What Temperature Kills Yeast - Bob's Red Mill Blog
What Temperature Kills Yeast
Baking 101, Learning Center on February 21, 2018 by

What Temperature Kills Yeast

Making bread is an art. Or perhaps a science. In any case, with breadmaking, there are two kinds of leaveners typically used in the baking process. One is baking soda or powder, and the other is yeast.

Yeast is a live fungal organism made of a single cell. Yeast has over 160 different species that live in us and all around us. The type of yeast that is used when making bread is usually the kind that comes in little paper packets. It looks like beige colored granules that essentially lie dormant until they come into contact with warm water at just the right temperatures.

When the warm water hits the yeast, it reactivates it and “wakes it up.” Then it begins to eat and multiply. The yeast organism feeds on the simple sugars found in flour. As they feed, they release chemicals and gases like carbon dioxide and ethanol, along with energy and flavor molecules.

 

Fermentation

This is part of the process used to give bread its rise, and it is sometimes referred to as the fermentation process. As the carbon dioxide gas expands, the bread dough rises. This process of rising happens a lot slower though with yeast than it does with baking powder or baking soda used as the leavening agent. Yeast is also what imbues the bread with all of its yummy flavors and smells.

Some professional bakers believe that carbon dioxide is the sole rising agent, while ethanol is the sole flavoring agent, but it's not entirely so black and white. Ethanol is formed in equal parts to the carbon dioxide, so ethanol also contributes to the fermentation process every bit as much as carbon dioxide does.

 

Gluten Structure

Not only does the yeast help produce carbon dioxide and ethanol, it also assists in the development of gluten. Gluten is the substance that traps gas bubbles and gives the dough its structure. With no-knead recipes, this process is even more important, because as these gas bubbles move around inside the dough, it helps to push and rearrange the proteins into the necessary structure without any kneading required.

The short story is that without yeast, your bread won't rise properly, and you won't get the same look or flavor that you would when yeast is used.

 

Proofing the Yeast

How do you prepare the yeast to be mixed into your next batch of dough? This process is sometimes referred to as proofing the yeast. It is when you add yeast to water, then feed it sugar and stir it together. As the yeast sits in the water, it begins to dissolve and the yeast is activated. Once the yeast has been activated or “awakened,” it will begin to feed on the sugar in the water.

The next step when proofing yeast is to let the yeast mixture sit for several minutes. A good benchmark is to allow 2 to 3 minutes for it to completely dissolve, and then an additional 2 or 3 minutes for the yeast to start growing and show signs of life.

Signs of lively yeast include little surface bubbles on the top of the water. Depending on the variety of yeast, sometimes the mixture may expand even more than you expect!

If you do all of these steps and find that nothing is happening and you are sure you kept your water at an appropriate temperature, then it could be a sign that you need a new batch of yeast, as the batch you’re trying to use may be too old.

Yeast that is older and doesn’t respond to the proofing process is sometimes referred to as “tired” yeast. The reasoning behind the whole method of proofing your yeast is so that you can prove the yeast is viable and ready to do its job before you mix it into your bread dough.

Once your yeast has been proved, the next step is to begin stirring in your flour and salt. Be careful that you stir in the flour first as a bit of a buffer, because yeast organisms don’t like salt. If you pour the salt in first, then your yeast organisms will not be happy campers!

The Magic Temperature for Yeast Growth

At what temperature can you see the best results when proofing your yeast? Good question. Yeast is a finicky little single-celled organism.

Dry Yeast

With dry yeast, if your water is too cold, the yeast will not activate. Or, if they do wake up, they might release a substance that hinders the formation of gluten. Then again, if your water is too hot, you will kill the little buggers and they will be useless.

Typically, hot water somewhere in the range of 105° and 115°F is ideal for proofing dry yeast. 95°F is often recommended for live yeast, but it may not be hot enough at 95°F for activating the dry yeast.

At this temperature, once you pour it into the bowl and dissolve the sugar, it will cool a little bit and be the perfect temperature range for dissolving and activating your bread risers.

Not sure if your water is the right temp? One way to test this is to do the wrist test. Drizzle a few drops of your water onto the inside of your wrist. If it is warm and comfy for you, then it will no doubt be warm and comfy for your yeast too. However, if it is not warm and instead feels hot, it most likely will be too hot for your yeast to survive. By the same token, if it is too cold, then your yeast will simply remain dormant.

Fresh, Live Yeast

If you’re using fresh yeast, then you can shoot for temperatures that range between 95° and 100°F for the proofing process. This is because fresh yeast (sometimes called cake yeast), doesn't need to be dissolved in the water. It simply needs to be combined with water, and when it is combined, it will start feeding and growing right away.

Too Hot to Survive

Regardless of the type of yeast you use, if your water reaches temperatures of 120°F or more, the yeast will begin to die off. Once water temps reach 140°F or higher, that is the point where the yeast will be completely killed off. If you’re doing the wrist test, 120°F feels pretty hot, whereas 140°F feels extremely hot. If you don't trust the wrist test, you can always use a candy thermometer to test the temperatures and get a more accurate reading that way.

The High Heat Caveat

Is there ever a time you can use higher water temperatures? Yes, but only when you are using instant yeast.

Instant Yeast

Instant yeast, sometimes referred to as rapid rise yeast, doesn’t require proofing with warm water before using it. This type of yeast is mixed with flour first, instead of water right away, so the temperatures that are suggested are much higher and can range from 120° to 130°F.

Keep in mind that even though this type of yeast doesn't require proofing, you can proof it if you suspect it might not be lively. You would simply proof it the same way you would proof the active dry yeast. Also, since flour is usually around room temperature, this could be the reason higher temperatures are tolerated.

Rough Temperature Recommendations

The guide below will give you a rough idea of ideal water temperatures for proving your yeast.

  •      Water at -4°F means your yeast will be unable to ferment.
  •      Water at 68° to 104°F means that your yeast’s ability to grow will be hindered, and its growth rate will be reduced.
  •      Water at 68° to 81°F are probably the most favorable range for the yeast to grow and multiply in.
  •      Water at 79°F are considered the optimum temperature for achieving yeast multiplication.
  •      Water at 81° to 100°F is the optimum temperature range for the fermentation process.
  •      Water at 95°F is the fermentation temperature that yields the best result.
  •      Water at 140°F or higher is the kill zone for yeast. At temps like this or higher, you will have no viable live yeast left.

Of course, these tentative estimations can be higher or lower depending on the type of yeast you are using, and whether it is active dry yeast, live yeast, or rapid rise yeast. The bottom line is that yeast thrives in warm water, sleep in cold water, and die in hot water. So, like Goldilocks and the Three Bears, it’s important to get the temperatures “just right” for your yeast to thrive and your bread to obtain the best rise and flavors possible.


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24 Comments

  1. Tom Cloyd
    Very nice summary. I, too, have found that 95F is ideal, IF a rapid rise is wanted (as in yeast pancakes, for example). Otherwise, I keep things cool. The gluten develops better is we don't rush things. I really like about 60F, which allows for hours of slow rise. Results in fabulous flavor!
    Reply
  2. TomS
    Baked a very thick dough pizza for 20minat 450F. Crusty on outside but moist (but not sticky/gluteny)on inside. Safe to assume all the yeast was killed? I'm guessing Yes since you say 140F already kills them.
    Reply
    1. TomS
      I suppose if they were not killed off, then by next morning the leftover pieces would have grown a lot in size?
      Reply
  3. Bernadine Colling
    Bernadine Colling
    Do you have any coupons that you can mail me, for all the different flours that you have. Thank you very much!
    Reply
    1. Whitney Barnes
      Hi Bernadine! I have forwarded your request to our Customer Service team. They'll send you some coupons in the mail.

      I've also edited your comment to remove your address. Thanks for being a loyal customer!
      Reply
  4. Gabi
    Thank you for this detailed explanation! I'm about to try and bake bread for the first time ever and was stopped right from the start not knowing what a good water temp is for the yeast. Somehow I feel much more optimistic now :)
    Reply
  5. Cheryl A Gucciardo
    Cheryl A Gucciardo
    After reading your thorough explanation of temperatures required for the different types of yeast, I wonder if 140F is the correct temp to be used when baking bread using Paul Hollywood's method of adding the yeast directly to the flour. Should the 140 deg water temp be used?
    Or is the yeast he is using in the UK different from what we have here in the US?
    Reply
    1. Whitney Barnes
      Hi Cheryl - without seeing his recipe it's hard to give recommendations. 140F water certainly seems too hot to have in direct contact with dry yeast. Our Customer Service team is happy to chat more and give specific recipe advice. You can reached them at 1-800-349-2173 or [email protected]
      Reply
  6. Christina
    Hello, I am very new to making homemade bread from scratch. To proof my dry yeast, what amount of sugar and water is needed please?
    Reply
    1. Whitney Barnes
      Hi Christina, it all depends on the recipe you're using. If you're trying your hand at bread baking for the first time, I highly recommend this No-Knead Artisan Bread Recipe! If you don't have Artisan Bread Flour on hand, you can also use Unbleached White All Purpose Flour instead.
      Reply
  7. Sara Govemran
    I am very confused. If using instant dry yeast, must I use liquid at 120-130, or can it be cool or cold water ?
    Reply
    1. Whitney Barnes
      Whitney Barnes
      Hi Sara, Instant Yeast is the very similar to Active Dry Yeast except that it is milled into finer particles, thus making it dissolve faster. This is why it can be mixed directly into dry ingredients and doesn't require proofing. Warm water is still needed to dissolve the yeast particles so they can become active. The higher water temperature is suggested for Instant Yeast to offset the ambient temperature of the dry ingredients. By the time all the ingredients are mixed together, the temperature will have dropped to the appropriate temp to activate the yeast. I hope this information is helpful! :)
      Reply
  8. Gerold Heggem
    Really good article but some seemingly contradictory info at the end, maybe I'm just not understanding. Could you clarify the temperatures listed:
    Water at -4°F means your yeast will be unable to ferment.
    Water at 68° to 104°F means that your yeast’s ability to grow will be hindered, and its growth rate will be reduced.
    Water at 68° to 81°F are probably the most favorable range for the yeast to grow and multiply in.
    Water at 79°F are considered the optimum temperature for achieving yeast multiplication.
    Water at 81° to 100°F is the optimum temperature range for the fermentation process.
    Water at 95°F is the fermentation temperature that yields the best result.
    Reply
  9. Carla
    I have an bread cook book from 1973 an in all the recipe call for the water temperature to be 120 to 130. Recipes today say that this will kill the yeast. Is the dry yeast different now?
    Reply
    1. Whitney Barnes
      Hi Carla - It's possible that the yeast-making process has changed, but I'm not sure. I would suggest going with the temperatures suggested in our post. Happy baking!
      Reply
  10. Peter
    Hi,
    I cold proof my pizza dough in a fridge at 37 degrees Fahrenheit for 3-5 days. Does this mean I should still activate the yeast at its optimal temperature at the start of the recipe? Or should I be mixing the yeast with cold water at the start of the recipe, to slow down the fermentation process?

    Thanks!
    Reply
    1. Whitney Barnes
      Hi Peter - if you're using Active Dry Yeast, you will likely still want to proof it in warm water so the yeast granules completely dissolve.
      Reply
  11. Sierra
    Hi I have a missing work and this is helping me to complete.
    Reply
  12. Christine Smith
    Help! Making ciabata bread, and I forgot to warm the milk when pouring into my flour/yeast mixture. Will it work? What can I do to fix this? :(
    Reply
    1. Whitney Barnes
      Hi Christine - as long as your yeast is fresh it's likely fine! Instant Yeast can be mixed directly into dough while Active Dry Yeast needs to be dissolved or "activated."
      Reply
  13. Alec Sanchez
    Hi, I'm a student from Clackamas Community College doing a lab report on fermenting yeast, I was wondering who was the author or publisher of this post. I have to cite my sources but I can't seem to find a specific author for this article.
    Reply
    1. Whitney Barnes
      Hi Alec - this blog post was not written by a single person, rather by a team at Bob's Red Mill. If you have more questions, please email us at [email protected]
      Reply
  14. Jean
    Baked my first loaf of no knead bread before reading this, it never rose. Didn't want to throw everything out, so baked it anyway. Not really good, can't wait to try again with your water temp recommendations.
    Reply
  15. Special Monkey
    I tried to use Bob's ADY recently but the recipe called for proofing it in cold water - my dough didn't rise in the fridge during an attempted cold ferment - I'm going to try to activate the yeast (and retry the cold ferment again) by taking the dough out to warm up at room temp for a few hours or more -

    i see your article says ... "With dry yeast, if your water is too cold, the yeast will not activate. Or, if they do wake up, they might release a substance that hinders the formation of gluten."

    Can you elaborate on the the substance that might hinder gluten formation when using cold water, where the yeast wake up later?

    I'm wondering if my potential dough-at-room-temperature wake up solution risks what you mention?
    Reply

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