Canning Pumpkin Butter and Mashed or Pureed Squashes
Elizabeth L. Andress, Ph.D.
Associate Professor and Extension Food Safety Specialist,
Department of Foods and Nutrition
Home canning is not recommended for pumpkin butter
or any mashed or pureed pumpkin or winter squash. In 1989, the USDA's Extension
Service published the Complete Guide to Home Canning that remains the
basis of Extension recommendations today, found in the September 1994
revision. The only directions for canning pumpkin and winter squash are for
cubed pulp. In fact, the directions for preparing the product include the
statement, "Caution: Do not mash or puree."
In accordance with the USDA recommendations, the University of
Georgia Cooperative Extension Service does not have a recommendation for canning
these products either. 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 and any publications
preceding the Complete Guide to Home Canning (September 1994) are
considered out of date.
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,
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
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.
Reprinted with permission from the University of Georgia.
Andress, E. (1997). Canning Pumpkin Butter and Mashed or Pureed Squashes. Athens, GA: University of Georgia, Cooperative Extension Service.
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