CFPS Off-Flavors and Quality Control 2

Question 1

What is oxidation in beer and what flavor does it typically produce?

Accepted Answer

Reaction of beer compounds with oxygen producing stale cardboard, sherry-like, or papery flavors, particularly in hop-forward beers

Answer

Oxygen reacts with melanoidins, alcohols, and other beer compounds (especially trans-2-nonenal) to produce stale flavors ranging from cardboard/papery to sherry-like depending on the degree and timing of exposure.

Question 2

A 'catty' or 'black currant' aroma in beer is most commonly caused by:

Accepted Answer

4-mercapto-4-methylpentan-2-one (4MMP), a thiol from certain hop varieties or oxidative stress

Answer

4MMP is a potent thiol compound naturally present in some hop varieties (e.g., Nelson Sauvin) or formed through oxidative degradation, detectable at extremely low concentrations with a cat urine or black currant character.

Question 3

Polyphenol (tannin) astringency in beer is best described as:

Accepted Answer

A drying, puckering, gripping sensation in the mouth caused by polyphenols binding to salivary proteins

Answer

Tannins and polyphenols from grain husks or hops precipitate salivary proteins, reducing lubrication and causing the characteristic drying, gripping mouthfeel associated with over-sparging or overboiling.

Question 4

What causes 'gushing' in a bottled beer when it is opened?

Accepted Answer

Overcarbonation from residual fermentable sugars, infection with wild yeast/bacteria, or fungal-derived proteins acting as nucleation sites

Answer

Gushing occurs when excess CO2 comes out of solution rapidly due to overcarbonation, nucleation sites from infection, or hydrophobic proteins from Fusarium malt fungi that trigger foam formation.

Question 5

The off-flavor 'isoamyl acetate' at high levels smells like:

Accepted Answer

Banana candy or nail polish remover

Answer

Isoamyl acetate is a fruity ester naturally produced by ale yeasts; at appropriate levels it contributes pleasant banana notes (desired in Hefeweizen), but excessive amounts smell like artificial banana candy or solvent.

CFPS - Certified Cicerone Practice Test

CFPS - Certified Cicerone Practice Test

CFPS Off-Flavors and Quality Control 2