Demystifying Yeast

Inspired by conversations on the Food52 Hotline, we're sharing tips and tricks that make navigating all of our kitchens easier and more fun. Today, we're talking about yeast in all its forms.

Yeast can be scary: It's alive. It magically turns flour and water into bread. And when we really need it to deliver, it lays dormant in defiance. It's fickle, and sometimes needy. But understanding this mysterious little organism is the first step to mastering it, and thereby getting more comfortable with baking bread in your own kitchen.

History
The strain of yeast we use, Saccharomyces cerevisiae, could be called humanity's oldest pet. The world's "oldest domesticated organism", according to King Arthur Flour, has been helping us bake bread and brew beer for thousands of years, and is just one of 1,500 identified strains of yeast. Its name literally translates to “sweet fungi of beer.”

How it works
Yeast, as we've said, is a living organism, and spends most of its time reproducing and eating. When combined with water, flour, and warmth, it converts sugars and starches into CO2, alcohol, and natural acids; this process is called fermentation. As Peter Reinhart explains it, yeast acts just like humans do: it eats, belches, and sweats. 

The natural acids and alcohol given off by yeast's fermentation give bread flavor; the CO2 gives it structure. Mixing wheat flour with water and kneading the resulting dough creates a network, or web, of proteins -- called gluten -- that trap these gasses. The CO2 then causes the dough to expand and fill like a balloon, which causes your dough to rise.

Playing well with others 
What affects how well yeast works? Food, moisture, pH, and warmth all contribute to a productive environment. Salt and too much sugar, on the other hand, can both slow yeast activity. Salt is used in bread recipes not only to add flavor, but also to regulate yeast activity -- it'll keep your yeast in line by keeping it from acting too quickly.

What went wrong?
Anyone who has tried their hands at yeast bread understands the disappointment of a dough that doesn't rise. The main cause of inactive or dead yeast is too much time on the shelf, poor storage conditions, or mixing with water that's too hot. So it's important to buy fresh, good quality yeast; store it properly (see below for that one); and be sure that you mix it with warm, not hot, water.

Types of yeast
Saccharomyces cerevisiae can be found commercially in three different forms: Fresh, Active Dry, and Instant.

Fresh: Fresh yeast was the first commercially-produced type of yeast. It is comprised of 100% living cells and is 70% water by weight. Fresh yeast produces the most C02 during fermentation of any commercially available yeast, making it strong and fast-acting. Some people claim that fresh yeast also creates a better-tasting bread. While very reliable, it is also quite perishable, and can be hard to find. It dissolves easily when mixed with water or rubbed with sugar, and does not need to be proofed.

Active Dry: Manufacturers discovered a way to dry out yeast cells in the 1860s, and Active Dry Yeast was born. It is 95% dry matter. Traditionally, only 30% of the cells were alive, with the dead cells forming a barrier around them; this made it necessary to proof the yeast in warm water to activate the live cells before adding other ingredients. These days, the drying process is gentler, and most Active Dry Yeasts can be mixed directly into other ingredients, according to King Arthur Flour. 

Instant: Instant yeast has the same water content as Active Dry, but the drying process is less harsh, meaning that proofing is unnecessary. 100% of the cells are living, making it just as potent as fresh yeast, with the added convenience of a longer shelf life.

Adjust your ratios
If you're looking to double a bread recipe, don't double your yeast. More yeast means faster fermentation, which will leave you with too much dough to shape in too little time: when you're shaping your last loaf, your first may already be done with its rise. King Arthur recommends using 2 to 3 teaspoons of yeast for up to 24 cups (roughly 6 pounds) of flour.

When substituting Active Dry yeast for Instant yeast, use 25% more to account for the higher percentage of dead cells in Active Dry. When substituting fresh yeast for Active Dry or Instant, you should roughly double the amount of yeast called for.

Storage: 
When buying large quantities of dried yeast, you'll want to store it in an airtight container (acrylic or glass is best) in the back of your freezer to minimize fluctuations in temperature. Be sure to return it to the freezer immediately after taking what you need. Fresh yeast can also be frozen. If buying large quantities, crumble your yeast into smaller pieces and freeze them in ziplock bags or wrapped tightly in plastic wrap; this way, you'll be able to thaw and use only as much as you need.

Last but not least:
Remember that the more you work with yeast, the more comfortable you'll become. Baking demands that you experience occasional failure; once you accept this, you'll be on your way to a lifelong baking habit.

Ready to get baking? Here are a few recipes to get you started: