Yeast is actually a dormant, single-celled fungus that is reactivated when you add warm water. These feed on the sugars in the flour, and produces carbon dioxide and alcohol. The air bubbles help the dough rise, and sets the stage for perfect bread.
Yeast also helps the gluten develop. As you knead the dough, the water and protein molecules bind together. We’ll skip the complicated chemistry lesson, but the air bubbles from the yeast help those molecules move, reconnect, form more gluten, and turn into a smooth and elastic dough.
Fresh, high quality yeast can also help with the bread’s fruity and buttery flavor and aroma—or that all too familiar and comforting scent of bread baking in the oven.
Does yeast expire? Yes, yeast does expire, and “bad” yeast can affect the quality of your bread and pastries. While expired yeast may not make you sick, it can impact results while baking such as having the dough not rise correctly.
That’s why it’s important to know how to store it properly, and how to check its “freshness” before you add it to any of your baking ingredients.
How Long Can Yeast Be Stored?
You can store an unopened box of yeast in a pantry or cabinet for up to two years. Make sure it is cool and not exposed to direct sunlight, and the box is sealed and has a good purchase-by date.
Once you open the box, you need to put it in the refrigerator (use within four months) or freezer (use within six months). Make sure the container is dry and air-tight.
Does Old Yeast Lose its Potency or Efficacy?
Yeast is a living microorganism, so it’s more perishable than other dry ingredients. Even if it doesn’t look expired, it loses it efficacy especially when exposed to heat, moisture or air.
That’s why the conditions in your kitchen or storage area can affect how long you can store yeast. Is it very hot or humid? Is the pantry or cabinet near a window? Did the package become damp while it was sitting in the freezer or refrigerator?
So even if yeast isn’t expired, it doesn’t mean that it is working 100%.
How Can I Check if my Yeast is Still Working?
Professional bakers recommend doing a ‘Yeast Freshness Test’ before adding it to any dough. Make sure your yeast is at room temperature.
- Get a 1-cup liquid measuring cup.
- Add half a cup of warm water. If you have a thermometer, it should read 110° to 115°. If not, just make sure that the water isn’t steaming or hot to the touch – you can comfortably let your finger sit in it for several seconds.
- Dissolve a teaspoon of granulated sugar into the water.
- Add about 2 and ¼ teaspoons (or a ¼ ounce packet) of dry yeast.
- With your watch or timer, observe how long it takes for yeast to active. Within 3 to 4 minutes, it should start to rise. Within 10 minutes, it should be very foamy and have risen to the 1-cup mark.
If your yeast doesn’t activate, takes longer to activate, or doesn’t reach the 1 cup mark, it’s lost its efficacy. Discard it and use a new pack.
If it works perfectly, you’re ready to bake! You can use the yeast water in your recipe, but make sure to measure the amount you really need.
What’s the Best Way to Store Dry Yeast so it Doesn’t Spoil?
You can preserve your yeast’s shelf life by taking these simple precautions.
- Press out any air in the package and fold it down, so any leftover yeast is tightly compressed. Seal the package with tape.
- If you bought a big box, divide the yeast into portions and store in small zipper bags. Remember to press out any air before storing. Write down the date you opened the bag, and a “use by” date (4 months in the refrigerator, 6 months in the freezer).
- If you use yeast often, consider investing in air-tight, vacuum-sealed jars. The pump removes all air, and they’re more reliable than the usual zipper-locked plastic bags.
- If you only bake once in a while, buy yeast in packets. These “single-serve” sachets are usually just enough to make one batch of bread, and can be stored in the pantry until you’re ready to bake.
- Check the yeast’s “best sold by” date. You don’t know how long it’s been sitting on that supermarket shelf! Some people also like to buy their yeast from big supermarkets or bakery supply stores, rather than smaller supermarkets where yeast isn’t a popular item.
What Happens if You Use Expired Yeast?
Expired yeast won’t poison you or make you sick. Unfortunately, your dough might not rise and you won’t get very good bread or pastries!
If you tried an old packet of yeast and realize (too late) that your dough is headed for disaster, you can rescue it by adding a packet of fresh yeast. Just mix the yeast with a little water and sugar, and add to the dough mixture. You may have to add a little more flour to make up for the extra liquid in your recipe.
Can You Substitute Another Ingredient for Expired Yeast?
It’s a baker’s worst nightmare: you realized your yeast has lost its efficacy, and there’s no time to run to the store to get a new box. Can you substitute another ingredient?
You can try:
- Baking powder
- Baking soda mixed with an acid like lemon juice, cream of tartar, buttermilk, or a mixture of milk and vinegar mixed in a 1:1 proportion
- Sourdough starter
Both baking powder and your baking soda-acid mixture have a faster rise time, and they won’t give you exactly the same results as yeast. This may work for heavier or denser breads, but some recipes that yield very light and fluffy breads can only work with yeast.
If you already have sourdough starter in your refrigerator, you can use it as a quick yeast substitute. However, it has a slower rise time than yeast, and it already has a very thick texture. This means you’ll need to adjust your recipe to achieve a good dough consistency.
But hopefully, by properly storing your yeast and doing a yeast test, you won’t be caught in a situation where you’ll need to find last-minute substitutes. Baking often requires precise ingredients and measurements, so switching out yeast for other leavening agents is always a risk.