Dry Yeast vs. Fresh Yeast: What’s the Difference?

Yeast is a single-celled organism that exists all around us, especially on the surface of grains (like wheat flour) and fruits (like grapes). When activated by water, yeast starts to consume the sugar in grains and fruit, and it releases carbon dioxide gas as a byproduct.

In bread dough, this gas fills the gluten structure and causes dough to rise. Although there are hundreds of different species of yeast, Saccharomyces cerevisiae is the most famous, known for its role in both baking and brewing.

Although yeast is plentiful in the natural environment, when it comes to baking bread, most recipes call for one of four types of yeast.

1. 1. Active dry yeast: If a bread recipe calls for yeast, this is probably what it means. The most widely available type of yeast, active dry yeast changed the way we bake when it was invented in the early twentieth century. It consists of yeast granules covered with a protective coating. The yeast is dormant until it is activated by warm water.
2. 2. Instant yeast: In the 1970s, changes were made to dry yeast to make it dissolve faster. The resulting instant yeast could be added directly to dry ingredients without prior activation. Both professional and home bakers use instant yeast for its ease and reliability (active dry yeast is notorious for dying out before it hits its expiration date).
3. 3. Cake yeast: Also known as compressed yeast, this fresh yeast consists of blocks of moist, living yeast cells. Highly perishable, cake yeast can be stored in an airtight container in the refrigerator for up to two weeks. Find it in the refrigerated section of well-stocked grocery stores.
4. 4. Sourdough starter: Most people don't think of a sourdough starter (aka levain) as a type of yeast, but that's exactly what it is. While both fresh and dry commercial yeasts are made with particular strains of Saccharomyces cerevisiae chosen for their bread-rising ability, a sourdough starter is made of naturally occurring wild yeasts. It can last indefinitely, but it requires consistent maintenance.

There are four key differences between dry yeast (both active dry yeast and instant yeast) and fresh yeast (or cake yeast).

1. 1. Texture: Fresh compressed yeast has a moist, crumbly consistency, like a block of feta cheese. Dried yeast—both active dry and instant—looks and feels like sand or cornmeal.
2. 2. Shelf life: Both instant and active dry yeast have much longer shelf lives than fresh yeast. Active dry and instant yeast remain usable for several months when stored at room temperature, while fresh yeast must be used within a week or two and shouldn't leave the fridge. Instant yeast has the lowest moisture content of the three commercial yeasts, and it therefore has the longest shelf life.
3. 3. Activation: Active dry yeast requires a proofing or blooming step before it can be incorporated into dough. This involves combining the dry yeast granules with warm water and whisking until bubbles appear. Both fresh yeast and instant yeast skip this step.
4. 4. Rising time: The drying process involved in producing active dry yeast kills about a quarter of the yeast cells. Those dead yeast cells form a protective coating around the living cells, slowing down fermentation and producing a noticeably yeasty flavor. Fresh yeast and instant yeast contain more living yeast cells, so they produce more carbon dioxide than active dry yeast, resulting in a bigger, faster rise.

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