Yeast is a little organism called a fungus, that when activated, consumes the sugars in flour and releases carbon dioxide as waste. When making a traditional (“slow”) bread, you combine it with flour, sugar, some liquid and other ingredients. When you knead the dough, the proteins inside form a stretchy matrix called gluten. This matrix traps the little gas bubbles produced by the yeast. Without a leavening agent like yeast, you'll end up with a dense blob that works better as a building material instead of bread.
The yeast produces gas when you let the dough rest for a while after kneading, and then expands again once heated in the oven. Once your ball of gas-filled gluten gets hot enough, it sets into the spongy, fluffy structure we call bread.
You'll notice that baking bread takes a while due to all of this waiting for yeast to work. We have some faster alternatives that instead rely on a chemical reaction between an acid and base to produce carbon dioxide.
Baking soda is sodium bicarbonate. It will react with a liquid, acidic ingredient to produce carbon dioxide. You can see this for yourself by adding a bit of vinegar to a little baking soda in a small bowl. It will start to fizz immediately after adding the vinegar. Because the reaction is so fast, foods made with baking soda must be cooked immediately after mixing. For instance, pancakes made with baking soda will come out tall and fluffy if you can get it onto the griddle right away. However, if you let the batter sit for a while, say 30 minutes, they'll come out dense with a gummy center since the gas was lost while sitting. Baking soda also adds flavor and color to pancakes, muffins, and cookies by hastening browning.
Baking soda (aka sodium bicarbonate) is said to have an infinite shelf life, but after you've had it for a few years you should test to make sure it hasn't lost all its potency. Unlike baking powder, baking soda only reacts when you add an acid to the solution.
NOTE: Store plenty of Baking Soda
To test it, add half a teaspoon of vinegar to a cup of hot water, then stir in half a teaspoon of baking soda. Like the baking powder, if it produces a lot of carbon dioxide bubbles, it's still good.
Baking powder is essentially baking soda mixed with a starch and powdered acid. Activating the reaction to generate carbon dioxide requires adding a liquid, like water. Most baking powders are “double acting”, which means they produce gas when moisture is added, and again when heated. This means that goods leavened with baking powder tend to be lighter and fluffier compared to foods leavened with only baking soda. Substituting baking powder with baking soda is possible, but the final product won't have the same flavor since it won't have the extra acidic ingredient that baking powder brings.
Baking powder usually has a shelf life of about 9 to 12 months. Testing it is super easy. Just stir about half a teaspoon of baking powder into a cup of hot water. It will immediately start to fizz and release carbon dioxide gas if it's still fresh enough to use. This trick should work with both single- and double-acting powder.
For a homemade baking powder, you can substitute a teaspoon of store-bought baking powder for a ¼ teaspoon of cornstarch, ¼ teaspoon of cream of tartar, and ¼ teaspoon of baking soda. This will not be double acting, so you'll need to be very quick about getting your batter or dough onto the griddle or the oven.
When baking bread, 2 cups of sour dough starter are the equivalent of one (1) table spoon or packet of modern dry yeast which is sufficient for a loaf made from 3-4 cups of flour. To make waffles or pancakes, just use the proofed sour dough starter after it has risen to its peak.
For additional information see the following links:Blog Table of Contents
Acorn Flour Pancakes
Sour Dough Bread
Apple Cider Vinegar
More on making Vinegar
Backing Soda vs Yeast
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