Does baking soda expire?
There's a "best by" date on my baking soda. I made a honey cake yesterday and it fell after it came out of the oven. Now it has a giant trench in the middle. IIRC, this happened last September, too. I had double checked the "best by" date on the baking powder yesterday when I was baking and that was fine, but somehow never looked at the baking soda. The recipe called for both.
I just looked now. The best by date was, ummm, July 2009.
DH thinks baking soda doesn't really expire because there's nothing to expire and they're just legally required to put some sort of date on it and it's probably not the problem with the cakes.
So, toss the baking soda and figure the cake will work better next year or go looking for another culprit?
If, as your post seems to state, the cake rose normally and then deflated afterward, your DH is most likely correct and both the leavening agents probably are OK.
If there was inadequate rise in the oven, I concur with Val- baking powder is more likely to be the culprit.
Here's a snippet from my kitchen tips file; part of it repeats what Val has already posted...
How to Tell if Baking Soda has Expired
Commercial baking soda and baking powder will last for quite a long time on your cupboard shelf, but they will eventually (over several years) lose their potency and expire. If you're wondering if yours is still good, it's best find out with a quick test before baking rather when your muffins emerge from the oven dense and flat. Here's how!
For baking powder, all you have to do is stir about 1/4 teaspoon of powder into 1/2 cup or so of very hot water. Tap water is fine, and the proportions aren't fussy. The soda will immediately start to bubble if it's still good.
Baking soda needs an acid to get a reaction, so use the same method as for baking powder but add 1/4 teaspoon of vinegar to the water before water before adding the soda. As before, if it bubbles up, your soda is fine to use.
If you don't see bubbles, then sadly, you'll need to take a trip to the store and buy a fresh box! If there isn't much fizzing, your ingredients are likely on their way out. You can probably still use them to get some lift, but your baked goods will be more dense that usual. Don't be tempted to double the amount of baking soda or powder - that would make your food taste seriously strange!
To be honest, I worry more about my baking POWDER than the soda losing effectiveness and usually test out a spoonful in a glass of warm water to see if it bubbles or not and pretty much buy a new can of it each fall (I don't do very much baking but of course, once our first cold front comes thru here in SWFL, I'm a busy and happy baking bee in the kitchen)....Does your recipe include baking powder too by chance?
IMHO, it does expire and/or lose it's effectiveness. Think about other uses - i.e. use in your refrigerator. It absorbs odors, etc. and needs to be changed out occasionally. In essence it can do the same over time sitting in your cupboard depending on it's access to odors and air (do you seal it in a plastic bag and put it on the shelf? Again, this is just my opinion.
There are opinions pro and con re the deodorizing ability in the refrigerator. I recall the equipment expert on America's Test Kitchen saying recently that it doesn't work because there's not enough air circulation in the compartment. It certainly does work as a water softener for laundry or other cleaning, removes stains on surfaces when used as a paste, can be used as toothpaste, loosens burnt-on food when added to boiling water, and can be poured down the drain (where it may or may not accomplish any deodorizing/cleaning).
Martha Stewart suggests replacing baking powder and soda annually, using New Year's Day as an easy-to-remember date. I think I'd choose LABOR Day, since people bake a lot at the end of the year. You don't want tired leavenings
adding to the WORK - another memory trick.