What is Yeast?

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Yeast is the leavening agent in bread, dinner rolls, pastries, and similar products.

Fermentation is the process by which yeast acts on sugars and changes them into carbon dioxide gas and alcohol. This release of gas produces the leavening action in yeast products. The alcohol evaporates completely during and immediately after baking.

Types of Yeast

  1. Fresh yeast, also called compressed or cake yeast is moist and perishable and is preferred by professional bakers. This yeast comes in a solid, clay-like block. Professional bakers tend to say this yeast is the best yeast for bread because it adds a more robust flavor. To use, crumble it and let it soften and dissolve in whatever liquid the recipe calls before adding it to your ingredients.
  2. Active dry yeast is a dry, granular form of yeast. Active dry yeast must be rehydrated in 4 times its weight of warm water before use. When using active dry yeast in a bread recipe, use part of the water in the formula to dissolve the yeast. Do not add additional water.
  3. Instant dry yeast is also a dry granular form of yeast, but it does not have to be dissolved in water before use. It can be added in its dry form because it absorbs water much more quickly than active dry yeast. It also produces more gas than active dry yeast, so less of it is needed. Instant dry yeast is sometimes called rapid-rise or quick-rise yeast.


From fresh yeast to instant dry yeast

To convert from fresh yeast to instant dry yeast, multiply the fresh quantity by 0.33. Instant yeast can be incorporated into the dough without first rehydrating.

From fresh yeast to active dry yeast

To convert from fresh yeast to active dry yeast, multiply the fresh quantity by 0.4. Active dry yeast must be hydrated in warm water before being incorporated into a dough. 

From instant dry yeast to active dry yeast

To convert Instant yeast to active dry yeast in a recipe, multiply the amount of instant yeast by 1.25. You will need to round up figures, sometimes.

1 teaspoon instant yeast = 1¼ teaspoons active dry yeast.

From active dry yeast to instant dry yeast

To convert active dry yeast to instant yeast in a recipe, multiply the amount of active dry yeast by 0.75. You will need to round up figures, sometimes.

1 teaspoon active dry yeast = ¾ teaspoon instant yeast.

What can go wrong?

When bread doesn’t rise, it can be one or more of several reasons.

The yeast was dead before you used it.

When you open a package of yeast, it should smell earthy and yeasty. If it doesn’t you can test or proof the yeast’s liveliness by combining it with some of the warm water from the recipe and a pinch of sugar. If the yeast is active, it will produce a bubbly mass within 10 minutes.

The liquid used was too cold or too hot.

Water below 21 degrees Celcius (70F) may not be warm enough to activate the yeast, but rising the dough in a warm room will activate it just might take several hours. Water that’s too hot can damage or kill the yeast. The damage threshold is 37 degrees Celcius (100F) for cake yeast, 48C (120F) for active dry, and 54C (130F) for instant yeast.

Too much salt was added or added too early.

Adding salt before the yeast has had a chance to multiply can dehydrate it, starving it of the water it needs to survive.

The dough was not punched down or stirred enough.

This allows alcohol to build up and poison the yeast.

How much yeast do you really need?

The exact amount of yeast needed to rise bread dough depends on three things:

  1. The type of yeast used. You need about twice as much as cake yeast as active dry or instant dry yeast to rise the same weight of the dough.
  2. The temperature of the dough. Higher temperature makes the yeast more active, so you don’t need to use as much yeast in a warm environment. You also don’t need to use as much yeast in a cold environment if you’re doing a long, slow rise; the only time you need more yeast would be for a quick rise in a cold environment.
  3. The length of rising time. The slower the rise, the less yeast you need. You can control rising times to fit your schedule by varying the amount of yeast and the temperature of the rise.


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