Sourdough fermentation
Leavening and acidification of dough by wild yeasts and lactic acid bacteria in a symbiotic culture, giving sour flavor and slow rise.
Lactic acid bacteria: Bacteria that ferment sugars into lactic acid; in sourdough they acidify dough and shape flavor. The dominant partners in sourdough, producing the acids that sour and preserve the dough.
Sourdough starter: A maintained flour-water culture of wild yeast and lactic acid bacteria used to leaven bread. The living vehicle carrying the fermentation into each new batch of dough.
Ancient Egyptian bread: Leavened bread baked in Egypt by roughly 3000 BCE, the earliest well-documented risen loaves. The earliest firm evidence of dough raised by wild fermentation.
San Francisco sourdough: A tangy white loaf defined by Lactobacillus sanfranciscensis, identified in local bakeries in 1970. The best-studied sourdough, whose bacterium was named after the bread itself.
Baker's yeast: Cultivated Saccharomyces cerevisiae used for fast, neutral-tasting dough leavening. The fast, flavorless industrial rival that sourdough fermentation replaced for most bread.
Saccharomyces exiguus: A wild yeast common in sourdough starters that raises dough but cannot metabolize maltose. Its inability to use maltose leaves sugars for the bacteria, underpinning the partnership.
Gluten network: The viscoelastic protein web in wheat dough that traps fermentation gas and holds the crumb open. Sourdough gas must be caught by this web for the loaf to rise.
Barm: Foam skimmed from fermenting beer, used as a yeast source for baking before compressed yeast. The brewer's alternative that displaced sourdough leavening in much of Europe.
Rye bread: Dense breads from rye grain, traditionally leavened and acidified by sourdough. Acidity is functionally required there: rye pentosans demand acid to set the crumb.
Baking soda: A chemical leavener releasing carbon dioxide on reaction with acid, with no fermentation. Leavening without microbes or time, the opposite pole from slow wild fermentation.