Beer Faults and Off-Flavors Flashcards
6 cards from real CFPS practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 6 Beer Faults and Off-Flavors flashcards as text
What specific compounds produced by Brettanomyces yeast create the phenolic 'barnyard' and 'leather' aromas in affected beer?
Answer: 4-ethylphenol (4EP) and 4-ethylguaiacol (4EG) from Brett metabolism of phenolic precursors
Brett decarboxylates ferulic and p-coumaric acids from grain into vinyl phenols, then reduces them to 4-ethylphenol (barnyard) and 4-ethylguaiacol (smoked spice).
What brewing procedure is used to reduce residual diacetyl before packaging lager beer?
Answer: A diacetyl rest — raising fermentation temperature to 65-68°F for 24-48 hours before cold conditioning
Warming the beer to near ale temperatures (65-68°F) for a diacetyl rest reactivates yeast metabolism, allowing them to reabsorb and reduce the remaining diacetyl before cold lagering.
What is 'hop creep' and what problem does it cause in heavily dry-hopped beers?
Answer: Enzymes from dry hops (amyloglucosidase) break down previously unfermentable dextrins, restarting fermentation and causing over-carbonation
Hops contain active amyloglucosidase enzyme that can break down limit dextrins into fermentable sugars, causing unexpected refermentation and dangerous over-carbonation in packaged beer.
What off-flavor results from yeast autolysis — the breakdown of yeast cells during prolonged contact with settled yeast?
Answer: Meaty, brothy, rubbery, or soy sauce-like flavors from intracellular yeast contents
When yeast cells die and rupture, they release intracellular contents including proteases and fatty acids that create savory, meaty, or rubbery off-flavors.
Which volatile sulfur compound produces 'catty,' 'black currant,' or 'ribes' off-flavors, sometimes found in sunstruck or improperly stored beer?
Answer: 4-mercapto-4-methylpentan-2-one (4MMP), a thiol released by UV degradation of hop compounds
4MMP is a potent thiol with a black currant or catty character; it can be produced from certain hop varieties or formed during lightstruck reactions in exposed hop compounds.
Which observable change in beer appearance is a reliable indicator that oxidation has occurred during aging?
Answer: Beer darkens or takes on a reddish-brown tinge from melanoidin oxidation
Oxidation causes Maillard-derived melanoidin compounds to polymerize and darken, resulting in a visibly deeper, browner color in aged or stale beer.