Which of the following is a fermented vegetable product?
Answer: A
Correct answer: Sauerkraut
Sauerkraut is cabbage preserved by lactic acid fermentation. Ketchup is acidified with vinegar rather than fermented, and crisps and frozen peas are preserved by removing water and by freezing respectively - three quite different principles of preservation.
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Compared with a fermented pickle, a fresh-pack pickle is
Answer: B
Correct answer: Acidified quickly and usually heat processed
A fresh-pack pickle skips the fermentation entirely: the vegetable goes straight into vinegar with spices and is heat processed in the jar. It is quicker and more uniform, and it lacks the flavour that fermentation develops, which is why both kinds continue to be made.
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The chief hazard of a vegetable fermentation that fails to acidify is that
Answer: C
Correct answer: Spoilage and pathogenic organisms may survive and grow
The acid is the safety barrier, so a fermentation that fails to acidify has no barrier at all - and it is a low-acid, moist, anaerobic mass, which is exactly the condition Clostridium botulinum requires. The consequence is a safety failure rather than merely a disappointing flavour.
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Which pair of conditions best favours the lactic acid bacteria over their competitors?
Answer: D
Correct answer: Moderate salt with the exclusion of air
Salt suppresses most competitors while the lactic acid bacteria tolerate it, and excluding air suppresses the aerobic yeasts and moulds while the lactic acid bacteria do not need oxygen. The two conditions together select for the organisms wanted, which is the whole design of the process.
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Sauerkraut is normally fermented at a temperature of about
Answer: A
Correct answer: Eighteen to twenty two degrees Celsius
The range is chosen for the microbial succession rather than for speed. Too cool and the fermentation drags, giving spoilage organisms time; too warm and later species dominate from the start, giving a harsher product. Around twenty degrees the succession proceeds in order and the flavour develops fully.
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What happens to the sugar content of cabbage during sauerkraut fermentation?
Answer: B
Correct answer: It falls as the bacteria convert it into acid
The sugar is the substrate and the acid is the product, so as one falls the other rises. The fermentation ends when the sugar is exhausted, which is why the final acidity depends on how much sugar the cabbage contained - and why the cultivar and the season affect the result.
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The reason a finished, properly acidified pickle resists spoilage is that
Answer: C
Correct answer: Little sugar remains and the pH is too low for most organisms
Two barriers act together: the acidity prevents growth, and the absence of fermentable sugar leaves nothing to grow on. The organisms are not all destroyed - many survive in a dormant state - and the salt is nowhere near saturation, so those explanations are wrong.
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Which organism is most likely to be responsible if a pickle brine turns ropy?
Answer: D
Leuconostoc converts sucrose into dextran, and it is that polysaccharide which makes the brine pour thickly. Lactobacillus plantarum produces no dextran, Rhodotorula gives pink discolouration, and clostridia belong to late secondary spoilage.
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The gas evolved during the early stage of a sauerkraut fermentation is chiefly
Answer: A
Heterofermentative lactic acid bacteria release carbon dioxide as they ferment sugar, and its evolution is a sign the process has started properly. Hydrogen sulphide and ammonia signal spoilage, and methane has no part in the process.
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Which change indicates that a fermented pickle has begun to spoil after fermentation?
Answer: B
Acid loss with a rising pH is the signature of secondary spoilage, usually because film yeasts or moulds have consumed the lactic acid at the surface. Once the pH climbs, organisms that the acid had been excluding are able to grow.
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