Who doesn’t love warm pumpkin pie in the Fall and a hot bowl of squash stew in Winter? People ask me all the time, “Is it possible to can pumpkin and squash?” Of course, it is possible, but for the home-canner (and especially beginners) the simple answer is: No! The answer as to why lies in the parameters for food safety specifically laid out by the USDA. Simply put, pumpkin and squash are very low acid foods and because the consistency of pureed pumpkin and squash so often varies, officials have been unable to set forth safe canning procedures for this type of produce. Although, they explain, you may can it in a cooked, cubed form: see this page for instructions about how to can it in cubed form. You can always freeze it, too, in cubed or pureed or ready pie-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. Below is the article that explains food safety regulations for canning/not canning pumpkin and other squash. Canning and Preserving are easy and fun but it is key to follow safety procedures at all time.
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. “
See you in class