Commercial canned pumpkin puree is an agricultural miracle of consistency, yet it poses serious mechanical hurdles for bakers. Most cans pack varieties of Dickinson squash bred for vivid orange flesh and shelf stability rather than low moisture. Introduce standard vegetable oil into that equation, and the emulsion drowns the flour’s starch granules.
When starch granules swim in unbound liquid, gluten proteins either overdevelop into a dense, gummy layer or collapse into soggy breadiness. Vegetable oil provides 100% pure fat with zero water, but it delivers flat, neutral notes. It lubricates the crumb without building any structural character. Traditional bar cookies require fat to do two jobs: tenderize the gluten network and carry lipid-soluble spice volatiles to your palate.
Swapping neutral oils for standard melted butter helps, but un-browned dairy butter still retains roughly 16% to 18% water. Add four large eggs and a cup of vegetable fat to a 15-ounce can of squash puree, and your oven must evaporate nearly two cups of surplus liquid before the crumb can set. The inevitable result is an overbaked crust housing an underbaked, soggy center.
