Yeast

Baker’s yeast is a measured inoculum, usually sold as a packet or cake. It is not Wild yeast or a Sourdough starter; those are different leavening ecologies. Baker’s yeast is a bakery ingredient you weigh.

In baker’s percentage, flour is 100% and yeast is a percent of that flour weight, the same language as water and salt ¹. A formula that lists “1.2% yeast” is a dose, not a moral law. Scale the dough and the percentage stays; the grams change. See Baker's percentage.

Bread. Packaged yeast’s job is gas for rise. Fermentation in dough is still timed against gluten strength and the oven, whether the inoculum came from a packet or a starter ². Wheat flour is the food. The teaching Country loaf (teaching formula) uses starter instead of this ingredient; both are leavening choices, not interchangeable grams.

What to notice. Fresh yeast smells cleanly yeasty, not cheesy or dead. Dough should gain volume and a light, fermented smell. A packet is convenient; it does not teach you what the dough is doing. Watch the dough.

Sourdough uses a living culture rather than a packet of baker’s yeast. Wine yeast on grape must is another habitat; the same word does not make the organisms or processes interchangeable.