While cleaning your pantry, you found one or two packets of yeast. On closer inspection, you realized they were old — very old, perhaps even expired.

That sparked a question: How can you tell if the yeast is still good? After all, the last thing you want is waste time, effort, and ingredients on a dough that will never rise.

And so, you did what any prudent home cook in your situation would have done: You pulled out your phone, did a quick search, and landed here. Welcome.

We’ve done our fair share of tests in the kitchen here at Home Cook’s Weekly, and in this story, we’ll show you exactly how to check if a packet of dry yeast is still active.

Testing If Yeast Is Active

Testing a packet of yeast is easy. Here’s my simple, no-fuss method:

Mix your yeast with lukewarm water in a cup or glass, then let it sit for 5 to 10 minutes. If the water turns foamy and bubbly, the yeast is active and will help your bread rise. If not, the yeast is dead, and you’ll need to use a new packet.

This method works for all kinds of yeast — be it fresh yeast, active dry yeast, instant yeast, or bread machine yeast.

Here’s what to expect:

On the left side, a cup with dead yeast; the right side shows a cup with active yeast.

Dead yeast cells simply float in the water without any change. Live yeast cells, on the other hand, start bubbling up and making the mixture foamy, especially in warm conditions.

You don’t need much water — just enough to cover the yeast. Stir a bit to form a thick paste. If your recipe permits it, consider adding ½ teaspoon of sugar (white, brown, cane sugar; the type doesn’t matter). The sugar gives the yeast a quick boost.

It’s very important to use lukewarm water. Water that’s too hot (like fresh from a kettle) or too cold (straight from the fridge) can kill the yeast cells and spoil the test.

Once you’ve confirmed that your yeast is active, simply mix the foamy liquid into your dough and let it do its work.