Last updated August 2026

Written by Jesse & Cassie, Wine Scribes — Jesse holds a degree in Viticulture & Enology from UC Davis and has made wine in Burgundy, Yarra Valley, California, Washington and the Douro Valley; Cassie holds WSET Level 2 with Distinction and assists Jesse with work in the vineyard and cellar.

Wine faults are tested twice on the Certified exam: once as theory, and again in the service exam when an examiner asks what you would do about a bottle. Candidates who can name the compound but freeze on the guest interaction lose marks they did not need to lose.

These ten questions cover cork taint and TCA, Brettanomyces, volatile acidity and ethyl acetate, reduction, tartrate crystals, heat damage, lightstrike, mousiness and oxidation — plus the correct professional response when a guest declares a bottle corked. We have named the actual compounds throughout, because being able to say 4-ethylphenol rather than “that barnyard thing” is what separates a confident answer from a hopeful one.

CMS Certified — Old World Regions

Test your Old World wine knowledge for the CMS Certified Sommelier exam. Questions cover Bordeaux, Burgundy, Rhône, Italy, Spain, Portugal, and Germany. Written for self-study purposes only — not affiliated with the Court of Master Sommeliers.

Which compound is chiefly responsible for cork taint? 2,4,6-trichloroanisole (TCA) 4-ethylphenol Acetaldehyde Ethyl acetate

A wine shows barnyard, band-aid and horse-blanket aromas. The most likely cause is: Oxidation Cork taint Brettanomyces Lightstrike

Nail polish remover and a sharp glue-like note most likely indicate: Reduction Excess sulfur dioxide Heat damage Elevated ethyl acetate, the ester commonly found alongside volatile acidity

A wine smells of rotten eggs and struck rubber. The most appropriate first response is: Aerate or decant vigorously, as mild reduction often blows off Return it immediately as irreparably faulted Chill it further to suppress the aroma Add a splash of a different wine to mask it

Tartrate crystals in the bottom of a bottle or on the underside of a cork indicate: Refermentation in bottle Harmless precipitation of potassium bitartrate, not a fault Bacterial spoilage The wine has been diluted with water

Maderisation, or heat damage, typically presents as: Crisp green apple with high acidity Stewed or cooked fruit, flattened aromatics, often with a raised or weeping cork Wet cardboard and muted fruit Barnyard and band-aid

Lightstrike, or goût de lumière, is caused by: Excessive filtration Exposure to UV and visible light, particularly in clear or lightly tinted bottles Storage at excessively low temperature Contact with stainless steel

Which fault is detected only retronasally, after the wine has left the mouth, and builds over the finish? Cork taint Volatile acidity Oxidation Mousiness

A ten-year-old white wine shows deep gold colour, bruised apple and nutty notes, with diminished fruit. This is most consistent with: Reduction Cork taint Oxidation Brettanomyces

A guest declares a bottle corked. Correct professional practice is to: Apologise, remove the bottle without argument, replace it, and log it for supplier credit Taste it yourself and explain why they are mistaken if you disagree Offer a discount on the next bottle Decant it and return it to the table

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How to study wine faults for the Certified exam

Learn each fault by its compound as well as its smell. TCA, 4-ethylphenol, ethyl acetate, acetaldehyde and the tetrahydropyridines behind mousiness all come up, and naming them signals real command of the material.

Know which faults are recoverable. Mild reduction frequently blows off with vigorous decanting, so aerating before condemning a bottle is the correct professional move. TCA never resolves. That distinction is a favourite examiner probe because it separates chemistry from memorisation.

Tartrate crystals are not a fault, and neither is sediment in an old red. Being able to explain both calmly to a guest earns service marks, not theory marks — practise the wording, not just the fact.

Context decides whether oxidation is a flaw: ruinous in a young Sancerre, the entire point in an Oloroso or a Madeira. Keep biological ageing in a separate box, since Fino and Vin Jaune develop under a veil of flor rather than under oxygen. The Wine Service quiz covers the guest-facing side in more depth.

What percentage of wine is affected by cork taint?

Estimates have fallen considerably as closure quality improved, and modern figures are generally cited well below one percent for premium producers. The exam is more interested in whether you can identify it and respond correctly than in the statistic.

Can a corked wine be fixed by decanting?

No. TCA does not dissipate with aeration. Reduction often does, which is why decanting is the right first response to a sulfurous nose but not to a musty one.

What should a sommelier do when a guest says a wine is corked?

Apologise, remove the bottle without argument, replace it, and retain the bottle and cork for supplier credit. Never debate the guest — TCA sensitivity varies enough that they may be detecting something you cannot.

CMS Certified Wine Faults Quiz — 10 Practice Questions

CMS Certified — Old World Regions

How to study wine faults for the Certified exam