Salting foods, trading bacteria: the business of fermentation continues to ripen

Sandor Katz's kitchen is an alchemist's laboratory. Glass jars filled with grains and spices both common and unusual — oat groats and rice, millet and dried tapioca pearls, sugar and licorice, dulse and mauby bark — line ceiling-high shelves.

Beneath them sit carboys filled with homemade meads, fruit wines and perry. In glass jars and ceramic crocks on the broad central table, the alchemist's assistants — trillions of bacteria — transform red cabbage into crisp sauerkraut with a hint of caraway, deep green summer cucumbers into fizzingly sour olive-colored pickles, carrots and green cabbage into bracing pao cai (Chinese pickles), and sliced daikon radish into an extraordinary kimchi.

Fermentation is the world's oldest method of storage and preservation. It arose out of practicality. It is easiest to grow cabbages, and other crops, if you synchronize the planting and harvesting; but you cannot eat them all at once. If you shred, salt and pack those same cabbages in jars they will last more or less indefinitely, and, in the process, become much tastier.

People tend to think of fermented foods as pickly and sour. In fact, bread, cheese, yogurt, chocolate and tea all undergo fermentation. In bread, though, as in chocolate, the microbes are dead at the point of consumption. Unpasteurized sauerkraut, kimchi and kombucha, on the other hand, teem with live bacteria.

To biologists, fermentation is the anaerobic metabolizing of sugars. It is what the yeast used to make bread, beer and wine does when it turns carbohydrates into alcohol and carbon dioxide without the benefit of oxygen. But not all the processes in Katz's kitchen are anaerobic. Tempeh, a Javanese food made from soy beans inoculated with spores of Rhizopus, a parasitic fungus, requires air to circulate if the mold is to grow into a solid cake around the beans. In his book "The Art of Fermentation," Katz prefers a broader definition: "the transformation of food by various bacteria, fungi and the enzymes they produce."

Not all microbial transformations are desirable. Leave a head of cabbage in brine for a week or a month and you will have delicious sauerkraut. Leave it on the kitchen counter for a month and you will have a slimy mess.

But the line between fermented and rotten is not always so stark. With the exception of some Nordic types, Westerners tend to be repulsed by fermented fish. But they will happily eat stinky, fermented milk in the form of Gorgonzola or Stilton. Many East and Southeast Asians, who consume fish sauce regularly, eschew cheese.

Katz teaches fermentation workshops around the world to strangers who come together to salt and squeeze root vegetables and trade SCOBYs (a "symbiotic colony of bacteria and yeast" — the broad, slimy, vaguely organ-like disc that turns tea and sugar into kombucha).

Fermentation connects humans to the invisible processes of life — to the microbes that were here for billions of years before humans arrived, and will persist for billions more after they have gone. Fermentation enlists the microbes' aid, proceeds on their schedules, succeeds or fails according to their needs and rules.

The oneness goes deeper than that. People are not unitary beings; they are entire universes for the "microbiomes" that live on and within them. The gut bustles with bacteria by the trillion which assist with digestion, helping determine health, weight and even mood.

Nearly everyone on Earth consumes some form of fermented food regularly. The revival of interest in the West is in part a return to the norm; in the 20th century much of Europe and the United States descended into peculiar ignorance on the subject.