Baker's yeast

One US cup of baker's yeast weighs 148 grams. Going the other way, 100 grams is about 0.68 cups.

Yeast for baking comes in three forms in common use — active dry, instant, and fresh (cake) yeast — and this entry covers the two dried forms, which measure essentially the same by weight per cup. Active dry yeast has slightly larger granules that traditionally need proofing in warm water before use; instant yeast has finer granules that can be added directly to the flour. Both are the same organism, Saccharomyces cerevisiae, dried to preserve activity, and both weigh close to 3.1 grams per teaspoon or 148 grams per cup.

USDA FoodData Central publishes 1 cup of active dry yeast at 148 grams (FDC 368813, Yeast, baker's, active dry). That gives a bulk density of 0.6255 grams per millilitre. King Arthur's ingredient weight chart publishes instant yeast at 3 grams per teaspoon (from three different partial-cup measurements, all consistent), which extrapolates to 144 grams per cup and 0.6086 grams per millilitre. The two figures agree within 2.7 percent, well inside the 10 percent tolerance we apply to the milled category.

The substitution ratio between the two dried forms is 3:4 by volume — 3 parts instant equals 4 parts active dry — but this reflects a difference in leavening potency, not a difference in weight. Instant yeast is somewhat more concentrated per volume because the finer granules pack more densely per teaspoon and because more of each granule is exposed and active. Per gram, instant is modestly more effective at leavening than active dry, though the exact ratio varies by manufacturer.

Fresh yeast (also called cake yeast or compressed yeast) is a different product not covered by this entry. It is approximately 70 percent water and much less dense in a measuring cup than dried yeast, though it is rarely measured by volume because it comes in solid blocks. The conventional substitution is 3 grams fresh yeast equals 1 gram active dry yeast equals 0.75 gram instant yeast.

Standard US supermarket packaging for dried yeast is the 1/4 ounce (7 gram) individual packet and 4 ounce (113 gram) jars. Most home baking recipes calling for 'one packet' mean 7 grams, which is 2 1/4 teaspoons of either active dry or instant. When a recipe calls for 'yeast' without specifying which type, active dry is the more common assumption in older American recipes and instant is more common in modern European and professional recipes.

Baking practice differences: active dry yeast should be proofed (dissolved in warm water at 40-43°C for 10 minutes) before mixing to confirm the yeast is alive and to soften the granules. Instant yeast can be added directly to the dry ingredients and hydrates as the dough is mixed. Some modern sources argue that active dry yeast no longer needs proofing because manufacturers have reduced the granule size enough that it hydrates on its own; the traditional proofing step still works and does not hurt.

Related products this entry does not cover: nutritional yeast (deactivated yeast used as a savoury seasoning, has no leavening power and different density around 100 grams per cup), brewer's yeast (used in beer brewing, similar organism but different processing), and wild yeast starters (naturally occurring cultures used in sourdough, not commercially standardised and not measured by weight in the same way).

FDA regulates baker's yeast under general food safety rules and permits its use as a direct food additive under 21 CFR 172.896 (Yeast preparations). Codex Alimentarius does not have a specific standard for baker's yeast. Neither publishes a bulk density.

The category here is 'milled' because dried yeast behaves like other fine granular powders in a measuring cup — it clumps slightly, bridges over air pockets, and its density depends on scoop method. The 10 percent tolerance applies. Both sources sit well inside it.