My kids are all geared up for tomorrow’s annual trick-or-treating. They’ve already found the stash of candy we’ve stockpiled for the neighborhood ghouls and are making trades for stuff they don’t even have yet (‘I’ll trade all my Skittles for all of your Twix’).

We’ll hit a couple of Hallowe’en parties this weekend and if there’s home-canned pumpkin butter served on the potluck tables, I’ll be avoiding it.

According to lots of folks in the home canning world, winter squashes like pumpkin are cool to can – in cubed form. The Plainsman has a good science-based discussion of why mashed winter squashes are problematic for safe canning: they are thick and end up with variable pH when acidified.

“Pumpkin butter recipes often have acid, such as vinegar or lemon juice, added to reduce the pH level below 4.6 which is a level at which the pathogen Clostridium botulinum will grow,” Joan Hegerfeld-Baker, Assistant Professor & SDSU Extension Food Safety Specialist said.

Food safety concerns related to pumpkin butter were studied by the University of Missouri in 1995. “Their research determined that pumpkin butters produced by home canners and small commercial processors in Missouri had extreme variations in pH values. Some pumpkin butters pH values were as high as 5.4, a level that supports the growth of pathogens of concern,” she said.

When the pH of home canned pumpkin butters, with added acid, was tested in South Dakota by SDSU Extension Food Safety Specialists, Hegerfeld-Baker said similar results were observed. “The pH levels of three samples of pumpkin butter sent in by a home food processor ranged from 4.5 to 4.8,” she said.

Pumpkin and squash butters have two inherent risks — pH greater than 4.6 and thick viscosity. “The pH is difficult to control, and the thick viscosity does not allow for good heat penetration when processing in a boiling water bath or pressure canner,” Hegerfeld-Baker said.

In 1989, the USDA Extension Service Published the Complete Guide to Home Canning. This has served as the standard for Home Food Preservation, with recommended and tested home processing techniques. However, in 1994 a revision was made: the only directions for canning pumpkin and winter squash is to cube the squash or pumpkin and process in a pressure canner.