Kombucha -- the cold, fizzy tea that claims to have all kinds of health benefits -- has come under government scrutiny. Because it’s fermented, kombucha usually has some trace amount of alcohol in it. In the past month, the U.S. Alcohol and Tobacco Tax and Trade Bureau has been cracking down on kombucha makers. The agency sent warning letters to kombucha makers whose products contain even the slightest bit more than .5 percent alcohol. That’s the threshold for officially qualifying as booze. And if you’re making booze, you have to abide by a whole bunch of special regulations. Behind this scrutiny is the exploding popularity of the drink. Once an obscure hippie concoction, kombucha is now a $.6 billion a year industry. It’s expected to reach nearly $2 billion in the next five years.