Jästa

Jästa is a Swedish verb meaning to ferment or to let dough rise as a result of fermentation. It is commonly used in baking and brewing to describe how leavening and flavor development occur during the processing of dough, batter, must or wort. The related noun jäst refers to yeast, the microorganism most often responsible for the fermentation that causes bread dough to rise.

In bread baking, the most common fermenting agent is baker's yeast, typically Saccharomyces cerevisiae. Yeast consumes sugars in the dough and produces carbon dioxide and alcohol. The carbon dioxide forms bubbles that inflate the dough, making it lighter and giving bread its texture. Lactic acid bacteria may be present in sourdough cultures, contributing tangy flavors and additional acidity. Temperature, sugar availability, salt content, and dough hydration influence the rate and outcome of jästa.

Common techniques include allowing the dough to rise at suitable temperatures (proofing), sometimes referred to as jäsa. Bakers may choose slow, cold fermentation (kalljäsa) to develop flavor, or use quicker fermentation with warmer conditions or active dry yeast (torrjäst) or fresh yeast (färsk jäst). Proper kneading and fermentation management help develop structure and aroma.

Safety and quality depend on hygiene and correct handling. Fermentation should show signs of activity such as bubbling and a pleasant aroma. Off smells, unusual sliminess, or visible mold indicate spoilage and the product should be discarded. Jästa is also used in brewing and other fermentation contexts, where yeast or microbes transform sugars into alcohol and other byproducts.