How baking powder & baking soda work – Chemistry of leavening agents

Ever forgot to add the baking powder or baking soda to your recipe? Or used baking soda and baking powder in your cake, only to discover it resulted in a flat cake?

Baking powder & baking soda have a crucial role in a lot of baked goods: they make your food a lot fluffier and aircoyier. Without them, you may end up with a flat pancake or a solid cake. They’re very similar, but not the same, which at times can be confusing. So how do they really work? And how are the two different? It’s all easy to explain, using a little bit of chemistry and some chemical reactions.

Role of baking powder & baking soda

You add baking powder & baking soda to your food to leaven it, to add air. This is why they are commonly called leavening agents. By adding these leavening agents, your muffin becomes lighter and your pancake fluffier. Leave them out and you end up with a dense product.

Baking powder and baking soda are added for the same reason, but in slightly different situations. Let’s discuss how each of them works first, it will start to clarify how they’re actually different!

How baking soda works

Baking soda is the general name for a component called: sodium bicarbonate (have a look at the ingredient declaration of your baking soda, it will likely say just that or something very similar, in Europe it may conain E500 which is the same again). The chemical formula for sodium bicarbonate is: NaHCO3. This is a salt, containing of two ions: Na+ and HCO3.

When you dissolve baking soda it will split into these two separate ions, both floating around freely. Na+ (the sodium ion) won’t do anything, it will just remain in the water. The bicarbonate (HCO3) on the other hand is quite reactive in water. If acid is present (this can be through lemon juice or yogurt for instance), the bicarbonate will immediately react with it in a so-called acid/base reaction. During this reaction water as well as carbon dioxide (a gas) are formed. It’s this gas that causes a cake to rise up in the oven!

The chemical reaction of baking soda

You can write this chemical reaction down as follows:

HCO3 + H+ H2CO3 –> H2O + CO2

See that part of this reaction is an equilibrium, which means that it can go back and forth (which is very common for acid/base reactions). During the second part of the reaction water (H2O) and carbon dioxide (CO2) are formed. Once these gases are formed the reaction cannot go backwards again as easily, they will evaporate away.

perfect scone dough scones
These scones rely on leavening agents to give them that extra puff up!

How baking powder works

Now let’s have a look at your pack of baking powder. It might say something like: sodium hydrogen carbonate & disodium dihydrogen diphosphate.

‘Sodium hydrogen carbonate’ is actually baking soda, it is the same type of carbonate. As a result, it will react in the same way as we just discussed for baking soda!

What makes baking powder different though, are the other ingredients, in this case a phosphate. Remember how baking soda needs another acid for it to start reacting? For baking soda to work you need to add this acid, however, in baking powder this acid is part of the powder itself. The other component, in this case the disodium dihydrogen diphosphate (chemical formula: Na2H2P2O7) serves as the acid.

Since both the acid and the baking soda are present in a dry form in the baking powder though, they will not yet react in the powder. However, once they are placed into a liquid and heated, they will react! It depends on the exact formulation of the powder whether it needs heat to react fully. In most cases though, the baking powder is formulated in such a way that it will only fully react once heated. This gives you some time to place that cake in the oven without risking it over-expanding!

Chemical reaction of baking powder

It doesn’t necessarily have to be this specific component, but baking powder will always contain an acid of some sort. If you write it down as a chemical reaction that will look like:

NaHCO3 + Na2H2P2O–> Na3HP2O7 + H2O + CO2

The difference between baking powder & baking soda

You should now be able to tell the difference between the two:

  • Baking soda = baking soda only, it needs acid to react
  • Baking powder = baking powder + dry acid

In other words, baking soda is one of the ingredients of baking powder. In both cases it is the baking soda that reacts and creates the gases.

inside of pumpkin cake donut hole
A pumpkin cake donut, uses baking powder to become light and airy on the inside!

A pinch of baking powder history

Baking soda is actually quite a recent invention and truly revolutioned baking. Before baking powder & soda become available cooks still wanted those light and airy cakes. However, this meant either having a lot of patience or a lot of hard muscle work.

The two most common ways to include airiness in your baked goods were yeast & whipping up egg whites. Yeast needs time to create air bubbles though, as you know from baking bread. You need to wait hours (or days when making a sourdough starter) until the batter or dough has become light and airy enough. Nowadays, you can buy dried instant yeast, which makes life a lot easier. Before this was available though, it would take a lot of time and effort to maintain the yeast and ensure it remains alive and fit for the next set of bread baking.

The other option, whipping up egg whites, can give very delicate and light cakes, however, consider the days before electric mixers. It would have taken a lot of effort to whisk up all those eggs.

Therefore, the invention of baking soda truly was revolutionary. It allowed cooks to spend a lot less time on their regular baking. Instead of maintaining their yeast, they could use baking soda to make what we now call a quick bread or soda bread. A whole new range of opportunities for baking cakes opened up as well. All of a sudden light and airy cakes were within reach for most by using baking soda.

Invented in the 19th century

In the 1840’s baking soda was introduced as an aid with baking. However, as we learned earlier, baking soda still needs some acid in the recipe to work. This is why a soda bread often contains buttermilk, you need the sourness to activate the baking soda and have it start creating those bubbles. Nowadays our buttermilk and yogurts are of quite a consistent quality, but at the time, the quality of ingredients was by for not as consistent. This made working with baking soda still somewhat challenging.

In 1856 though, the current baking powder type was invented (and patented) by E.N. Horsford. In his invention he describes exactly which components he mixes together to get a dry form of an acid phosphate (which is the ingredient present in your baking powder). Horsford packaged the two ingredients in the correct ratios, added some corn starch to absorb excessive moisture and started selling it.

Baking powder wars in the US

Baking powder was very hard to manufacture. The phosphates could be mined quite easily and as a result the US had hundreds of baking powder manufacturers. To help (mostly) housewives use baking powder they published cookbooks containing recipes for baked goods made with baking powder. There was some fierce competition during these days. Nowadays though, only a few large baking powder brands are over.

If you’d like to learn more on the topic, listen to an interview with the author of Baking Powder Wars, a great episode on the podcast Taste of the Past.

two stacks of freshly made English muffins
English muffins also relying on baking powder to become light and airy.

Revolutionary for women

In the US especially (and to a certain extent in the UK), the invention of baking powder was literally revolutionary for women. Before, women, who were responsible for baking bread, had to keep and maintain their yeast strains. Now though, they could switch to the way more convenient baking powder, literally freeing up a lot of their time. This caused quite a bit of a revolution.

Baking powder history outside of the US

The history of baking powder outside of the US is way less documented. A likely cause for this is that in Europe most towns still had a lot of communal ovens and bakeries, whereas in the US women would bake more at home. As a result, baking was done to a greater extent by professionals, for whom maintaining the yeast was considerably more manageable, but they were also simply less inclined to change things from the way they were.

Even nowadays, baking powder & baking soda are less common in many European countries (the UK might be an exception) and sold more in smaller portions as opposed to large containers. A common brand in western Europe for these ingredients is Dr Oetker who started selling the products as early as the late 19th century.

For regions outside of Europe and the US several other explanations for a lack of their baking powder history are available. For one thing, a lot of Asian countries rely less on bread as a staple, instead relying more on rice. Others eat more flatbreads, which don’t need any raising agent at all.

spiced muffins with coffee glaze
These muffins have puffed up beautifully, thanks to the baking powder in there!

Using baking powder & baking soda

Now that you know the difference between baking powder and baking soda it will be easier to use them appropriately in your recipe. You know that baking powder already contains acid, whereas baking soda does not.

As a result, the same weight of baking powder contains less active bicarbonate than the same amount of baking soda. 10g of baking soda will literally be 10g of baking soda. 10g of baking powder though will contain acid, corn starch (or something similar) and the bicarbonate. As a result, if you want to replace baking soda for baking powder, you will need to use about 3-4x as much.

Generally speaking, it is easier to replace baking soda with baking powder than the other way around (as long as you correct for those quantities). This is because baking powder is pretty much fool proof. If you want to change the other way around, so replace baking powder with baking soda, you have to make sure the recipe contains enough acid for the baking soda to work. You could do this by replacing milk by butter milk or adding some lemon juice for instance.

Some recipes

We use baking powder and baking soda all throughout this website for a variety of recipes, here’s a selection:

Sources

History Extra, A brief history of baking, August-2018 link

E.N. Horsford, Improved preparation of acid phosphate of lime (patent), 1868, link

B. Panko, The great uprising: how a powder revolutionized baking, 2017, link

Sally’s baking addiction, Baking basics: baking powder vs baking soda, 2015, link

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