jästen

Jästen is the Swedish term for yeast, a diverse group of unicellular fungi that are widely used in food production and fermentation. In everyday usage, jästen most often refers to baker's yeast (Saccharomyces cerevisiae), but many other yeasts participate in natural fermentations such as sourdough, beer, and wine.

Biology: Yeasts are eukaryotic microorganisms that typically reproduce by budding. They are facultative anaerobes, able to grow with or without oxygen, and many species ferment sugars to produce ethanol and carbon dioxide, which leavens dough or drives alcoholic fermentation.

Applications: In baking, jästen converts sugars in dough into carbon dioxide and ethanol, causing the dough to rise. In brewing and winemaking, yeast ferments sugars to alcohol. The most common baking and brewing species is Saccharomyces cerevisiae; lager yeasts belong to Saccharomyces pastorianus. Wild yeasts contribute to the flavor and complexity of some fermentations, such as sourdough and natural wine or beer.

Forms and sources: Yeast for home use is sold as fresh (creamy blocks), active dry yeast, or instant (rapid-rise) yeast. Wild or cultivated strains may be used in sourdoughs and specialty fermentations. Probiotic yeasts, such as Saccharomyces boulardii, are used in some dietary supplements and medical contexts.

Storage and safety: Commercial jästen is considered safe for food use. Store in a cool, dry place; refrigeration is recommended for some products after opening. In controlled fermentations, specific strains are chosen for flavor, aroma, and performance.