Yeast

Yeast is a single-celled fungus sold as beige granules or moist cream-colored blocks. It produces carbon dioxide that lifts dough and lends a warm, bready aroma; bakers use it to leaven breads, pizza, and enriched doughs. Sold as active dry, instant, or fresh/compressed forms, each behaves slightly differently in hydration and fermentation speed.

Domesticated strains of Saccharomyces cerevisiae emerged alongside early bread and beer traditions in Southwest Asia and North Africa, then spread widely through Europe. Commercial pressed yeast grew in the 19th century with industrial fermentation, and instant dry yeasts became common in the mid-20th century; today baker's yeast is produced globally.