Iron chef Michael Symon has a show - Cook like an Iron Chef. He says 'if you learn a recipe, you know how to make a dish. If you learn a technique, you can make any number of your own recipes' (I don't remember his exact words but pretty much means the same). I believe that it is one of the greatest advice anyone can give to someone who is passionate about cooking or baking.
As I repeatedly say 'Baking is a science more than it being an art', if you learn the chemistry behind baking, you can convert any recipe to suit your pantry ingredients and make it your own.
There is a common thing that happens in baking. The dough or the batter or the pastry rises when baked. The type of leavening agent used is different in many baked goods and the way they react is different too. In yeast breads, yeast is the leavening agent. When mixed with water and food (flour and sugar), they breathe and release carbon dioxide. They are the reason for the air pockets or holes in the bread.
In quick breads, muffins, cakes, scones, cookies it is either baking powder or baking soda or a combination of these two used to create the same air pockets or to raise the dough. The only baked good that doesn't necessarily need a leavening agent is the pie crust. In that, the cold fat is left without blending it too fine which when heated leaves out the air to make flaky pastry.
Since the title of the post is about baking soda and baking powder, let's see what they are and how they work and why they are used where they are used.
Baking Soda is pure Sodium bicarbonate or Sodium Hydrogen Carbonate (NaHCO3). This powder, when mixed with acidic liquid ingredients, releases carbon dioxide which is nothing but gas. These gas pockets get trapped as holes in the baked goods. At a certain temperature, baking soda looses its properties so that it doesn't keep on releasing carbon dioxide. So, if you bake a muffin and after it rises to full extent, it stops rising further even when it is not cooked completely.
So, what else should be present in the recipe for this baking soda to work? Buttermilk, honey, molasses, coffee, vinegar, fruit juices, any citrus juice, chocolate (natural not dutch processed), yogurt, sour cream. If you don't have any of these acidic ingredients in the recipe, then baking soda will not work. Also, baking soda when mixed with liquid ingredient immediately releases the carbon dioxide. It will not work if you let the batter or dough sit for a while and then bake. End product will be extremely dense, heavy and gummy.
How to check if the baking soda is still good to use:
Mix 1/4 tsp of baking soda with 2 tsp of vinegar. It should frizz immediately. If not, it is too old and have lost its property.
Baking Powder is also a leavening agent which does not need any acidic ingredient in the recipe to work. This starts working the moment it comes in contact with moisture or liquid. That is because baking powder is a mixture of baking soda, an acid usually cream of tartar and corn starch. Corn starch acts like a drying agent and prevents the baking soda and cream of tartar to act together before it comes in contact with liquid. They are mixed in the ratio 1 part baking soda + 2 parts cream of tartar + 1 part of corn starch.
I know what you are thinking - what is cream of tartar? It is the salt that is produced by processing the deposit in the wine barrels where grape juice is fermented and wine is made. So, this is highly acidic. Since baking powder does not need any acidic ingredient in the recipe, it pretty much works very well with any of the ingredient. Then why not use baking powder every where? Answer is to balance the entire equation.
Now, I didn't major in chemistry. But, I do know that if you use too much of a leavening agent, the baked good will not rise. Reason being too big air pockets which combine together and there is nothing to separate them from each other. This causes batter or dough sticking together and that is the reason for no rising.
Commercially available baking powder is double acting. That means, it rises when it comes in contact with liquid and it rises when heated. That is the reason many baked dough or batter that has baking powder can be refrigerated and baked later. They will still work.
How to check if baking powder is good to use:
Add 1 tsp of baking powder to 1/2 cup of warm water. It should frizz immediately. If not, it is no good.
You probably can get all these information on different websites. It is no big deal. I just summarized it here. There is one more thing that we need to understand. That is,
How much to use?
For every cup of flour, you need 1 - 1 1/4 tsp of baking powder.
If you are using baking soda, you need 1/4 tsp of baking soda for every cup of flour.
Why is it used in combination in some recipes?
When used in combination, it has the effect of enhancing the color of the final product. It browns better. More baking soda, browner the end product. Best example for this is pancake recipe. You use baking powder for double acting rising and baking soda for browning the pancakes.
How to adjust the recipe?
Interchanging these two is not as easy as it seems. Because of the complexity of the ph balance that each produces, the end product might taste differently and have a different texture.
Let's take an example of a recipe that you are adjusting as per your pantry.
This is a basic muffin recipe - 1 3/4 cup flour, 1/4 cup sugar, 2 1/2 tsp baking powder, 1/4 salt, 1 egg, 3/4 cup milk, 1/3 cup oil.
To make the same without using baking powder but using baking soda, I would change the recipe like this - 1 3/4 cup flour, 1/4 cup sugar, 1/2 tsp baking soda, 1/4 salt, 1 egg, 3/4 cup butter milk, 1/3 cup oil. Pretty much same results can be achieved.
Now, let's change it to chocolate muffin. I would go like this - 1 1/4 cup flour, 1/2 cup natural cocoa, 1/4 cup sugar, 1/2 tsp baking soda, 1/4 salt, 1 egg, 3/4 cup milk, 1/3 cup oil.
Now, let's change it to chocolate muffin with dutch processed cocoa. I would do this - 1 1/4 cup flour, 1/2 cup dutch processed cocoa, 1/4 cup sugar, 2 1/2 tsp baking powder, 1/4 salt, 1 egg, 3/4 cup milk, 1/3 cup oil.
Same with baking soda would've to be changed like - 1 1/4 cup flour, 1/2 cup dutch processed cocoa, 1/4 cup sugar, 1/2 tsp baking soda, 1/4 salt, 1 egg, 3/4 cup butter milk, 1/3 cup oil.
See, how a simple ingredient substitution can be made to get the same effect?
At the same time, let's say you have a recipe that uses milk and baking powder and there are no other acidic ingredients in the recipe. But, you want to use up the opened carton of buttermilk in the refrigerator. If you use buttermilk instead of milk, adjust the baking powder. Use half of the baking powder and add enough baking soda for half of the flour called for in the recipe.
Say 2 cups flour + 2 tsp baking powder + 1 cup milk will become 2 cups flour + 1 tsp baking powder + 1/4 tsp baking soda + 1/2 cup milk + 1/2 cup buttermilk.
End product might have a different texture, but is worth trying if you are working on a recipe to use other ingredient than what is specified in the recipe.
I hope you got an idea of how these two work. Have you? I would love to know.