The process for homemade, hand-cranked ice cream "is a very complex
system," says Bruce Tharp, an industrial ice cream consultant and
adjunct professor who teaches a class on ice cream making at Penn State
University. The all-American treat finds some of its biggest fans on July Fourth, but a Ben & Jerry's product developer advises
would-be homemade makers that adding too much fat to a recipe, such as
chunks of peanut butter, would actually cause "buttering off" and
make the ice cream too hard.