Yeast Conversion Chart: Fresh, Active Dry and Instant, With the Actual Factors

The factors are approximate, and the manufacturer beats the chart

0.4 and 0.33 are general guidelines, not physical constants. What they encode is roughly this: fresh yeast is about 70 percent water, so most of what you weigh is moisture, while dry yeasts are around 5 to 8 percent water and correspondingly concentrated. But strains differ, drying processes differ, and the live cell count per gram differs between brands by more than the difference between the two dry types. King Arthur, whose professional reference is where these two numbers come from, says outright that it is best to follow the conversion ratio provided by the manufacturer. If the sachet in your hand prints a ratio, use that one.

The chart also hides a small dough-yield problem that professional bakeries fix and home bakers never notice. When you replace 42 g of fresh yeast with 13.9 g of instant you have removed 28 g of mass from the dough, most of it water. On a single loaf that is nothing. On a 20 kg mix it is enough to change the hydration, and most yeast manufacturers advise making up the weight difference between dry and fresh with additional water. If you are scaling a formula up and the dough suddenly feels tighter than it used to, this is why.

Active dry needs water first; instant does not — and that is the real difference

Active dry yeast is dried in larger granules with a layer of dead cells on the outside, and it must be hydrated in warm water before being incorporated into a dough. Instant yeast is dried faster into finer particles that rehydrate on contact, so it can be mixed straight into the flour. Modern active dry has improved enough that dumping it dry into a well-hydrated dough usually works anyway, but usually is doing a lot of work in that sentence: in a stiff, low-hydration dough such as bagels at 52 percent water, undissolved granules genuinely do underperform.

If you do rehydrate, use water around 105 to 110 °F, take it from the recipe's water rather than adding extra, and keep it away from the salt and the sugar until it has dissolved. Water hotter than about 130 °F starts killing yeast, and ice-cold water is a problem for instant in particular — it is sensitive to ice, so if your dough water is very cold it is better to mix for a minute or two before adding the yeast. The old ritual of watching for foam is not a rehydration step, it is a freshness test, and it is worth doing on any packet that has been open in the fridge for months.

Converting the amount is the easy half; the time is the other half

A converted dose gives you the same gas production only if everything else is equal, and in a home kitchen it never is. Fermentation rate roughly two-and-a-half times for every 18 °F of dough temperature, which means a 5 °F difference between two kitchens moves the rise time more than the difference between a well-converted and a badly converted yeast dose. If your substituted dough is running fast or slow, look at the thermometer before you blame the arithmetic.

The most useful habit here is to stop thinking in grams of yeast and start thinking in percent of flour, because that is the number that transfers between recipes. Twenty grams of fresh yeast means nothing until you know it was on 1 kg of flour, at which point it is 2 percent fresh — or 0.8 percent active dry, or 0.66 percent instant. Written that way, you can drop the dose onto any batch size, and you can compare two recipes from two countries at a glance instead of doing three conversions in your head.

Frequently asked questions

Can I use instant yeast in a recipe that calls for active dry, one for one?

You can, and the dough will simply rise a bit faster, because instant is about 21 percent stronger per gram — the correct factor is 0.825, so 7 g of active dry is 5.8 g of instant. On a loaf with a two-hour rise that difference shows up as maybe fifteen or twenty minutes, which most recipes absorb without complaint. Where it matters is anything proofed on a schedule you cannot move, such as pizza dough timed to a party, or a long cold ferment where a fast start eats the flavour development you were paying for.

How many grams is a teaspoon of dry yeast?

About 3 g for a level teaspoon, which is the figure the calculator uses, and the standard 1/4 oz packet holds 2 1/4 teaspoons, or roughly 7 g. Volume measures of yeast are the weakest link in any bread recipe: granule size differs between active dry and instant, and a heaped spoon can carry half again as much as a level one. On a formula where the yeast is 1 percent of the flour, being one gram out on a small loaf is a 20 percent error in the dose. Weigh it if you own a scale that reads to 0.1 g; if you do not, level the spoon carefully and accept a wider window on the rise time.

Can I substitute sourdough starter for commercial yeast with a factor?

No, and any chart that offers you one is selling a convenience that does not exist. Commercial yeast is a single selected strain at a known and consistent cell count; a starter is a live culture of wild yeasts and lactic bacteria whose activity depends on how recently it was fed, at what temperature, and at what hydration. The usual working substitution is structural rather than arithmetic: replace the yeast with 20 percent of the flour weight as starter at 100 percent hydration, subtract that starter's flour and water from the main dough, and expect the bulk to take three to four times as long. The bread will also taste different, which is the reason to do it.