The biggest mistake you're making when baking with yeast

Seems like certain ingredients on our pantry shelves are especially prone to falling by the wayside, sitting for months or years untouched, possibly tucked behind some just-in-case cans of corn or barely-used spices. If you were once an aspiring baker who lost interest or never found the time, perhaps one of those forgotten items is yeast.

Want to whip some out to try your hand at baking again? Not so fast — like any food, yeast has a limited shelf life and, unlike many other foods, yeast is actually alive. According to Fox News, "yeast is a microorganism that, when activated with liquid and fed by sugars, creates air bubbles that give bread its rise and texture."

In general, an opened package of active dry or instant yeast will keep for three to four months in the fridge (via The Spruce Eats). Red Star Yeast notes that opened packages should be stored in airtight containers to keep out moisture, air, or heat (freezing the yeast can also extend its life), while unopened packages should be stored in a cool, dry location. But even with optimal storage practices, you can't simply toss in ages-old yeast and expect proper performance.

How to test yeast for freshness

If you're not entirely sure how long that yeast has been sitting around, or if the expiration date has just passed, there is a test you can perform to make sure it's not dead in the water (literally).

Fox News recommends adding an envelope of yeast to 1/2 cup of warm water (make sure it's less than 115 degrees Fahrenheit, as too-hot temperatures can kill the yeast), plus a teaspoon of sweetener, like sugar, honey, or agave syrup, then stir. After five to 10 minutes, a still-active yeast will show bubbling and frothing — that's the sign it's still useful for baking.

If you've bought your yeast recently or the expiration date indicates it's still good to go, some experts say this test isn't 100 percent necessary for active dry yeast and instant yeast varieties; they can simply be added to the recipe as normal (via Epicurious). But when the indicators of freshness are less clear, this simple test will help ensure your baked goods rise as expected.