Fresh, active dry and instant yeast: what is actually different
They are the same organism — Saccharomyces cerevisiae — preserved in three different ways, and the only thing you need to convert between them is water content. Fresh (cake or compressed) yeast is about 70% moisture and must be kept cold; active dry yeast is dried into granules with a protective coating of dead cells, which is why it should be rehydrated; instant yeast (also sold as rapid-rise, fast-action or bread-machine yeast) is dried more gently into finer particles that dissolve straight into the dough. The standard baking-school equivalence by weight is:
fresh 3 : active dry 1 : instant 0.75
Fresh yeast is roughly three times the weight of instant yeast for the same leavening power, and instant is about 25% less than active dry. Some bakery calculators print fresh : active dry : instant as 3 : 1.25 : 1, which is slightly more generous with active dry; the 3 : 1 : 0.75 rule used here follows the standard framing that instant yeast replaces active dry at 75% and fresh yeast at three times its weight. Either way, exact grams matter far less than dough temperature and time.
So 1 gram of active dry yeast equals 3 grams of fresh yeast or 0.75 grams of instant. Going the other way, 7 g of instant yeast is 9.3 g of active dry or 28 g of fresh. Teaspoons are a rougher measure: one teaspoon of active dry or instant yeast weighs about 3.1 g, and a US envelope holds 7 g — exactly 2¼ teaspoons. A fresh cake is usually 17 g (0.6 oz).
Using the converter
Tell the tool which yeast you have and how much, and it prints the equivalent of the other two, plus the sourdough starter conversion. The dough helper underneath answers the more common question — how much yeast for 500 g of flour? — using the usual ranges: roughly 1.75% instant yeast by flour weight for a fast, sweet dough that rises in about an hour, 1% for a normal two-to-three-hour rise, and 0.4% for an overnight cold ferment. Those are starting points, not rules: a cold kitchen, heavy sugar or fat, or an old packet all slow the rise, and the fix is time, not more yeast.
Practical notes that matter more than the ratio
- Active dry needs waking up. Proof it in 100–110°F (38–43°C) water with a pinch of sugar for 5–10 minutes; if it foams, it is alive. If it does nothing, no amount of extra yeast will save the dough.
- Instant goes straight in. No proofing needed, and it tolerates being mixed with the flour and salt from the start.
- Temperature, not quantity, controls timing. Doubling the yeast does not halve the rise time — it just makes the dough taste yeasty. A 10°F (5°C) warmer kitchen can cut a rise nearly in half.
- Watch the water. Above about 120°F (49°C) yeast starts dying; 130°F (54°C) kills most of it. Cold water is slow but safe.
- Salt is not the enemy, but contact is. Salt at 2% of flour weight strengthens gluten and controls the rise; just keep it out of direct contact with the yeast before mixing.
- Storage: unopened dry yeast keeps for about two years; once opened, keep it in an airtight jar in the fridge or freezer and expect it to lose roughly 10% of its power a year.
Sourdough starter instead of commercial yeast
A 100%-hydration starter (equal weights of flour and water) contains wild yeast plus lactic acid bacteria, so it leavens slowly and adds sourness. As a working rule of thumb, about 240 g — one cup — of active starter replaces 7 g (2¼ tsp) of instant yeast, which lands close to the widely used shortcut of “starter equal to about 20% of the flour weight”. Be aware that starter conversions are approximations rather than standardised equivalents — King Arthur Baking warns that sourdough starter cannot simply be swapped in 1:1 — so taste the dough and adjust the rise time rather than treating the number as exact. Because the starter is half flour and half water, subtract its weight from the recipe: 240 g of starter means removing about 120 g of flour and 120 g of water. The dough will then need far longer to rise — four to eight hours at room temperature, or overnight in the fridge — and the sourness increases with that time. The converter above gives the exact starter weight for whatever your recipe calls for.
Frequently asked questions
How much instant yeast equals 7 g of fresh yeast?
About 1.75 g. The standard ratio is fresh : active dry : instant = 3 : 1 : 0.75, so 7 g of fresh yeast is 2.33 g of active dry or 1.75 g of instant — just over half a teaspoon. This is why recipes written for fresh yeast look like they use a lot.
How much fresh yeast replaces one packet of dry yeast?
A 7 g packet of active dry yeast equals 21 g of fresh yeast by the 3 : 1 rule, and a 7 g packet of instant equals 28 g of fresh. Compressed yeast cakes are commonly sold in 17 g (0.6 oz) blocks, so most recipes need one and a half to two cakes. Note that some manufacturers' charts treat one 17 g cake as equal to a full 7 g packet of active dry (a 2.4 : 1 ratio) - that is more generous than the weight-based rule here; if your recipe comes from a manufacturer, follow their figure.
Is instant yeast the same as active dry yeast?
They are the same species dried differently. Instant is finer, dries faster, dissolves straight into the dough and contains slightly more live cells, which is why it is used at 25% less than active dry by weight (0.75 : 1). Active dry has a coarser coating and is best proofed in warm water first.
How much yeast for 500 g of flour?
About 5 g of instant yeast (roughly 1% of the flour weight) for a two-to-three-hour rise, 8 to 9 g for a fast sweet dough, or 2 g for an overnight cold ferment. In fresh yeast that is 15 g, 25 g and 6 g respectively.
Can I just double the yeast to make the dough rise faster?
It speeds things up less than you would expect and leaves a yeasty, slightly bitter taste, and the dough can over-proof and collapse. Temperature and time are the real controls — 5°C (10°F) warmer halves a rise far more reliably than extra yeast.
How much sourdough starter replaces a packet of yeast?
About 240 g (one cup) of active 100%-hydration starter replaces 7 g of instant yeast - close to the common shortcut of starter at about 20% of the flour weight. Since starter conversions are approximations rather than standardised equivalents, treat this as a starting point. Because that starter is half flour and half water, subtract roughly 120 g of flour and 120 g of water from the recipe, and expect a much longer, slower rise.
Does yeast expire, and how do I test it?
Unopened dry yeast keeps about two years past the printed date if stored cool and dry. To test it, stir a teaspoon into 50 ml of 38–43°C water with a pinch of sugar: foam within 10 minutes means it is alive, and if nothing happens, buy new yeast rather than adding more of the old.
The 3 : 1 : 0.75 relationship between fresh, active dry and instant yeast is put to work in How a cold ferment really works.