Here's a link to an interesting article that explains WHY pumpkin puree should not be canned, either by BWB or Pressure Canning. I thought it was clear and concise. According to the bio, the author is a master food preserver and canning expert of Growing A Greener World (PBS). This article is posted on her blog at livinghomegrown.com.

Jill

Here is a link that might be useful: Why Canned Pumpkin Puree is a No No