Which term describes wine that has been spoiled by acetic acid bacteria?
Answer: A
Acetic acid bacteria oxidise the ethanol of the wine to acetic acid, which is the acid of vinegar, and the fault is called volatile acidity. Sparkling, fortified and sweet all describe deliberate styles rather than defects.
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Carbon dioxide is released during fermentation because it is
Answer: B
Correct answer: A product of the yeast breaking down sugar
The carbon dioxide is generated by the yeast’s own metabolism, one molecule for each of ethanol as glucose is broken down. It is not dissolved from the air and not derived from the hops - on the contrary, the vigorous evolution of gas is what excludes air from an actively fermenting vessel.
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Which is NOT a stage in the production of beer?
Answer: C
Pressing belongs to winemaking, where juice is separated from skins and pulp. Brewing separates its liquid from the grain by lautering and sparging instead, and the other three stages listed are all central to the process.
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Cool fermentation temperatures are used for white wine and for lager because they
Answer: D
Correct answer: Preserve delicate flavours
In both cases the object is the same: aromatic compounds are volatile, and at higher temperatures they are stripped out with the escaping carbon dioxide or never formed at all. Cool fermentation slows the yeast - a lager may take weeks - but the flavours that survive are the reason for the patience.
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Noble rot, valued in the production of certain sweet wines, is caused by
Answer: A
Under the right dry conditions Botrytis cinerea shrivels the grape and concentrates its sugar and acid, giving the intensity of wines such as Sauternes. In damp conditions the same fungus causes grey rot, which ruins the crop instead.
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Cork taint in wine is caused by
Answer: B
Compounds such as trichloroanisole are detectable at extraordinarily low concentrations and give a musty, damp-cardboard smell that masks the fruit. It is a contamination of the closure rather than a fault of the fermentation.
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A shortage of assimilable nitrogen in grape must may lead to
Answer: C
Yeast needs nitrogen to build cell material, and when it runs short the fermentation slows or halts and the stressed yeast may produce hydrogen sulphide, giving a rotten-egg smell. Winemakers add nutrient salts to avoid both problems.
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Racking a wine means
Answer: D
Correct answer: Drawing the clear wine off its sediment
Racking transfers the clear wine from above the lees into a fresh vessel, leaving the dead yeast and precipitated matter behind. It is done several times during maturation, and it also allows a controlled small exposure to air, which helps the wine develop - though too much invites the acetic acid bacteria.
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Crystals sometimes found in a bottle of wine are usually
Answer: A
Potassium bitartrate becomes less soluble as the wine cools and can crystallise, which is why many wines are chilled before bottling to precipitate it in the cellar instead. The crystals are tasteless and indicate no microbial problem.
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Film-forming yeasts such as Pichia and Candida spoil wine by
Answer: B
Correct answer: Growing as a skin on the surface and oxidising the alcohol
Film yeasts are aerobic and grow at the interface with air, forming a visible white or grey skin on a partly filled vessel. They oxidise ethanol and organic acids, leaving the wine thin and flat. As with Acetobacter, the control is to keep vessels topped up so there is no surface for them to colonise.
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