When looking for canning recipes for potatoes and pumpkins/squash, all recipes call for cubing and pressure canning. I want to puree my pumpkin and squash before canning. Can I do that?
What is the difference between canning a thick tomato sauce or pumpkin puree which is about the same consistency as my tomato sauce?
Density of canned foods
The reason you are only finding cubed recipes is because that is the only safe way to pressure can winter squash and potatoes. Once pureed, the density becomes problematic and it can be too thick for the heat to adequately penetrate the jars. The circulation of water between the cubes allows for the heat to fully penetrate and be safely pressure canned. If you want a pureed soup or squash, we recommend canning in cubes as and then using an immersion blender or regular blender to puree when you open the jar to use later on.
Here are some helpful resources:
- Cubed Squash and Pumpkin recipe, National Center for Home Food Preservation
- PNW 172 Canning Vegetables, WSU Extension
Acidity of canned foods
To answer the second part of your question, there are a couple of key differences between tomato sauce and pumpkin puree:
- Tomatoes are a higher acid (lower pH) product
- Tomatoes are acidified with citric acid, lemon juice, or vinegar before canning to further acidify them and render them safe
- Tomatoes have been tested in various forms for safety and appropriate times and recipes developed for those forms.
Pumpkin is a much lower acid (higher pH) product and we do not acidify them. Unfortunately, pureed pumpkin has not been tested the same as tomatoes for home canning, so it is still not safe to can the pumpkins in pureed form.