Items like yeast, baking soda, and baking powder have an expiry date. As they age, they rise less. After about a year they won’t do their job anymore. If your cookies remain flat or your bread doesn’t rise like it used to, it’s time to toss the old ones.
Buying these ingredients in bulk packages is often a waste of money because they’ll expire before the entire box is used up. I replace all three on the same day to keep things simple.
You can either leave them in their original box and write the date of purchase onto the box, or transfer to a sealed container, and tape the date onto it. After 12 months are up, say goodbye. On the bright side, most stores sell a generic box of each that costs one dollar so it’s not a huge loss.
(The same goes for thickening agents like corn starch powder.)