Baking powder and baking soda- what's the difference? Let's face it, they both look the same, taste the same (please don't taste them, they don't taste so great...kinda salty!), and are both used as chemical leaveners in various baked goods. Yes they may have these things in common, but they're actually pretty different. Let's start with baking soda shall we?
Baking soda, also known as sodium bicarbonate (if you want to get technical) is a salt that decomposes and gives off gas when exposed to moisture, heat, and acid. In order for baking soda to act as a leavener in baked goods, it must be combined with acid. It's this acid that reacts with the baking soda, causing it to break down and give off carbon dioxide gas, which helps to leaven the baked good.
baking soda + acid > carbon dioxide + water + salt
It's important to get the amount of baking soda just right in recipes. Too much will produce a yellow/green discoloration and leave a salty, chemical aftertaste from the salt residue left behind. Too little and there won't be enough to leaven the baked good.
Common acid ingredients used in baking include buttermilk, yogurt, sour cream, fruits and fruit juices, vinegar, syrups such as honey, brown sugar, unsweetened chocolate and natural cocoa powder. All of these will react with baking soda to produce carbon dioxide and help leaven your baked good.
So, what's baking powder then?
Baking powder is actually a combination of substances. It actually contains baking soda, one or more acids (such as cream of tartar), and starch or some other stabilizer to stop the soda and acid reacting. Baking powder also releases carbon dioxide when exposed to moisture and heat, however it doesn't require the presence of an acidic ingredient since it already contains acid. Since baking powder is activated once liquid is added producing carbon dioxide bubbles which help to leaven, it is important to get your cake into the oven as soon as everything has been mixed together. Store your baking powder in a cool dry place, as it can loose it's affectiveness over time if exposed to moisture or heat. Unsure as to whether your baking powder is still good? Add a teaspoon to some water and if it fizzes, you can rest assured that it will still work!
Most baking powder you get these days is known as 'double acting'. Basically what this means is that it reacts twice- once when liquid is added, and again when heat is applied. This helps to give the baked good a longer, slower rise.
What about recipes that call for both baking powder AND baking soda?
It's a simple answer really. Sometimes one leavener just ain't enough! Some recipes don't contain enough acid to react with the baking soda and produce carbon dioxide, and so baking powder is required too. Also, baking powder and baking soda affect colour, flavour, and the tenderness of the finished baked good and so sometimes it's about getting the balance of both leaveners just right!
Can you substitute one for the other?
Well it's possible, but I wouldn't recommend it as you may well need to adjust other ingredients. For example, if you want to substitute baking soda for baking powder, you're going to need around 4x as much and this is likely to affect the final flavour- you may be left with a salty, chemical tasting product, which is not great! On the other hand, if you want to substitute baking powder for baking soda, you're going to need some form of acid in the recipe to get it to react and leaven your baked good. If you're a newbie baker, I would always suggest sticking to the recipe until you have enough background knowledge that you're able to tweak things.
Do you have a baking question of your own? Let me know in the comments below so that I can answer it for you!