Fermentation: how yeast and bacteria make flavor
Intermediate Kitchen science
Fermentation is microbes eating sugars and starches and turning them into gas, acid, alcohol and new flavors, as in bread, yogurt, sauerkraut and miso.
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How do you do it?
- Rise bread dough slowly in the fridge for 12-72 hours for deeper, more complex flavor.
- For sauerkraut, mix shredded cabbage with salt at about 2% of its weight and keep it pressed under its own brine.
- Keep homemade ferments at a cool room temperature, around 60-75°F, and follow a tested recipe.
- Discard ferments with fuzzy mold, pink or slimy patches, or a rotten smell; a clean sour smell is normal.
Why does it work?
Yeasts and bacteria feed on sugars and leave behind byproducts. Baker's yeast makes carbon dioxide, which raises bread, plus small amounts of alcohol and aroma compounds. Lactic acid bacteria, which make yogurt, sauerkraut and sourdough tang, produce lactic acid. That acid lowers the pH enough that most spoilage microbes cannot grow, which is why fermenting preserves food. Salt in vegetable ferments holds back unwanted microbes while the salt-tolerant lactic bacteria thrive. Slow, cool fermentation gives microbes and enzymes more time to break down proteins and starches into flavorful pieces.
What are the common mistakes?
- Letting vegetables poke above the brine — mold grows on exposed pieces.
- Using too little salt — vegetables turn soft and unwanted microbes take over.
Still stuck? Watch someone do it on YouTube.
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