How To Tell If Your Baking Soda Has Expired
Baking soda and baking powder are pantry staples. You can easily buy a box of each just like salt and sugar without any real worry of them expiring before you can use all of it. But that's until you use baking soda to bake a cake and it comes out looking wonky and nowhere near as soft and airy as it should be. It doesn't help that you can't tell expired baking soda by simply its look or smell, as you would with fresh produce or dairy products.
The Spruce Eats suggests that baking soda doesn't go out of date per se, despite the expiration date written on the box. However, baking soda's effectiveness will certainly decline over time. In general, an unopened box of baking soda should be fine to use for two years, but an opened box will only work for about six months. That being said, the website says that consuming expired baking soda is not necessarily harmful to you, but it definitely won't act as a leavening agent in your bakes.
You need acid to test your baking soda
Baking soda works by reacting with an acid to produce bubbles of carbon dioxide gas which is what causes bakes to rise (via The Spruce Eats). To check its potency, add a splash of an acidic ingredient like vinegar or lemon juice to a spoon of baking soda in a bowl. If the mixture fizzes, the baking soda is still good to use and if it doesn't, it has gone bad. If you were counting on it for a recipe, you can swap the baking soda for baking powder (via Sally's Baking Addiction). However, beware that you will need four times the amount of baking powder, and using so much of it can add an unpleasant bitterness.
As for the expired baking soda? Just because it isn't suitable for baking anymore doesn't mean that you need to toss it in the trash. You may not be able to incorporate it into your recipes, but there are plenty of uses for baking soda in the kitchen. Kitchn says that baking soda is an excellent abrasive cleaning tool, even when it's expired. A paste of baking soda and water will easily get rid of stubborn grease stains in the oven, a soak will remove burn marks from cookware, and rubbing it around your sink will get rid of grease and deodorize. So even if your baking soda is rendered useless for a cake, you can at least put it to work around the house.