Yeast used for fermentation is best described as
Answer: C
Yeasts are unicellular fungi, which is why they are affected by antifungal rather than antibacterial measures and why they are so much larger than the bacteria that spoil these products. Moulds are also fungi but grow as filaments.
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The main reason yeast produces ethanol rather than carbon dioxide alone is that
Answer: D
With oxygen the yeast can respire the sugar completely to carbon dioxide and water, but without it the pathway stops at ethanol, which is excreted as waste. Excluding air is therefore what makes an alcoholic fermentation alcoholic.
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The alcohol present in wine and beer is
Answer: A
Ethanol is the alcohol produced in quantity by yeast fermentation and the one responsible for the strength of both drinks. Small amounts of other alcohols occur and contribute to aroma, but none of them is the principal product.
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Which raw material is fermented to make wine?
Answer: B
Wine is made from grapes, whose juice already contains the sugar the yeast needs. Malted barley gives beer, salted cabbage gives sauerkraut and milk gives fermented dairy products, each with its own microbial community.
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Hops are added to beer chiefly for
Answer: C
Correct answer: Bitterness
The alpha acids of the hop cone isomerise during the boil into iso-alpha acids, which are intensely bitter and balance the sweetness of the malt. Hops also contribute aroma and have a useful antibacterial effect against lactic acid bacteria, but they supply neither enzymes nor sugar nor yeast.
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Fermentation of both wine and beer is conducted with air
Answer: D
Yeast only produces ethanol in quantity when oxygen is absent, and admitting air both diverts the yeast towards respiration and invites acetic acid bacteria and moulds. A small amount of oxygen at pitching is the one exception, as it helps the yeast multiply.
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Which of these is a fermented alcoholic beverage?
Answer: A
Beer is produced by yeast fermenting the sugars of malted grain to ethanol. Vinegar is made by oxidising an alcoholic liquid and so contains little or no alcohol, while juice and pasteurised milk are not fermented at all.
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Pasteurisation of beer is intended to
Answer: B
A brief heat treatment kills the organisms that survive into the package, so the beer keeps without refrigeration. It is applied after fermentation is complete and changes neither the strength nor the bitterness appreciably.
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Which stage comes first in brewing?
Answer: C
Correct answer: Malting
The sequence is malting, milling, mashing, lautering, boiling with hops, cooling, pitching, fermentation, conditioning or lagering, and packaging. Malting comes first because it happens to the barley before it ever reaches the brewery, and is often carried out by a separate maltster.
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Yeast is added to cooled wort in a step known as
Answer: D
Correct answer: Pitching
Pitching is the addition of yeast to cooled wort, and the pitching rate - the number of viable cells per volume - is one of the brewer’s important controls. Kilning, lautering and sparging all belong to earlier stages, before the yeast is involved at all.
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