Thursday, November 12, 2015

The Science Behind... Raspberry Breakfast Cake

Welcome to my second post of the "The Science Behind..." series!

If you haven't read it yet, please CHECK OUT the recipe for Raspberry Breakfast Cake, then come back here for the science.

This post will touch on the following topics:

1. How is baking with baking powder/baking soda different from baking with yeast?
2. How come I can substitute the yogurt with sour cream or buttermilk and get the same result?  What else can I substitute out from the recipe?
3. What gives this bread its cakey texture?
4. What gives quick breads their structure?
5. Quick breads often have you separate wet and dry ingredients and then combine them at the last moment.  Why is that?

That's a lot to cover.  So let's get started!

1. What is the difference between baking with yeast and baking with baking soda or baking powder?

Baking soda, baking powder and yeast all achieve the same end result: they help rise the dough or batter by releasing gas.  How they do this, however, is really different.

Yeast is an organism that lives and reproduces from eating the sugar in flour (or any added sugar you use).  As it eats, it releases carbon dioxide gas which builds up inside your dough over time.  Then, when bread is baked in the oven, the heat causes the yeast to release more gas a second time.  This reaction can take place over many hours.  If you try to bake a loaf of bread without letting the yeast gases form, your loaf will be very dense and not taste very good.

Baking soda is sodium bicarbonate.  When mixed with an acidic liquid, it too forms carbon dioxide gas.  Unlike yeast which takes time to release gas, the chemical reaction between baking soda and acid is immediate and so the batter must be baked right away.  For this reason, breads that use baking soda or baking powder are called quick breads.  Yes, this raspberry cake is actually a quick bread!

Baking powder is baking soda mixed with a starch (typically cornstarch) and a powdered acid (typically cream of tartar).  That means you don't need to add a separate acidic liquid to start the chemical reaction - any will do.  Because baking powder also has starch and powdered acid, you typically add more of it to a recipe than baking soda, about three times more.  So a recipe that uses baking powder and baking soda together might say 1 1/2 teaspoons baking powder, 1/2 teaspoon baking soda.

2. How come I can substitute the yogurt with sour cream or buttermilk and get the same result?  What else can I substitute out from the recipe?

Once you have a handle on the reasoning behind baking powder and baking soda, the sky is the limit! Any acidic dairy liquid will have the same effect as the yogurt.  For example:
the recipe for this cake called for sour cream, but I used crema
buttermilk is just milk or cream with a little vinegar

in the case of beer bread, the carbon dioxide in the beer is the leavening ingredient!  Like baking powder and baking soda, the chemical reaction takes place immediately so you need to bake beer bread quickly. 
I also adapted my pancake recipe from one that used milk to one that also included sour cream by adding 1/2 teaspoon of baking soda to offset the additional acid in my new recipe.

Other things you can substitute in the recipe without interfering with the chemical reaction of the leavening agents are: the seasonings (cinnamon would be a good addition), the extract (I throw in vanilla but Niequist calls for almond extract), the berries you choose to use, and the type of sweetener you use.  Because almost no gluten formation takes place, you don't have to worry about hydration levels.

lemon zest
3. What gives this bread its cakey texture?

You may have already guessed why this bread (and all quick breads) have a cakey texture; it's because the gluten doesn't have time to develop if you have to mix and cook it right away.  Also, quick breads tend to have very wet, runny batters (sometimes called "pour batters") which provides lots of room for small air bubbles to form.

4. So if gluten doesn't get a chance to form, what provides the structure for this bread?

The eggs!  If you remember from the last "The Science Behind...," eggs contain both fat and protein.  Protein is mostly found in egg whites, and like gluten strands in flour, it traps the carbon dioxide released by the baking powder or by the baking soda + acidic liquid.

5. Quick breads often have you separate wet and dry ingredients and then combine them at the last moment.  Why is that?

Again, because the chemical reaction between the baking powder or baking soda and the acidic liquid takes place the minute they are combined, recipes often instruct the cook to combine all the wet ingredients together, then all the dry ingredients together before combining the wet and dry into the final batter.  This isn't always necessary, but with two Little Bread Offspring, I find it is a lifesaver.  Often I will mix up the dry ingredients, then I can walk away and do something else knowing nothing chemically will happen while I'm gone.

That's about it for this episode of The Science Behind.  If you want to learn more about baking with baking soda and baking powder, this tutorial from King Arthur Flour is really good.

And now you know a bit more about your Raspberry Breakfast Cake!

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