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Why Canned Pumpkin Puree is a No No

Do Not Can Pumpkin Puree - LivingHomegrown.com

I get asked about canning pumpkin every October.

Fall is in the air. We are gearing up to carve pumpkins for Halloween and the idea of warm pumpkin pie is on our mind.

Many are in the mood to make a canned pumpkin product and might be considering something like pumpkin puree or even pumpkin butter.

So it is only natural that the questions about how to water bath or pressure can pumpkin puree and pumpkin butter are starting to come in. So here is my answer:

Don’t do it.

Don’t water bath it.

Don’t pressure can it.

Here’s why it is dangerous and what you can do instead…

Do Not Can Pumpkin Puree - LivingHomegrown.com

Why Canning Pumpkin Puree is Unsafe:

It is not recommended that you water bath can or pressure can pureed pumpkin for three specific reasons:

pH Level:  Pumpkin is a low acid food and should never be considered for water bath canning because low acid foods can harbor and grow the Clostridium botulinum bacteria which can cause botulism. And no, you can’t just add some lemon juice and call it a day. The acid level can vary so much from one pumpkin to the next, it is impossible to guarantee a safe recipe standard. (This is discussed in more detail below)

Viscosity (thickness): Most pumpkin puree is very thick and that thickness can vary for each pumpkin and within the jar itself. This thickness makes it difficult for temperatures to penetrate (even under the pressure of a pressure canner). The discrepancy in the viscosity makes it is impossible to layout a uniform recommendation for pressure canning pressures and timing. If the proper temperature is not met in the center of the puree and held there for the required amount of time, the botulism spore can survive the process. If a spore is held in an anaerobic environment at room temperature (like a canning jar), it will grow and multiply.

Water Activity: This is a mathematical formula used in food safety and preservation to calculate how well a substance can support microbial activity (which directly relates to how long something can be safely stored on a shelf). When it comes to pumpkin (or any summer squash) the water activity varies greatly within any given species. This makes timing recommendations impossible to guarantee safety.

The Bottom Line:

So in other words, there are many variations not only among the different types of pumpkins but also within each pumpkin family. These variations make it difficult to create safe canning recommendations that will work universally for all pumpkin recipes.

So the recommendation is to never water bath or pressure can any form of pumpkin puree or pumpkin butter.

Do Not Can Pumpkin Puree - LivingHomegrown.com

Think Like a Gardener:

You might wonder why things would be so different from one squash to the next.

But, when you look at this from a gardener’s standpoint, the idea of a large squash variation makes perfect sense. A squash is an open pollenated plant. This means that the plants can freely intermix with other squash varieties planted nearby.

When you save seed from squash that mixed with other squashes (even within the same species), there will be variances. Seed can vary from region to region and from year to year. This is especially true with home gardeners who may be saving seed after growing several different squash plants within a small space.

But Don’t Some Internet Sites Say it is Okay?

Yes, there are sites on the Internet that say if you just add a little lemon juice it is perfect safe to can. Some even say it is safe to water bath can.

This is untrue.

Although lemon juice will change the pH, it is a guessing game. So the truth is that it “might” be safe.

  • Listen, pH all depends upon the acidity of that particular pumpkin. There are huge variances on squash acidity within the same pumpkin variety and even within the same batch of pumpkins from the same field. That is precisely why it is not recommended.
  • If you try adding lemon juice or other acid to a recipe, you might get lucky and make your batch acidic enough. Or you might not. And when we are talking about botulism and sickness, only you can decide if it is worth the risk.

Everyone has to decide what they are comfortable with doing.

Do Not Can Pumpkin Puree - LivingHomegrown.com

Why Do Old Canning Books Have Recipes?

Yes, you will find canned pumpkin puree recipes in very old canning books. About 25-30 years ago, even the USDA had standard recipes with pumpkin that could be pressure canned.

However, university testing occurred in the 1970’s, 80’s and 90’s and all studies came back with the large variances I listed above. Because of that, the canning standards were changed across the board in the 1980’s and remained in affect during the major canning standard changes of 1994.

This is why it is always recommended that you use books that follow the most recent canning recommendations of 1994 to present day.

What to Do Instead:

You can pressure can pumpkin or summer squash in a jar if you process it as cubes. This is so that heat can freely circulate around it and penetrate the cubes inside. Here is information on how to do that: Pressure Canning Cubed Pumpkin.

But I recommend freezing pumpkin puree. It is fast, easy and gives really great results.

What About You?

There are SO many things we can do with fresh or frozen pumpkin puree. I make the usual things like pumpkin pie and pumpkin bread. But I would love to know what you do with pumpkin in your kitchen.

If you have any recipes, tips and ideas, please post them in the comments!

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About the Author:

Theresa Loe is the founder of Living Homegrown® and the Canning Academy® and is the Co-Executive Producer & Canning Expert on the national PBS gardening series, Growing A Greener World®. Theresa homesteads on just 1/10th of an acre in Los Angeles with her husband, two teenage boys and several disorderly but totally adorable chickens. Learn more about Living Homegrown here and about the Canning Academy here.

41 Comments:

  • Karen says:

    We moved to our little farm four months ago. A dear friend brought us a variety of winter squash starts. I was very excited because I have always wanted to grow it but I have never had the space. Now we have plenty of space. The squash are HUGE. They are growing into the grass, they have made it impossible to fine my cucumbers and they are even growing on the boysenberry vines. We are going to try to store them and use them as our winter veggie. I also plan on pureeing what I can’t store/use and freezing it. I will probably also try PC it in cubes for use in soup.

  • Seahare says:

    What of the fruit butters like plum and apple? Mine are thick enough a spoon stands up.

    • theresa says:

      Hi Seahare,

      In the case of plum and apple fruit butters (and most fruit preserves), you are safe because they are high acid foods. Their pH is such that you do not have to worry about botulism at all. So even though they are thick, botulism is not an issue.

  • Brian says:

    The “old timey” variety we get in NC keep very well whole. This is the pale skinned with bright orange flesh pumpkin. We process and freeze quite a bit but always end up with one or two that just sit there for a couple of months. You have to keep an eye on them, and put them in a sheet pan in case they decide to go bad.

  • Why is it then OK to PRESSURE meat? Meat has to be denser than Pumpkin Puree? How do the major processors do it and make it safe?

    • theresa says:

      Excellent question Michael-

      I believe it has to do with the following:

      1) Meat actually has more consistent air, water and most importantly fat molecules with in it. This allows for better heat penetration.

      2) But more importantly, the water activity of meat (which is a mathematical formula for determining humidity balance) is very consistent (unlike squash). So a standardized amount of time/pressure can be determined for all meat recipes. In other words, because scientists can show that meat always falls within a certain range of water activity, we know exactly what time/pressure is needed to make that meat safe. Squash has too many variances to make that same determination.

      Here is a paper that explains water activity determination in meat: http://www.equinlab.com/pdf_/Influencia%20de%20la%20actividad%20de%20agua%20(aw)%20en%20productos%20carnicos.pdf

      How do commercial companies can pumpkin?
      First, they use the same squash variety (or same blend) every time and they have quality control to test the pH and water activity to be sure they know the range. They can use a standard time/pressure/heat combo because they always verify their batch is kept within that range.

      Our problem as home canners is that we may use any of many squash choices. A recipe that was developed for a certain range may not work with what we chose or with the particular squash we grew ourselves. Yes, we could do what the commercial producers do and test the pH and the water activity (using the formula here http://en.wikipedia.org/wiki/Water_activity ) and then figure out what the time/pressure requirements are for that particular range but that is beyond what most home canners would be able to do themselves.

      I hope that helps.

  • Beth in Ky says:

    I don’t see this as even an issue…. you just can in cubes in a pressure canner at recommended time. Then set jars on the counter a couple of days. Check the seals, then SHAKE! Waaalllaaa! Pumpkin puree. Or don’t even do that just drain, dump in your recipe and mix, especially if you are using a mixer it is puree within 2.3 seconds. (This is not an idea,, I really do it this way)

  • WendP says:

    We do the usual things with pumpkin – quick sweet bread, cheesecake, pie, pudding. We even do pumpkin granolas & smoothies. I’ve been trying to find more savory pumpkin recipes our household will eat. We like chicken broth-based pumpkin soup and I’ve started mixing pumpkin into lentil soup as the starch instead of potatoes.

  • Brandon Coppin says:

    Great info! I’ve been wanting to try canning pumpkin. I’ll just freeze it instead 🙂

  • theresa says:

    Gosh Lynn,
    I’m sorry to hear about your friend. I don’t really think I can answer that one. There are 100s of plants that can cross in the squash family and I really am unsure what you had there. I have never heard of a toxic squash of any kind. Plus you did not say how the squash was prepared. Was it canned? Was it cooked fresh? I am sorry I can’t help you on this one.

    • Lynn says:

      So sorry…I just got my information straight! The squash that made my friend ill was crossed with a gourd. That would explain it!! So I ran out to my garden in the dark tonight and harvested my few cross-breeds before they endure yet another frosty night. I’m hoping for some extra-tasty spaghetti squash (I love Delicata!), but it looks like there might be more of a zucchini influence going on here… we’ll see! Thanks so much for your time and response!

  • theresa says:

    Hi Millie,

    You can NOT safely can pumpkin in a water bath even if it is cooked. Cooking will only kill the active bacteria but not the spores. Once canned the spores can start to reproduce if the pH is not perfect and create the toxin that will make you sick. Do not can pumpkin in a water bath.

  • Nita Rauch says:

    why does my comment need moderation?

    • theresa says:

      Hi Nita,

      I’m sorry that I have to keep the comments moderated. Like all bloggers, I get 100s of spam comments each day. My spam filter catches most of them. But not all. If I didn’t moderate them, we would have lots of spam mixed in and it would ruin the reader experience. 🙁

  • theresa says:

    Hi Nita,

    Sorry for the delay in answering you. I have been traveling as we wrapped up filming of the TV show.

    I would not do either of those options. I know that is not the answer you wanted. Sorry.

    You are working in the dark when you try to can pumpkin butter. Unless you pay to have the food to be professionally tested for pH and water activity, you really don’t know what you have – even if you use store bought. As you cook it down further, you are changing the water activity of that product.

    I would suggest picking a different gift idea or having your friends store the pumpkin butter in the refrigerator or freezer.

    • Nita Rauch says:

      Theresa: Yes, you are right; I’m not happy with the answer, but I understand. So, I was perusing another website that sells homemade jams/butters. They custom cook to order and state if not used in 2 months, to freeze the jar of pumpkin butter.
      Is 2 months at room temperature safe? Or should it have read “Freeze immediately upon receipt unless you will use within 2 months; then refrigeration is adequate.”
      Pumpkin butter is a BIG favorite and I’m still having a hard time wrapping my head around all those jars are made in the past as gifts and only recommended refrigeration after opening the jars. Sure glad I didn’t kill anyone with my gifts.

      Thanks for all your research on this topic. nj

      • theresa says:

        Gosh Nita – I’m not sure.

        Are you saying the jars are sealed in a canning jar but they are telling people to freeze them instead of storing them in the pantry? Or are they sending them overnight and asking you to refrigerate and then freeze if not used after 2 months? Also, is it pure pumpkin butter or a mix with another fruit (like apple). I don’t want to say their wording is wrong without really knowing what and how they are sending. So I guess I can’t answer you. Personally, I would not eat/buy a homemade pumpkin butter that is room temp in a jar unless it is made commercially. (Only because a company would be forced by regulations to test it.)

        And I’m sorry about the bad news with the pumpkin butter. It’s just a tricky food product. I don’t want to recommend anything to my readers that I would not do myself.

  • Heidi says:

    I did not have this information before I canned pumpkin last month. Even though I did the water bath, within two days I recognized that my seals had not held and the jars were leaking. I immediately put them in the freezer. Do you think they’re safe to use?

    • theresa says:

      Heidi – Normally, you have 24 hours to check a canning seal before moving a product to the refrigerator. However, since we know these were not quite safe to begin with I would worry that “within two days” may be cutting close.

      Here is a good rule of thumb: If the food you just put up could sit on a counter for that amount of time (in case: within two days) without ever being canning, would you feel safe eating it? In the case of something pickled, it would be okay. But would you leave pumpkin on your counter for two days unrefrigerated? In most cases, no. And that is essentially what may have happened here.

      When we are just talking about something going bad (like fruit), I would say it is okay. But in this case, we are talking about something more dangerous – potentially deadly. So, if it were me…no, I would not eat it. But you have to make the choice that you feel safest with.

      I wish I could you give you a happier answer. 🙁

  • Lynda Wilson says:

    Pumpkin bread freezes well. I make double batches with fresh pumpkin puree. I get the fresh taste and convenience of having it on hand. We’ve processed pumpkin puree to freeze from our Halloween pumpkins for years. This year we wanted to see if it could be canned. Your information saved us a lot of work! We might try canning chunks, though. Thanks!

  • Karen Rink says:

    I would love a pumpkin bread recipe. Can anyone send or post one?
    Thank you!

  • Donaldo says:

    Thank you for getting the correct information out to people!
    The way I store for later use my butternut and pumpkin is to dehydrate it.
    I cook the squash, then add it to my blender, add a little vegetable stock if needed to thin it (or you can use the cooking liquid) then pour it onto prepared fruit leather trays and dehydrate until very crispy. (it helps to turn the puree over to make sure the bottom side gets dry) then it is crumbled up and is ready for rehydrating when I want to use it in a recipe. You can even add pumpkin pie spice before you dehydrate it for a wonderful snack.

  • Emily says:

    Thank you for going in depth about the science behind why certain things are recommended or not recommended by NCHFP. I’m really surprised by blog posts and comment threads I’ve read about canning pumpkin. Many people assume because they haven’t gotten sick (or worse!) yet, their methods are fine – they know about the warnings but are comfortable continuing with potentially unsafe practices.

    Everyone has to make their own personal decisions regarding what they eat and how it is preserved, but think twice before sharing your goods with others or bringing them to a pot luck. As a home canner, your friends and family count on you doing it right as the expert! Read the article below if you’d like for why it’s so important.

    http://www.cnn.com/2015/04/28/health/potatoes-to-blame-for-botulism/

  • Marguerite Raes says:

    I just canned some pumpkin. If the seal remains good, is it safe to eat?

    • theresa says:

      Hi Marquerite-
      You didn’t give any details here, so I am not sure if you read the post above and are referring to pumpkin puree or cubed pumpkin or water bathed or pressure canned or if you followed a USDA recipe or something else. I sorry, but I can’t answer as to if what you did was safe or not. Sorry about that.

  • Mike says:

    Theresa: We followed with interest the string of messages posted because we have canned pumpkin for years, but never without baking it until completely soft first. Then the flesh is pureed and pressured canned according to the instructions that came with our canner. The canned pumpkin is used mostly for baking, but sometimes also to make pumpkin ice cream. We never got sick…have we just been lucky?

    • theresa says:

      Well Mike to be honest…yes. The bottom line is that you are working with a lot of unknowns here in the pH and water density. It sounds like your situation has always swung in your favor and that is great. But I would still not do it myself. I just don’t feel comfortable with unknowns when it comes to canning since they can fluctuate from year to year. It is a personal choice. But I totally understand that others are more risk takers than me. For me…freezing the pumpkin keeps it within my comfort zone.

      • Shar says:

        My question is, if the pH various so much, why couldn’t they set a standard that would cover the lowest pH they studied and leave it at that. Go with the worst case scenario so anything more acidic would fall under that anyway.

  • J says:

    Please help! Is Libby’s safe, as it is canned pumpkin? Thank you!

    • theresa says:

      This article is on HOME canning. Commercial canning is a VERY different thing.

      First, commercial food companies create a blending of pumpkins and that blending is tested constantly for quality control. They always know the pH, viscosity and water activity of that pumpkin and can adjust accordingly. That is standard in the food industry. Second, commercial processes use different temperatures, pressures etc that we cannot use in the home setting. Third, the entire process is monitored and quality control sampling is happening all the time. Commercial pumpkin is safe.

  • Trina says:

    Thank you so much for the informational post! I was just about to get started on canning some pumpkin but will be freezing instead!

  • Rachel says:

    Hi. Very interesting article. I have always frozen my pumpkin but want to can a few jars. So my question is: can the botulism spores develop if I store my jars of cubed pumpkin in the refrigerator? Thanks.

  • Susan says:

    Thanks! I came to google canning pumpkin, and got your answers. Saved me a lot of time, trouble, and possibly illness! I thought it would be quicker for last minute baking to have it canned rather than having to wait for it to thaw. I will just freeze my pumpkin puree. Better safe than sorry!

  • candy says:

    Thank you for this valuable information. I just tried my hand at canning this year (salsa and jam) wanted to can the halloween pumpkin but I will now freeze it. How long can it be frozen before it needs to be tossed?

    • theresa says:

      Typically, frozen pumpkin is kept for a year. After that, it loses a lot of its quality and nutrition. I shoot for 6 months for best results.

  • Cindy says:

    I have already made pumpkin soup and would like to can some of it. Is that safe to can or would you still recommend freezing?

  • Hannah says:

    I have previously frozen pumpkin and squash for very short periods of time (a few weeks or less than 6 months) and we always found that squashes do not taste good after being frozen. No one wants to eat anything I make when using frozen pumpkin even though the same recipie worked great with fresh pumpkin. Have you ever experienced this?

    • theresa says:

      I haven’t Hannah, but I freeze my pumpkin in puree form and then use it in cooked products. Are you talking about puree? If you are, then the most important thing is to make sure there is very little air in contact with the food. So if you place it inside of a container, you need to fill it and only leave about 1 inch space at the top (for expansion). If you are freezing your pumpkin in chunks to be eaten straight, then the squash must still be cooked before freezing to destroy an enzyme that deteriorates it during freezing.

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