I have always felt that a reasonable definition for nanobrewery was any brewery using a three-barrel system or smaller, and now I see I'm correct. John Holl has a nice piece on nanos at craftbeer.com, and that's the definition he uses. His source? Me.
Nano-breweries, sometimes referred to as pico breweries, or bucket breweries, distribute to a limited area and only make beer in very small quantities.Now, if only someone would call to ask my opinion on whether beers fermented with brettanomyces can properly be called sour, we'd be all set.
How Small are Nano-Breweries?
"My working definition is three barrels or less, which essentially makes them large-scale homebrewers," said Jeff Alworth, author of the Portland-based beer blog Beervana.