The main reason a vegetable fermentation is not sterilised before it begins is that
Answer: A
The organisms that do the work arrive on the vegetable itself, so destroying them would leave nothing to ferment the sugar. Where a starter culture is used the raw material may be treated, but the classical process depends on the natural flora.
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Compared with heat sterilisation, preservation by lactic fermentation
Answer: B
Because no heat is applied, texture, colour and heat-sensitive vitamins survive better than in a canned product. The food is not sterile, though: it holds a large live population of lactic acid bacteria, held stable by the low pH.
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Which would be the best single indicator that a sauerkraut fermentation is proceeding normally?
Answer: C
Falling pH shows the lactic acid bacteria are converting sugar to acid, and the early gas is the signature of the heterofermentative Leuconostoc stage. A pH that climbs, or that never moves, means the fermentation has failed or has been overtaken.
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The acid that gives sauerkraut its sour taste is
Answer: D
Lactic acid is the main product of the bacteria that carry out the fermentation, and it accounts for both the sourness and the preservation. Small amounts of acetic acid contribute to flavour, but the mineral acids listed play no part in any food fermentation.
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The salt used in vegetable fermentations is
Answer: A
Common salt, sodium chloride, is what draws out juice and selects for the lactic acid bacteria. Calcium chloride is sometimes added as well to keep the fruit firm, but the bulk of the salt in any of these processes is sodium chloride.
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Brine in a pickle tank is
Answer: B
Correct answer: A solution of salt in water
Brine is simply salt dissolved in water, and its strength governs the whole fermentation: enough to suppress most spoilage organisms and to draw juice from the vegetable, but not so much as to inhibit the lactic acid bacteria themselves. The concentration is the principal control the maker has.
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Rhodotorula, responsible for pink kraut, is a
Answer: C
Rhodotorula is a pigmented yeast, and it is those carotenoid pigments that discolour the kraut. Knowing it is a yeast explains the control measure: correct, evenly distributed salt lets the lactic acid bacteria outgrow it.
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Leuconostoc mesenteroides is classified as a
Answer: D
Leuconostoc is a lactic acid bacterium, Gram-positive and non-sporing, and it is the first organism of the kraut succession. It is easy to confuse with yeasts because it produces gas, but gas production is not confined to yeasts.
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Moulds are unable to grow beneath the brine in a pickle tank because they
Answer: A
Moulds are strict aerobes, so submersion denies them the oxygen they need, and that is precisely why the fruit is kept weighted down. Many moulds tolerate salt and acid quite well, so neither of those alone would stop them.
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A vegetable fermentation is described as spontaneous when it
Answer: B
A spontaneous or natural fermentation depends on the microflora carried in on the raw material and the equipment, with salt and anaerobiosis steering which of them prevail. A controlled fermentation adds a chosen starter culture instead.
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