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Why Canned Pumpkin Puree is a No No

Do Not Can Pumpkin Puree -

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 -

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 -

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 -

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®. For 9 years, Theresa was 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 sons and several disorderly but totally adorable chickens. Learn more about Living Homegrown here and about the Canning Academy here.