CFPS Beer Faults and Off-Flavors 2 — Questions and Answers
Question 1: What causes 'astringency' — a harsh, drying, puckering sensation — in finished beer?
- Excessive polyphenol/tannin extraction from over-sparging or grain husks at high sparge temperatures (Correct answer)
- Excessive hop rates beyond the style's appropriate IBU range
- High carbonation levels irritating the palate
- Flocculent yeast strains leaving protein haze in the beer
Correct answer: Excessive polyphenol/tannin extraction from over-sparging or grain husks at high sparge temperatures
Polyphenols/tannins leach from grain husks when sparge water is too hot (above 170°F) or wort drops too low in gravity, binding to salivary proteins and causing astringency.
Question 2: Which bacteria species is responsible for producing acetic acid (vinegar) in contaminated beer, especially when oxygen is present?
- Lactobacillus delbrueckii
- Pediococcus damnosus
- Brettanomyces bruxellensis
- Acetobacter aceti (Correct answer)
Correct answer: Acetobacter aceti
Acetobacter oxidizes ethanol to acetic acid in the presence of oxygen, producing a sharp vinegar off-flavor that is a serious contamination fault in most beer styles.
Question 3: What causes the 'Band-Aid,' 'medicinal,' or 'antiseptic' off-flavor occasionally found in beer?
- Excessive use of Chinook hops producing harsh phenolics
- Chlorophenols formed when chlorine (from water or sanitizer) reacts with natural phenolic compounds (Correct answer)
- Yeast autolysis during extended contact with dead yeast cells
- Excessive sulfate in the water profile
Correct answer: Chlorophenols formed when chlorine (from water or sanitizer) reacts with natural phenolic compounds
Chlorophenols form when residual chlorine in water or sanitizers reacts with phenolic compounds from malt/yeast, creating potent medicinal aromas at very low concentrations.
Question 4: What is the primary source of metallic off-flavors in beer, often described as blood, coins, or pennies?
- High CO2 pressure creating carbonic acid in the beer
- Extended dry hopping with high-alpha hop varieties
- Iron, copper, or aluminum contamination from corroded or reactive brewing equipment (Correct answer)
- Lactic acid bacterial infection creating sharp sourness
Correct answer: Iron, copper, or aluminum contamination from corroded or reactive brewing equipment
Iron and copper ions from reactive metals (old equipment, corroded fittings) dissolve into beer, catalyzing oxidation and contributing distinct metallic flavors even at very low concentrations.
Question 5: What is the primary cause of 'gushing' — excessive foaming when a bottle or can is opened?
- Residual fermentable sugars or microbial infection causing continued carbonation beyond intended levels (Correct answer)
- Using finings that react with CO2 to produce extra foam
- High sulfate water profile creating carbonic acid super-saturation
- Aggressive dry hopping that adds carbonation after packaging
Correct answer: Residual fermentable sugars or microbial infection causing continued carbonation beyond intended levels
Gushing occurs when refermentation continues in the package due to residual sugar/yeast or microbial contamination, or from nucleation sites caused by hop compounds (primary gushing).
Question 6: Which compound is responsible for the 'rotten egg' or 'sulfury' aroma sometimes present in lager yeast fermentations?
- Acetaldehyde from incomplete fermentation of sugar to ethanol
- Polyphenol oxidation products from dissolved oxygen
- DMS from inadequate boiling of wort
- Hydrogen sulfide (H2S) produced by stressed or nutrient-deficient yeast (Correct answer)
Correct answer: Hydrogen sulfide (H2S) produced by stressed or nutrient-deficient yeast
Hydrogen sulfide is produced by yeast under stress from nutrient deficiency, high fermentation pressure, or certain lager yeast strains; it normally dissipates with CO2 during active fermentation.
CFPS Beer Faults and Off-Flavors 2
What causes 'astringency' — a harsh, drying, puckering sensation — in finished beer?