Don't squish your squash when canning?! In other words, don't can mashed or pureed winter squash or pumpkin.
Research has found great variability in the viscosity or thickness of these products. In laboratory testing, the recommended time and pressure for processing was often not adequate to can winter squash or pumpkin safely. As a result, in 1994 USDA removed directions for canning mashed or pureed winter squash and pumpkin from the Complete Guide to Home Canning. So if you have a recipe for canning mashed or pureed winter squash or pumpkin, consider it out of date and don't use it. To read more detail go to http://www.uga.edu/nchfp/publications/uga/pumpkin_butter.html
It is okay to can winter squash and pumpkin in cubes. The product is not as dense in this form and can be safely processed. Directions are available at http://www.uga.edu/nchfp/how/can_04/pumpkin_winter_squash.html.
Another option is to freeze squash or pumpkin. Find directions for freezing winter squash at http://www.uga.edu/nchfp/how/freeze/squash_winter.html and for pumpkin see http://www.uga.edu/nchfp/how/freeze/pumpkin.html.
USDA also recommends that pumpkin butter not be canned at home. Research has shown similar safety problems as with plain pumpkin. It is best to freeze pumpkin butter if you make it.