26.3 Fermented vegetables

Three words: fermented, acidified, pickled

Vegetables can be kept with acid in two ways, and the words for them differ.

• A fermented vegetable is soured by microbes that make acid. Extra acid may or may not be added too.
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• An acidified vegetable is soured by adding acid directly.
• Pickle covers either kind, though it most often means vegetables kept in acetic acid.
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Cucumbers, cabbage and olives are the fermented vegetables sold most widely, but many others are made. Choosing and preparing the vegetables themselves is covered with vegetables. see chapter 17: Buying, storing and preparing vegetables

Why cabbage turns more sour than cucumber

Fresh cabbage holds about 4–8% sugars that microbes can ferment: glucose, fructose and sucrose. Cucumbers hold far less. More sugar means more acid, so a cabbage ferment ends at a much lower pH (more acid) than a cucumber pickle, and sauerkraut tastes sourer.

Vegetables also carry tough carbohydrates that microbes cannot easily use, known together as fiber. Two are cellulose, long chains of glucose, and pectin, the material that holds plant cells together.

Salting and packing

Yeasts and many other microbes already live on the skin of raw vegetables, so nothing needs to be added to start a ferment.

• Shred the cabbage, or prepare another suitable vegetable, and pack it into a jar.
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• Add salt, either dry or as a brine (salt dissolved in water), so that the vegetable ends up completely covered by liquid.
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• Press down firmly. Pressure squeezes juice out of the cabbage, and that juice carries the sugars and nutrients the bacteria need.

The salt does three jobs:

• It holds back many of the organisms that would spoil the food.
• It breaks open the plant cells so their sugars flow out for the bacteria.
• It seasons the pickle.

Salt may also stop enzymes that break down pectin and cellulose, which helps a pickle stay firm.

Two stages of bacteria

A vegetable ferment is called wild, because it relies on the lactic acid bacteria already on the vegetable rather than on an added culture. At first many kinds of bacteria compete. As the lactic acid bacteria release acid, the pH falls and most of the others die. Some producers put acetic acid into the brine right at the beginning.

• First stage. Leuconostoc bacteria, which need no oxygen, ferment the sugars. This is a heterolactic fermentation, so it makes more than lactic acid. The vegetables must stay under the brine and away from air for the first week.
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• Second stage. The acid grows too strong for Leuconostoc, and it dies out. Lactobacillus, which copes better with acid, takes over and keeps fermenting what sugar is left, making lactic acid, until the pH is down to about 3.

Flavor

In sauerkraut, Leuconostoc mesenteroides turns glucose into lactic acid, acetic acid and carbon dioxide. It also turns some fructose into mannitol, a sugar alcohol that tastes sweet, feels cool in the mouth and can hide bitterness. Given time, the bacteria ferment the mannitol into lactic acid as well.

That timing changes the result. In one taste test, most people preferred a partly fermented European sauerkraut to fully fermented kraut. The European kind held more leftover sugar, more mannitol and more ethanol, probably from wine added afterwards. But leftover sugar has a cost in bulk storage: spoilage organisms grow on it and gas builds up. A fully fermented sauerkraut has no sugar left and needs no further processing.

A second change can follow, called malolactic fermentation. Many strains of Leuconostoc and Lactobacillus turn malic acid, which vegetables contain naturally, into lactic acid and carbon dioxide. The gas causes trouble.

• In cucumbers it makes bubbles inside, softens the pickle, and gives hollow pickles known as "bloaters and floaters".
• In large tanks of sauerkraut it can cause heaving: the kraut swells fast with trapped gas and the brine level rises.
• Yet malic acid tastes harsher than lactic acid, and too much of it lowers how sauerkraut is rated, so producers must decide how far to hold this change back.

Sauerkraut tastes mainly salty, sour and sulfurous. Sulfur aromas belong to the whole cabbage family, radishes, kale and broccoli included, and fresh cabbage is rich in the compound that enzymes break down into many of sauerkraut's sulfur flavors. A little sulfur flavor is good; too much is not. Sauerkraut spiced with caraway is milder and less sulfurous, because the seeds seem to remove the starting material for some of the key sulfur compounds.

After fermentation

Spices, wine and other ingredients can be added to finished pickles for flavor. Cucumbers taken out of brine storage may be soaked or rinsed to make them less salty and less sour. Many pickles and krauts are pasteurized in their glass jars before they are sold.

A safety rule for sealed foods