This article is from the Food Preserving FAQ, by Eric Decker firstname.lastname@example.org with numerous contributions by others.
These products may be safely canned only according to USDA guidelines. Piece
size, packing density and process times must be followed. Grated carrots can
not be safely processed according to times for carrot chunks. Pumpkin puree
can not be safely canned. The density varies too much, according to variety
and preparation method, to give safe recommendations. Only pumpkin chunks
may be canned. Addition of aspirin, salt, or "canning powders" will not
increase the safety or allow for reduced process times. Deviations from the
specified procedures might not be safe. The only safe recommendations that
can be given for other procedures is to freeze or refrigerate the product.
[There you have it. Don't bother asking for a pumpkin-butter recipe.
Fruits and vegetables may be pickled. In this case the guidelines for
pickled products should be used.