How to test yeast, baking powder, and baking soda for freshness

The holidays are coming. You’re on a tight schedule. You want everything coming out of your kitchen to be absolutely perfect.

What’s the first thing you need to do? Test your yeast, baking powder, and baking soda for freshness.

Let’s start with baking soda, which you’ll no doubt be using in all kinds of cookies, gingerbread, muffins, and other holiday treats.

Test yeast, baking powder, and baking soda for freshness via @kingarthurflour

To test baking soda for freshness:

Put 1 tablespoon vinegar in a small bowl.

Test yeast, baking powder, and baking soda for freshness via @kingarthurflour

Stir in 1/2 teaspoon baking soda. The mixture should fizz immediately – and quite vigorously, too.

What’s happening? Chemically speaking, baking soda (sodium bicarbonate) is a base. Vinegar is an acid. Base + acid = reaction.

If the two don’t fizz on contact – or the fizzing is gentle/minimal – it’s time to invest in a new carton of baking soda.

Next up: baking powder, the basis of cakes and cookies of all kinds, to say nothing of biscuits, pancakes, scones, muffins, quick breads… baking powder is our most popular chemical leavener.

Test yeast, baking powder, and baking soda for freshness via @kingarthurflour

To test baking powder for freshness:

Put 2 tablespoons warm water in a bowl.

Test yeast, baking powder, and baking soda for freshness via @kingarthurflour

Stir in 1/2 teaspoon baking powder. While you won’t see quite the vigorous reaction you get from baking soda/vinegar, the mixture should definitely bubble and foam.

What’s happening? Baking powder is a combination of baking soda (base) and cream of tartar (acid), with some cornstarch thrown in to buffer the mixture and prevent an immediate reaction. Since baking powder already includes acid, you don’t need to combine it with acid (vinegar) to see if it’s fresh; you simply need to get it wet.

Why is that? Double-acting baking powder, the kind we all purchase at the supermarket, reacts twice: first when it’s combined with liquid, and again when it hits the heat of the oven. Combining it with liquid in a recipe (e.g., with the milk in a cake recipe) gets the leavening started. And when you put the pan of cake batter into the oven, baking powder offers another burst of leavening power, thanks to the oven’s heat.

Finally, yeast – the friendly fungus that’s loved and feared in equal parts, due both to its sometimes fickle personality, and its enormous influence on your bread-baking.

Since yeast is such an important ingredient, you want to make sure it’s fresh and active. Here in the King Arthur Flour test kitchen we use SAF Red instant yeast on a regular basis; we don’t test its freshness because it comes vacuum packed, we store it in the freezer, and we use it quickly.

But for those of you who are occasional yeast bakers, relying on a three-pack of yeast from the supermarket (or wondering if that instant yeast you stashed in the freezer a year ago is still good) – it’s important that you test your yeast to see if it’s viable.

Test yeast, baking powder, and baking soda for freshness via @kingarthurflour

To test yeast for freshness:

On the left, active dry yeast. On the right, SAF Red instant yeast.

Dissolve 1/2 teaspoon sugar in 1/2 cup warm water.

Test yeast, baking powder, and baking soda for freshness via @kingarthurflour

Stir in a packet of active dry yeast; or 2 teaspoons instant yeast.

Go away. Come back in 10 minutes.

Test yeast, baking powder, and baking soda for freshness via @kingarthurflour

After 10 minutes, the yeast has started to bubble and expand.

Test yeast, baking powder, and baking soda for freshness via @kingarthurflour

Give it another 10 minutes, and it’s domed and very light.

Yes, both of these yeasts are active and ready to go. Add the yeast/water to your recipe, reducing the liquid in your recipe by 1/2 cup.

Test yeast, baking powder, and baking soda for freshness via @kingarthurflour

Just look at those bubbles! This yeast is light as froth, and clearly ready to join you for an afternoon of bread-baking.

Don’t delay – test your leaveners today.

After all – the loaf you save may be your own.

PJ Hamel

PJ Hamel grew up in New England, graduated from Brown University, and was a Maine journalist before joining King Arthur Flour in 1990. PJ bakes and writes from her home on Cape Cod, where she enjoys beach-walking, her husband, two dogs, and really good food!


  1. James Kline

    I read your article with great interest. A bakery we work with uses 1-lb blocks of fresh compressed yeast in their dough. They are looking for a simple testing method to determine if a lot is good or not (they just lost half a day and several doughs due to bad yeast). Could the method you describe for instant and active dry yeast be adapted? I’m trying to find them a solution that doesn’t require a chemist to perform the test.
    Thank you,
    Jim K.

    1. The Baker's Hotline

      Hi James, while we’d love to help, we’re not qualified to ascertain what will or won’t work at the bulk level in a bakery. We encourage you to have one of the folks from the bakery contact our Bakery Flour Sales Support Team — those are the folks who may be able to steer the yeast-testing in the right direction. (Please send an email to bakeryfloursupport[at]kingarthurflour[dot]com for further assistance, using the appropriate symbols at noted.) Kye@KAF

  2. JoAnn Dibeler

    Thanks for the freshness test. I usually just cross my fingers or, as others have said, just toss it and buy new. What I’ve been trying to find out is whether the dry granual machine yeast in a jar should be kept in the fridge. I recently had to replace the bread machine with another one from the thrift shop and no matter what steps I take. I did some pretty stupid things that could have contributed to all of the bread fails. The one I had never gave me any trouble. This last loaf should have come out perfectly but the top of the loaf still collapsed. I’m down to blaming the refrigerated jar of yeast. And where do I find diastatic malt flour?! 3 grocery stores in our town and I can’t even find wheat germ or wheat gluten.

    1. The Baker's Hotline

      Hi JoAnn, we recommend storing yeast in the fridge or freezer to help extend the shelf life — don’t worry, you’re doing the right thing when it comes to storing your yeast. You can always add the yeast to a bit of warm water as shown in the post to ensure it’s not your yeast to blame if the loaf fails. If your loaf is rising beautifully and then sinks, it means that your dough is overproofed or left to rise for too long. Next time, try reducing the amount of yeast you use by about 1/4 teaspoon and also watch the dough more closely. As soon as you can poke it with your finger and it no longer springs back, it’s ready for the oven.

      As for your question about Diastatic Malt Powder, you can order it on our website here. Our brand of this product isn’t sold in grocery stores but exclusively available through our online store. Best of luck with your next loaf! Kye@KAF

  3. jon spats

    I have read on some blogs, when making plzza or bread , that 1/2 teaspone of diastatic malt flour should be added for every 3 cups of flour. But i noticed that KAF has malt flour in it all ready.

    1. The Baker's Hotline

      Jon, in flours that already have malted barley flour added, the diastatic malt powder isn’t really necessary. It can, however, be helpful when using flours (such as whole grain flours) that do not contain malted barley flour. Barb@KAF

  4. Melanie Romero

    I would like to know the amount of acid to use along with 1/4 t. baking soda to substitute for 1 t. baking powder: vinegar, lemon juice, sour cream, yogurt, buttermilk, cocoa, molasses, brown sugar, fruit and fruit juice.

    1. Susan Reid

      Melanie, the way we keep track is to tie the amount of baking soda to the amount of flour in the recipe, in order to know how much to use (many baking soda recipes are badly overleavened). The ratio is 1/4 teaspoon of baking soda for every cup of flour in the recipe, and the presence of an acid ingredient (usually at least a quarter cup). If you’re using a recipe that doesn’t have an acidic ingredient (pumpkin and maple syrup can also go on your list), a tablespoon of vinegar or lemon juice should do it. Susan

  5. Bakeraunt

    Thanks for the tips. I go though yeast, baking powder, and baking soda pretty fast, but it is good to know how to check. The one ingredient that I do not use so much is Cream of Tartar. Is there a way of testing it for viability? I have a jar that I bought before I date marked baking items, so I bought a new jar recently for a recipe that I plan to try. Am I being over cautious, or should the old bottle be thrown out as I am planning to do?

    1. Susan Reid

      Just for fun, put a teaspoon of baking soda in a quarter cup of water. Stir in a teaspoon of the Cream of Tartar (it’s an acid). If it bubbles, you’re good to go. Susan

  6. annette

    Thank you, after 40 plus years of baking this will cut out a lot of guess work and waste. Light bulb moment: How about printing these tips on a King Arthur Flour bookmarker? Great gift for fellow and future bakers. Give me the first dozen and sell the rest for this idea? ama

  7. Samsnona

    Thank you, after at least 60 years if baking, other than checking yeastI never knew this! I’ve actually bought new baking soda and baking powder just to ensure I “saved my loaf.”

  8. Susan Kline

    Thank you so much for these tips on leavening agents. For years, I have purchased new containers of baking soda and baking powder before the winter holidays. Unused baking soda can always be used for cleaning, but I threw away baking powder. Thanks to you, I now know how to test them!


Post a comment

Your email address will not be published. Required fields are marked *