By the time he reached his late 30s, Pete Rickert Jr. was fed up with supervising construction sites. "I got tired of yelling at grown men all day to do their job right," says Mr. Rickert, who lives in Danville, Pa.

Then he read about the trend toward packaging craft beer in cans rather than bottles or jugs. Because most craft brewers can't easily afford their own canning lines, a new type of company was popping up: mobile canners. These firms haul their equipment to breweries, spend a few hours filling cans, then...