolved gas measurement is most critical to monitor immediately before beer packaging to prevent staling?
- Dissolved oxygen (DO) (Correct answer)
- Dissolved carbon dioxide
- Dissolved nitrogen
- Dissolved sulfur dioxide
Correct answer: Dissolved oxygen (DO)
Dissolved oxygen measured in ppb (parts per billion) before packaging is critical because oxygen uptake at this stage causes oxidative staling, the leading cause of off-flavor development.
Question 2: What is the acceptable range for pH in a typical American lager wort before pitching yeast?
- 5.2–5.4 (Correct answer)
- 4.0–4.2
- 6.0–6.5
- 5.8–6.2
Correct answer: 5.2–5.4
A mash and wort pH of 5.2–5.4 optimizes enzyme activity during mashing and supports healthy yeast metabolism and hop utilization.
Question 3: A QC technician detects elevated levels of acetaldehyde in packaged beer. What does this most likely indicate?
- Premature packaging before yeast completed fermentation (Correct answer)
- Excessive dry hopping contact time
- High sulfate content in brewing water
- Over-carbonation during conditioning
Correct answer: Premature packaging before yeast completed fermentation
Acetaldehyde, which smells like green apples, is a fermentation intermediate normally reabsorbed by yeast — elevated levels indicate yeast were removed before conditioning was complete.
Question 4: What analytical instrument is commonly used for routine measurement of ethanol content in finished beer?
- Anton Paar density meter or distillation-based ebulliometer (Correct answer)
- Refractometer
- UV-Vis spectrophotometer
- Gas chromatograph exclusively
Correct answer: Anton Paar density meter or distillation-based ebulliometer
Anton Paar oscillating U-tube density meters provide rapid, accurate ABV calculation, while ebulliometers use boiling point differential — both are common brewery QC tools.
Question 5: During sensory evaluation of a beer, a panel identifies a 'cooked corn' or 'creamed corn' off-flavor. Which compound is responsible?
- Dimethyl sulfide (DMS) (Correct answer)
- Diacetyl
- Isoamyl acetate
- Acrolein
Correct answer: Dimethyl sulfide (DMS)
DMS (dimethyl sulfide) produces a cooked corn or vegetable aroma in beer, typically from inadequate wort boiling or slow chilling that allows S-methyl methionine (SMM) to convert.
Question 6: What is the primary purpose of an EBC (European Brewery Convention) color measurement in beer QC?
- Quantifying beer color in standardized units using a spectrophotometer at 430nm (Correct answer)
- Measuring turbidity caused by yeast suspension
- Determining total polyphenol content
- Assessing oxidation level of the finished product
Correct answer: Quantifying beer color in standardized units using a spectrophotometer at 430nm
EBC color is measured by absorbance at 430nm in a 1cm cell and multiplied by a factor, providing a standardized numerical color value comparable across breweries.
Question 7: What is the VDK (vicinal diketone) rest used for during lager fermentation?
- Warming beer to help yeast reabsorb diacetyl and 2,3-pentanedione (Correct answer)
- Reducing sulfur compounds through controlled oxidation
- Precipitating protein-polyphenol complexes before filtration
- Adjusting carbonation levels to target specification
Correct answer: Warming beer to help yeast reabsorb diacetyl and 2,3-pentanedione
A VDK rest at 60–65°F activates yeast enzyme activity to reabsorb diacetyl and 2,3-pentanedione (vicinal diketones) that cause buttery off-flavors.
Master Brewer Certification Brewer Quality Control & Testing 3
Which dissolved gas measurement is most critical to monitor immediately before beer packaging to prevent staling?