CFPS Off-Flavors and Quality Control

Question 1

What aroma is associated with acetaldehyde in beer, and what causes it?

Accepted Answer

Green apple or fresh-cut grass, caused by incomplete fermentation when yeast haven't fully reduced it to ethanol

Answer

Buttery butterscotch from bacterial contamination

Answer

Vinegar sharpness from acetic acid production

Answer

Rotten egg smell from hydrogen sulfide

Question 2

The compound responsible for a 'skunky' or 'lightstruck' aroma in beer is:

Accepted Answer

3-methylbut-2-ene-1-thiol (MBT)

Answer

Diacetyl

Answer

Dimethyl sulfide (DMS)

Answer

Isoamyl acetate

Question 3

What off-flavor is described as 'cooked vegetables, creamed corn, or cabbage' and is caused by dimethyl sulfide (DMS)?

Accepted Answer

A cooked or vegetal character from DMS, which forms from S-methylmethionine (SMM) during wort production

Answer

A roasty, acrid character from over-kilned malt

Answer

A cheesy, goaty character from isovaleric acid

Answer

A medicinal plastic character from chlorophenols

Question 4

Acetic acid off-flavor in beer smells and tastes like:

Accepted Answer

Vinegar or nail polish remover

Answer

Rotten eggs

Answer

Buttered popcorn

Answer

Band-Aid or medicinal

Question 5

What is the cause of a 'Band-Aid' or 'medicinal' off-flavor in beer?

Accepted Answer

Chlorophenols formed by wild yeast (especially Brettanomyces) or the reaction of chlorine sanitizers with phenolic compounds

Answer

Excessive lactic acid from LAB contamination

Answer

High levels of carbonation creating an astringent texture

Answer

Autolysis of dead yeast releasing sulfur compounds

Question 6

Which sensory threshold concept explains why a trained taster can detect an off-flavor that most drinkers miss?

Accepted Answer

Flavor threshold — trained tasters develop lower detection thresholds and can identify off-flavors at sub-threshold levels for average consumers

Answer

Flavor fatigue — constant exposure to off-flavors makes the average drinker immune

Answer

Retronasal olfaction — trained tasters use a different sensory pathway

Answer

Capsaicin suppression — spicy food masks off-flavor detection