Baking is an art as well as a science. One of the interesting and unique aspects of baking bread is that it requires a live and active leavener; yeast. Professional bakers often use yeast in mixtures known as bread starters in order to create a consistent, reliable taste and texture. Whether you are a professional or a home baker just starting out, brush up on your knowledge of yeasts, bread starters, and the scientific action behind baking bread.
Yeast is a living and active organism, unlike the chemical leaveners like baking soda used in cakes and muffins. Yeast is a single-celled organism that reproduces and multiplies rapidly when exposed to moisture and warmth. It thrives on sugars or starches, and when it feeds on these components it produces alcohol and carbon dioxide as by-products. The elastic gluten in bread dough traps the carbon dioxide bubbles that form, allowing the dough to expand and develop a fluffy, airy texture as it rises.
Choosing the Right Yeast
There are a several different types of baker’s yeast. The following are three of the most popular choices among home bakers, including dry active yeast and fast-rising active dry yeast.
Active dry yeast.
For the home baker, single-use packets of active dry yeast are often the best bet, although the yeast usually also available in bulk bags. Professional bakers usually use bulk baker’s yeast, or a bread starter. Active dry yeast is the most reliable and probably the most common type of yeast for the home baker. Store it in an airtight container in a cool, dry place. If left in the open, yeast is more susceptible to moisture and can become active, going bad before it is even used to make bread.
Fast-rising active dry yeast.
This type of yeast is relatively new on the market and boasts rising times that are half that of conventional dry active yeast. Experts suggest mixing this yeast with dry ingredients first, before adding the liquid.
Compressed fresh yeast.
Rarely found in the United States, this kind of yeast has a much higher moisture content, up to 70 percent. It must be refrigerated to stay fresh, and even then it is only usable for two weeks. Store it in the freezer and it will stay fresh up to six months.
Bread Starters Defined
A bread starter is just what it sounds like: a mixture of water and flour that has been colonized by yeast and other friendly bacteria to provide a starting point for new batches of bread. A bread starter is also called a sponge, a mother dough or a pâte fermentée, which means pre-ferment. Starters begin with just a mixture of flour and water. Bakers either add active dry yeast, or allow the mixture to collect naturally occurring wild yeast and bacteria from the environment.
Bakers must “feed” their bread starters in order to keep them alive. Every day or week, depending on the starter, bakers periodically discard part of the mixture and add fresh flour and warm water. The discarded part is combined with bread dough ingredients and is used for baking bread. Or, it can simply be thrown away. Bakers can maintain bread starters for years, even centuries, to create reliable flavor and texture each time they make bread with it.
The Process of Fermentation
Fermentation is just another word to describe the process in which the yeast is activated. For bread starters, fermentation . Fermentation is a process that involves more intense yeast and bacterial action in order to bring a more developed texture and complex flavor to the resulting bread. Starters are usually allowed to ferment and grow for up to three days before they are combined with the dough ingredients. Other starters last much longer when properly fed. Long fermentation periods lend special flavors or textures, and bakers usually employ starters in order to get a unique tasting bread. The type of yeast and the type of flour may differ from starter to starter and is usually dependent on the bread recipe. For instance, ciabatta has a different starter than rye bread.
Choosing the Right Bread Starters
A starter is also called a sponge, a mother dough or a pâte fermentée, which simply means pre-ferment. Allowing the yeast a longer fermentation period produces a different taste and texture in the resulting bread. Below are some of the common bread starters that professional bakers use in their breads.
Biga is a term for a type of starter made with dry active baker’s yeast and used primarily in Italian baking. Ciabatta and Foccacia, popular Italian breads, are made using biga starters. Biga is known for helping create bread with a light texture and lots of airy holes. Biga starters are dry and thick compared to other starters, usually made with more flour than water. Most professional bakers use the Baker’s Percentage to make their starters. For example, a biga recipe might call for a ratio of 100% flour to 60% water, so a baker would mix 10 pounds of flour with six pounds of water to create what is known as 60% hydration.
Poolish is the term for the type of starter most often used in French baking. Like biga, poolish is also made using a dry active baker’s yeast, but the starter is made much wetter than a biga. A poolish is usually made with a one-to-one ratio of flour and water, so 100% flour and 100% water, according to the baker’s percentage. Its origins are Polish, and it was first used in the mid 1800s.
Sourdough starters have been used for centuries to provide tried and true results. This type of starter is made from wild yeasts that occur naturally in the environment, such as lactobacillus and acetobacteria, which take up residence in a batter of flour and water. These yeasts are slightly more microbiologically complex than the dry active yeasts in Biga and Poolish starters. Sourdough starters, unlike others, are often maintained in stable colonies for long periods of time, even centuries, since it is simpler to maintain this type of starter than to remake it. As long as the starter is properly fed and cared for, it can be kept active for years to provide predictable results over and over again.
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