Yeast needs food, warmth, and moisture to make your doughs rise. But yeast cells are fussy about temperature.
One of the first things that make an impression on you as you get into baking is that yeasts—the single-celled organisms that leaven doughs—are very picky about temperature.
The yeasts feast on the starches and sugars in the flour, churning out ethanol and tiny bubbles of carbon dioxide. The alcohol improves the aroma and flavor of your bread in many ways, and the gas bubbles get trapped by the gluten in the dough, leavening the loaf and making it airy.
But commercially sold yeast is dehydrated and dormant. For it to become active, they need to be rehydrated and revived with moisture and warmth.
This why we make doughs by adding lukewarm water to the dough mix. It’s also why the water must neither be too cold or too hot. So let’s talk about the temperature of the water that’s “just right.”
How to Activate Yeast
Three types of yeast are used in baking: fresh yeast, active dry yeast, and instant yeast.
Think of fresh yeast and active dry yeast as being in a state of deep sleep; you need to wake up the yeast cells before they start feeding on the sugars and starches in your dough.
Instant yeast is in a state similar to a nap. It wakes up fairly quickly, so you don’t have to activate it first; just work the instant yeast granules into the flour, add water, and mix with your hands to incorporate.
At What Temperature Does Yeast Activate?
| Yeast Type | Activation Method | Water Temperature |
|---|---|---|
| Fresh yeast | Dissolve in 2x its weight in lukewarm water | 70-90ºF (21-32°C) |
| Active dry yeast | Dissolve in 4x its weight in warm water | 100-110°F (38-43°C) |
| Instant yeast | Not necessary; add the yeast directly to the dough mix | 100-130°F (38-54°C) |
Fresh yeast, which is highly perishable and must be refrigerated for up to 1-2 weeks or frozen for up to 1 year, activates at a temperature of 70ºF to 90ºF (21°C to 32°C). Before being added to the dough mix, fresh yeast should be activated by being dissolved in twice its weight in warm water.
Active dry yeast, which should be kept at cool room temperature unopened and stored in the fridge or freezer after opening, activates at temperatures in the range of 100°F to 110°F (38°C to 43°C). Before being added to the dough mix, active dry yeast should be activated by being dissolved in four times its weight in warm water.
Instant yeast, which can be kept in the pantry unopened and be refrigerated or frozen after opening, activates at temperatures between 100°F and 130°F (38°C and 54°C). Instant yeast does not need to be rehydrated before use; it can be added directly to the dough.
Yeast cells die at temperatures above 130°F (54°C), so think twice about mixing yeast with water that feels uncomfortably hot. If you use water that’s too hot, the yeast cells will be killed and your dough won’t rise.
Which Type of Yeast Should You Use?
If you want to develop the aroma and flavor of the dough, use fresh yeast. It ferments the dough slowly, producing bread loaves with a rich smell and complex flavor.
In Professional Baking, 7th Edition, bestselling cookbook author Wayne Gisslen writes that ¼ of the yeast cells in active dry yeast are dead because of the harsh drying process used to produce it.
This, Gisslen adds, can have a detrimental effect on the aroma and flavor profile of your bread, which is why this type of yeast isn’t really popular with bakers. Still, as far as home cooking is concerned, active dry yeast is perfectly fine as a substitute for fresh yeast if that’s all you can get your hands on.
Instant yeast makes doughs ferment quickly and with plenty of gas bubbles. Use it when you are short on time or want to make bread that’s airier than usual. Just make sure the dough doesn’t overleaven; otherwise, it will lose its structure.
Does the Chemistry of Tap Water Affect Yeast?
In his 2009 book Keys to Good Cooking, a countertop companion for the home cook, American culinary author Harold McGee explains that the chemicals in your water can have an adverse effect on the properties of your doughs.
Acidic water, McGee says, weakens the gluten in the dough, and heavily chlorinated water can slow down the growth of yeast—and so your homemade loaves of bread will take longer to rise once you’re done with the kneading.
Even if you used water at just the right temperature, allow a little bit more time for the yeast to activate and the dough to rise in the case that your community has highly chlorinated tap water.
