Chemistry of leavening agents & Muffins

Ever made a muffin without any baking powder or baking soda (=leavening agents)? Or had that one time where you simply forgot to add them and only noticed when they came out of the oven? You will have probably seen that the product turned out completely different without them in there. Leavening agents can make your food creations airy and light. They will introduce air into your cakes, muffins, pies, candies, etc. And without them, you foods can become thick, hard blocks.

These leavening agents introduce the air by producing gas during the baking process. This gas is formed through a chemical reaction. Both baking powder and baking soda use a very similar chemical reaction to do so, however, they operate in a slightly different way.

What are leavening agents?

Leavening agents are ingredients which are added to your baked goods to introduce air bubbles, to ‘leaven’ them. 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 in baking 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.

A pinch of baking powder history

Baking powder is actually quite a recent invention and truly revolutioned baking in the US. Whereas before yeast had to be cultivated and kept, (mostly) women could now use ready to use baking powder. This caused quite a bit of a revolution, helping along emancipation even! What’s more, at the time of introduction, almost every town has their own baking powder brand (if not more than one). If you’d like to learn more on the topic, listen to an interview with the author of a book on the topic, great episode on the podcast Taste of the Past.

The difference between baking powder & baking soda

Both baking powder and baking soda can leaven muffins, however, they are slightly different. Baking powder contains, amongst other ingredients, baking soda. In other words, baking soda is one of the ingredients of baking powder. It’s the baking soda which is the active ingredient that causes the muffin to aerate by producing gases.

Baking soda makes these gases through a chemical reaction which we’ll discuss further on. Apart from enough moisture and heat baking soda requires the presence of an acid (e.g. lemon juice or buttermilk) to perform this chemical reaction.

One of those additional ingredients of baking powder is this acid. This acid is also added in drier, powder form. In other words, baking powder can do its job once enough moisture and heat are present whereas baking soda will always require the addition of an acid.

Science of baking soda

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 + Na2H2P2O–> 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.

spiced muffins with coffee glaze

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?

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.


Chemistry of leavening agents & Muffins

  • Author: Science Chef
  • Prep Time: 10 mins
  • Cook Time: 25 mins
  • Total Time: 35 mins
  • Yield: 6 muffins 1x




  • 120g sugar
  • 275g flour
  • 1/4 tsp salt – or half of that
  • 1/2 tsp baking powder
  • 1/4 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


  • 1/2 cup icing sugar
  • 2 tsp milk
  • 2 tsp coffee
  • few drops of vanilla


  1. Mix all the dry ingredients.
  2. 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.
  3. Fill a muffin pan with the mixture.
  4. Place in the oven at 190C for approximately 25 minutes – a tester should come out clean
  5. Enjoy or coat with a coffee glaze made by mixing the icing sugar, coffee, milk and some vanilla

Now let me enjoy my leavened muffins, originally donut.


Baking soda infographic

Looking for a simple visualisation of how baking soda works? Do have a look at this series of infographics which contains one on baking soda!

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