The sugars in grape juice that yeast ferments are chiefly
Answer: A
Correct answer: Glucose and fructose
Ripe grapes contain roughly equal amounts of glucose and fructose, together making up most of the must’s soluble solids, and Saccharomyces ferments both. This is why wine needs no mashing stage: the sugar is already present and fermentable, whereas barley must have its starch converted first.
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Compared with wine, beer typically has
Answer: B
Correct answer: Lower alcohol and dissolved carbon dioxide
Beer is typically 4 to 6 per cent alcohol against wine’s 12 to 14, because the wort is less concentrated than grape must, and it retains dissolved carbon dioxide from conditioning while a still wine has had its gas allowed to escape.
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Which would you expect in a brewery but not in a winery?
Answer: C
Correct answer: A mash tun
Only beer needs a mashing stage, because only beer starts from starch that must be enzymatically converted before yeast can act. Grape must arrives with its sugar already fermentable. Cleaning facilities, temperature control and fermentation vessels are common to both.
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The most important general safeguard against spoilage in both a brewery and a winery is
Answer: D
Correct answer: Thorough cleaning and sanitation of all equipment
Spoilage organisms mostly arrive on surfaces, in hoses and in the recesses of fittings, and once established they contaminate every batch that passes. Hygiene therefore prevents the problem rather than treating it, and it is the one measure that guards against Acetobacter, Pediococcus, Brettanomyces and film yeasts alike.
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Which statement about carbon dioxide in these fermentations is correct?
Answer: A
Both beer and sparkling wine keep the gas dissolved under pressure, while still wine is allowed to vent it. The gas comes from yeast fermenting sugar, though lactic acid bacteria produce some in the malolactic step as well.
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A wine described as dry contains
Answer: B
Correct answer: Little residual sugar
A dry wine is one whose fermentation ran to completion, leaving the yeast nothing left to ferment - conventionally under about 4 grams of sugar per litre. Dryness says nothing about the alcohol, which is generally higher in a dry wine precisely because all the sugar was converted.
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The main practical reason for filtering beer before packaging is to
Answer: C
Correct answer: Give clarity and remove remaining yeast
Filtration produces the bright appearance most packaged beers are expected to have and removes the yeast that would otherwise continue to work and settle in the bottle. It is not a substitute for pasteurisation unless the membrane is fine enough to be sterilising, which requires a much tighter filter than clarification alone.
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Which of these is fermented by yeast rather than by bacteria?
Answer: D
Beer is a yeast fermentation producing ethanol, whereas sauerkraut, yoghurt and pickles are all lactic acid bacterial fermentations producing acid. The distinction between yeast and bacterial fermentations runs through the whole of food microbiology.
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Yeast reproduces during fermentation mainly by
Answer: A
Correct answer: Budding
Saccharomyces reproduces asexually by budding: a daughter cell forms as an outgrowth of the mother, receives a nucleus, and separates, leaving a bud scar behind. Binary fission is the bacterial mechanism, and sporulation in yeast is a response to starvation rather than the normal route of growth.
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Which condition would most likely cause an alcoholic fermentation to stop early?
Answer: B
Correct answer: Excessive temperature
A stuck fermentation most often follows overheating, which stresses and eventually kills the yeast - and since fermentation is itself exothermic, a large vessel can run away without cooling. Nitrogen deficiency is the other common cause. Excluding air is normal and desirable once fermentation is under way, and a steady moderate temperature is exactly what is wanted.
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