A nano is an infinitesimally small unit of measurement, one billionth. So, a nanobrewery is a teeny tiny brewery. \u201cWe\u2019re talking super-duper small,\u201d quips Julia Herz, Craft Beer Program Director for the Boulder, Colo.-based Brewers Association. Nanobrewers are a nano niche between homebrewers and microbreweries. They are ultra-enthusiastic homebrewers dabbling in limited commerce.\r\n\r\nAlthough experts admit nanobrewing is definitely a trend, no one can say for sure how many nanobrewers are out there. Counts vary from a score scattered about the United States to over a hundred nanobrewers in operation. And for now, there isn\u2019t even a definition of what constitutes nanobrewing.\r\n\r\n"In my informal definition, most of these guys are essentially selling to their backyards, friends and family network and maybe a [restaurant] account or two,\u201d says Herz. She estimates production at fewer than 100 barrels a year, many produce only a dozen. In contrast, big brewers produce over 2 million barrels annually, and even so-called microbreweries brew up to 15,000 barrels.\r\n\r\nWhatever the size of their production, the nano phenomenon is big enough to have caught the Fed\u2019s attention. The Alcohol and Tobacco Tax and Trade Bureau (TTB) warns enterprising homebrewers, that while households can legally make up to 200 gallons for personal and family consumption, once they start selling the stuff, they owe excise taxes\u2013no matter how small the amount.\r\n\r\nIndeed, nascent brewers need both federal and state licenses to sell their beer. Getting these permits can be a long, costly and arduous process. \u201cYou\u2019ve got to be dedicated if you are going to go nano,\u201d says Herz, citing numerous hurdles facing home hobbyists aspiring to go legit. It may take years before they see any profit.\u00a0 \u201cThey\u2019re doing it mostly for the love.\u201d\r\n\r\nSome nanobreweries are as fleeting as a quark particle, but new ones spring up all the time. Among the new nanos are Black Husky Brewing in Eagle River, Wis., Cave Mountain Brewing in Windham, N.Y., and Mattingly Brewing Co., which hails from Bud Country, St. Louis, Mo. Although the nano tag is a newly coined term, the impulse is not.\r\n\r\nMore than half of professional brewers today started out as homebrewers, according to the Brewers Association. And with an estimated 750,000 regular homebrewers out there, more will undoubtedly be bitten by the nano bug. Which means more beer choices\u2013right from your backyard.\r\n\r\nAlso read Who's Afraid of the Big Bad Brett?\u00a0for more information on beer brewing trends.