Leavening agents can make your food creations airy and light. They will introduce air into your cakes, muffins, pies, candies, etc. How they do this? By producing gas in a chemical reaction. Today we’ll be having a closer look at the science behind these leavening agents, using muffins as an example of how to use them.
Let’s start this analysis of with the recipe. I found this recipe on the blog My name is yeh (with beautiful photos!), it’s originally a recipe for donuts. But, since I don’t have a donuts pan and do have a muffin pan I adjusted the recipe to my flour type and muffin shape :-), here it is.
- 120g sugar
- 275g flour
- ¼ tsp salt - or half of that
- ½ tsp baking powder
- ¼ tsp baking soda
- 1 tbsp spice mix - I used a mix of ginger, cardemon, nutmeg, cinnamon and cloves
- 1 medium egg
- 3 tbsp buttermilk
- 3 tbsp oil - I used sunflower oil
- 40 ml coffee - preferably cooled down to room temperature
- ½ cup icing sugar
- 2 tsp milk
- 2 tsp coffee
- few drops of vanilla
- Mix all the dry ingredients.
- Add all liquid ingredients and whisk through with a whisk, this should be easy to do - thanks to the high sugar content in your dry ingredients.
- Fill a muffin pan with the mixture.
- Place in the oven at 190C for approximately 25 minutes - a tester should come out clean
- Enjoy or coat with a coffee glaze made by mixing the icing sugar, coffee, milk and some vanilla
What are leavening agents?
Leavening agents are ingredients you can add to your baked goods to introduce air bubbles. These air bubbles aerate the product and make it nice and light. Muffins or cakes without leavening agents would be very dense and would miss their airiness. The two most common leavening agents for muffins are baking soda and baking powder. Even though both are very common in recipes, and often they’re even used together, they are not identical.
The difference between baking powder & baking soda
Baking powder is baking soda with some additional ingredients. In other words, baking soda is one of the ingredients of baking powder.
Baking soda is the ‘active component’ in the baking powder. It is the ingredient that forms the air bubbles. However, baking soda requires other ingredients to actually become active. We’ll discuss the details below, but simply said an acid is required to activate the baking soda. It’s this acid that is also part of baking powder (in a dried form).
Before diving into their uses, we’ll do a further deep dive of the workings of baking soda and how it forms those gas bubbles.
pH, acid, base and baking soda
A whole group of chemical reactions that take place in food can be associated with acids and bases. The pH of a liquid is determined by the number of hydrogen ions (H+). The more of those, the more sour a liquid is. The opposite of acidic/sour is alkaline. A very alkaline substance contains a high concentration of hydroxide ions (OH–). Notice that H+ and OH– together form water (H2O)! A neutral solution would be water, in water the two are in balance.
There are a lot of components who will behave differently depending on the pH of a liquid, thus whether there are more or less protons. In acid/base reactions molecules exchange hydrogen ions. One components can lose it whereas the other component can receive.
Remember that water is neutral. When an acid is added to water it will lose a proton, that way it will make the water sour. The concentration of hydrogen ions has increased. In chemistry we would write that down as follows:
HA –> H+ + A–
The other way around, when a base is added to water it will take up a proton from water and increase the concentration of hydroxide ions. That can be represented as follows:
BOH –> OH– + B+
Science of baking soda
Ok, hope that very quick introduction to acids and bases helped. Let’s see how we can apply this in our leavening agents. Baking soda is the general name for a component called: sodium bicarbonate (it even says exactly that on my pack of baking soda), the chemical formula is: NaHCO3. This is a salt, containing of two ions: Na+ and HCO3–. When this dissolves in water the two ions will split. If acid is added to this water, the ion HCO3– will ‘perform’ an acid/base reaction! That will look as follows:
HCO3– + H+ –> H2CO3 –> H2O + CO2
Note, in real this is an equilibrium reaction. The reactions can actually also take place the other way around (from right to left)!
If you’re a little familiar with chemical formulas you might have noticed that in the reaction of sodiumbicarbonate with the acid (the hydrogen ion) water (H2O) and carbon dioxide (CO2) have formed. The last of which is a gas! This gas will leaven the product, exactly as a leavening agent is expected to do!
Science of baking powder
So I hope you got that, now let’s look at baking powder. When I look at my pack of baking powder it says the following: sodium hydrogen carbonate (this is the baking soda, just a slightly different chemical naming), disodium dihydrogen diphosphate and wheat flour.
The wheat flour is easy, that is there to keep the powder dry. It can absorb moisture and improve the flowability of the powder. You will often see some sort of starch in your baking powder. It’s there for stability reasons, doesn’t do anything else.
The other component, disodium dihydrogen diphosphate (chemical formula: Na2H2P2O7) serves as an acid. It doesn’t necessarily have to be this specific component, but baking powder will always contain an acid of some sort. This acid serves to initiate the reaction of baking powder, in this case that will look like:
NaHCO3 + Na2H2P2O7 –> Na3HP2O7 + H2O + CO2
Since both the acid and the baking soda are present in a dry form they will not react in the baking powder. However, once placed into a liquid and heated, they will react. It will depend on the acid whether the reaction will only take place when heated, or also straight after contact with the acid.
Leavening agents in recipes
Now you know that the leavening agent baking soda is actually part of baking powder. You also know that you need an acid with you baking soda to make it form a gas. In recipes you will often see the use of buttermilk, lemon juice or the like. When using baking powder you don’t need the acid, it’s already been put into the baking powder.
Once you know this, you also know that you cannot substitute the two leavening agents. Using the same amount of baking powder as baking soda will give you a lot less of the active sodium bicarbonate molecules and thus less gas formation. It depends on the amount of sodium bicarbonate in your baking powder to know how to convert the two.
Often a combination of the two is used in recipes, as was the case for my muffins. Since the recipe uses buttermilk, this can be used to activate the baking soda. Apparently, not enough buttermilk is present to form the required amount of gas and raise of the muffins. So, baking powder is also added to add that extra raise. Interesting, isn’t it?
Now let me enjoy my leavened muffins, originally donut.
History of baking powder
Interested to learn how baking powder changed the way bread is baked in the US, how it played a role in emancipation of women and why just about every town had their own baking powder brand? Listen to a great episode on the podcast Taste of the Past, in which they interview the author of a book on the history of baking powder.
Baking soda infographic
Looking for a simple visualisation of how baking soda works? Do have a look at this series of infograhics which contains one on baking soda!