It is not known when yeast was first used to bake bread; the earliest definite records come from Ancient Egypt. Researchers speculate that a mixture of flour meal and water was left longer than usual on a warm day and the yeasts that occur in natural contaminants of the flour caused it to ferment before baking. The resulting bread would have been lighter and tastier than the previous hard flatbreads. It is generally assumed that the earliest forms of leavening were likely very similar to modern sourdough; the leavening action of yeast would have been discovered from its action on flatbread doughs and would have been either cultivated separately or transferred from batch to batch by means of previously mixed (“old”) dough. Also, the development of leavened bread seems to have developed in close proximity to the development of beer brewing, and barm from the beer fermentation process can also be used in bread making.
Instant and active dry yeast are essentially the same ingredient, just in slightly different forms and applications. Consumers should keep sealed packets of both yeast types at room temperature and store partially used packets in an airtight container in the refrigerator. The main differences between the two are:
- Active yeast needs rehydration. Instant yeast can be mixed directly into dry ingredients, whereas active dry yeast must first be dissolved and rehydrated in warm water.
- Instant yeast needs less time to rise. Since instant yeast has a finer texture than active dry yeast, it’s possible to skip the initial rise time and shape loaves immediately after kneading. Loaves made with active dry yeast require longer rising times for the yeast to work its way through the dough.