It is not safe to home-can pureed pumpkin or any other winter squash (acorn squash, spaghetti squash, butternut squash, etc.). Only cubed squash is safe for home canning.
Canning pureed or mashed pumpkin is unsafe because it is too thick (or viscous) to enable the heat to fully penetrate the product during the canning process. Additionally, research has shown that both viscosity and pH (acidity) are highly variable between batches, making a standard processing time impossible, and unsafe, to determine. Winter squashes are considered low-acid foods (pH >4.6); therefore, if processed incorrectly while canning, these foods have the capacity to support the growth of Clostridium botulinum.
The best option for preserving pureed pumpkin or other squashes is to freeze the product in a freezer bag or plastic container.
Pumpkin butter is a nutrient-rich lower sugar alternative to jam. Make your own:
Ingredients: 1/4 cup water; 1/4 cup packed brown sugar; 2 tablespoons sugar; 3/4 teaspoon each: cinnamon, cloves, nutmeg; 15 ounce can 100% pumpkin puree.
Combine all ingredients except pumpkin in a 1 quart microwaveable bowl. Mix. Microwave on HIGH for 3 minutes. Mix in pumpkin puree and stir well. Microwave on HIGH for 5 minutes.
Keeps in the refrigerator for several weeks.