Fermentation: yeast, bacteria and flavor

Main types

• Yeast (bread, beer): sugar to CO2 and alcohol.
• Lactic-acid bacteria (sauerkraut, kimchi, yogurt, sourdough): sugar to lactic acid, lowering pH so spoilage organisms struggle.
• Molds (koji for soy sauce, miso and sake).

Vegetable ferments: salt matters

Sauerkraut is commonly made with about 2-2.5% salt by weight of cabbage, kept submerged under brine. Too little salt invites softening and spoilage. White film (kahm yeast) is common; fuzzy mold of colors, or slimy, foul-smelling batches go in the trash.

Use tested procedures

Follow the National Center for Home Food Preservation for ferments and pickles. Never improvise low-acid garlic-in-oil or canning recipes; botulism is a real risk.

Ask your bot about the science

Explain fermentation in plain English for a home cook, with one kitchen experiment I can do to see it, and how it applies to [dish].
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Where these facts come from

• American Chemical Society: Reactions, food chemistry explainers
• Exploratorium: Science of Cooking
• USDA FSIS: Safe temperature chart
• FoodSafety.gov: Safe minimum internal temperatures
• Harold McGee, On Food and Cooking (Scribner, 2004): the standard reference on kitchen chemistry

Checked Oct 29, 2026. Temperatures given for reactions are typical ranges, not sharp switches; they shift with moisture, pH and time. Food-safety numbers always come from USDA/FoodSafety.gov.