Why Can't I Make Home-Canned Pumpkin Puree, Pumpkin Butter,
or Pumpkin Pie
(including those made from winter
squashes, like butternut, hubbard, acorn, etc.)
I get asked this question a lot! You may can it in a cooked, cubed form; just not as a puree or ready-pumpkin pie filling. (see this page for instructions about how to can it in cubed form). Of course, you can freeze it, too, in cubed or puree or ready filling form (see this page for those instructions). And while I do have a recipe for canning pumpkin butter, I still keep the jars in the back of the fridge until I use them. Here's the reason!
According to The National Center for Home Food Preservation (a land-grant university consortium sponsored by the USDA, and considered to be the leading authorities on food safety science and food preservation research) (and I am quoting them here):
“Home canning is not recommended for pumpkin butter or any mashed or pureed pumpkin or winter squash, but we do have directions for canning cubed pumpkin. Pumpkin puree can be frozen or made into a spicy pumpkin leather…
There are not sufficient data available to allow establishing safe processing times for any of these types of products. It is true that previous USDA recommendations had directions for canning mashed winter squash, but USDA withdrew those recommendations…
Some of the factors that are critical to the safety of canned pumpkin products are the viscosity (thickness), the acidity and the water activity. Studies conducted at the University of Minnesota in the 1970's indicated that there was too much variation in viscosity among different batches of prepared pumpkin purees to permit calculation of a single processing recommendation that would cover the potential variation among products (Zottola et. al, 1978). Pumpkin and winter squash are also low-acid foods (pH > 4.6) capable of supporting the growth of Clostridium botulinum bacteria which can cause the very serious illness, botulism, under the right storage conditions. If the bacteria are present and survive processing, and the product has a high enough water activity, they can thrive and produce toxin in the product.
More recent research with pumpkin butter has been done at the University of Missouri. Pumpkin butter is mashed or pureed pumpkin that has had large quantities of sugar added to it, but not always enough to inhibit pathogens. Sometimes an ingredient such as vinegar or lemon juice is added to the formulation to increase the acidity (decrease the pH). However, pumpkin butters produced by home canners and small commercial processors in Missouri have had pH values as high as 5.4. In fact, the pH values seemed to be extremely variable between batches made by the same formulation (Holt, 1995).
It is not possible at this point to evaluate a recipe for pumpkin or mashed squash for canning potential by looking at it. At this point, research seems to indicate variability of the products is great, and in several ways that raise safety concerns. It is best to freeze pumpkin butters or mashed squash.” (emphasis added)
Obviously, pumpkin pie filling is essentially “pureed pumpkin” and similar to pumpkin butter. This means that neither the cooked pumpkin puree nor the pumpkin pie filling (puree plus sugar and spices) would be candidates for safe home canning.
The University of Illinois Extension also says: “Canning pumpkin butter not a good idea, but try pieces or freezing. “
- Canning Pumpkin Butter and Mashed or Pureed Squashes: http://www.uga.edu/nchfp/publications/uga/pumpkin_butter.html
- Extension Service, USDA. 1994. Complete Guide to Home Canning. AIB No. 539. U.S. Department of Agriculture, Washington, DC.
- Holt, D. September 22, 1995. Re: Pumpkin butter. Email message to email@example.com.
- Zottola, E. A., Wolf, I.D., Norsiden, K.L. and D.R. Thompson. 1978. Home canning of food: Evaluation of current recommended methods. Jn. of Food Science 43:1731.
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