A well-fermented brined cucumber finishes at a pH of roughly
Answer: A
The accumulated lactic acid, around 1.5 per cent, brings the brine to a pH near 3.1 to 3.5, which is low enough to prevent the growth of spoilage and pathogenic bacteria. A pickle that fails to reach this range is not safely preserved by acid alone.
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Bloater damage in fermented cucumbers is the formation of
Answer: B
Carbon dioxide accumulating faster than it can escape forces cavities inside the cucumber, and the hollowed fruit is unsaleable as a whole pickle. The gas comes chiefly from heterofermentative lactic acid bacteria and from fermentative yeasts.
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Bloater formation in cucumber fermentation is commonly prevented by
Answer: C
Sparging with nitrogen strips dissolved carbon dioxide from the brine before it can build up inside the fruit. Purging with air also works but has to be controlled carefully, since it can encourage mould growth and the softening that follows.
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Lactobacillus plantarum is favoured as a starter for cucumber fermentation partly because it
Answer: D
Malic acid in the cucumber can be decarboxylated to carbon dioxide, and strains that cannot do this generate far less gas, so the risk of bloaters falls. Being homofermentative it also produces little gas from sugar, which helps for the same reason.
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Softening of fermented pickles is caused by
Answer: A
Enzymes that hydrolyse pectin destroy the material cementing plant cells together and the fruit goes limp. They come mostly from moulds, which is why blossoms and trash must be removed and the fruit kept below the brine where moulds cannot grow.
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Adding calcium chloride to a cucumber fermentation brine is intended to
Answer: B
Calcium ions cross-link the pectin of the cell walls and hold the texture, so 20 to 40 millimolar calcium chloride gives firmer pickles, which matters most when the salt concentration is being kept low. It contributes nothing to acidity or nutrition.
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Ropy or slimy brine in a cucumber fermentation is caused by
Answer: C
Leuconostoc converts sucrose into dextran, a long-chain polysaccharide that makes the brine pour like syrup. It is usually a passing stage, since other lactic acid bacteria consume the dextran as fermentation continues.
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A rise in pH with the appearance of butyric and propionic acids late in a cucumber fermentation indicates
Answer: D
Once the lactic acid is consumed the pH climbs and clostridia and other anaerobes can grow, producing butyric and propionic acids and a foul smell. It is a genuine spoilage and not a stage the process is meant to pass through.
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A white film growing on the surface of an open pickle brine is usually
Answer: A
Correct answer: Film yeasts, which oxidise the acid and must be removed
Film or wild yeasts are aerobic and grow at the interface with air, forming a white or grey skin. They consume the lactic acid the fermentation produced, so the pH rises and spoilage organisms are admitted. The film is skimmed off, and better still the brine is kept covered so that no surface is available.
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Sauerkraut and fermented pickles are preserved chiefly by
Answer: B
Acid is the preservative: a pH near 3.5 stops the growth of spoilage and pathogenic bacteria. Salt selects which organisms may grow and helps draw out juice, but at the levels used it does not itself preserve the product, and no heat is applied during fermentation.
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