Apparently it's called a picobrewery. I doubt you can get much smaller than that, which is how Butcher Brew, a one-barrel Warren, VT, brewery now in development describes itself.
The man behind the effort is Steve Butcher, a former Michigan resident who moved to Vermont in 1999. He is a longtime home brewer who decided to go pro in a business he has set up in the basement of his barn, not far from the famous Sugarbush Resort in the central part of the state.
Butcher is aiming for a spring debut for his kegs and bottles, to be distributed locally via the Mad River Food Hub.
Here's how he describes his journey: "I started Butcher Beer in Vermont officially in 2015 by incorporating and starting the Federal Brewer’s Notice process. After 18 months of brewing three out of four weekends -- and some weekdays -- a month, revision upon revision of recipes and many, many tastings with friends, I decided it was time to get serious."
• Go here for Notes On Napkins
• Go here for Dowd On Drinks
• Go here for Dowd's New York Wines Notebook