By Karen Gaudette Brewer

If you live in a kombucha-crazed city, chances are high someone you know is giving away a kombucha "mother" so that others can brew their own effervescent, fermented, probiotic-rich tea at home. Should you accept?

Yes—with a few caveats, says Cynthia Lair. She's a cookbook author, fermented foods fan, and assistant professor in the School of Nutrition and Exercise Science at Bastyr University outside Seattle.

"They do get passed along quite a bit and I don't think there's any problem with it," Lair says. She notes that it's quite easy to tell when something is off. Avoid these three telltale signs of fermentation gone wrong:

1. A putrid scent

A kombucha mother, also known as a SCOBY (Symbiotic Culture of Bacteria and Yeast) should smell tart or like vinegar. It should already be living in some existing kombucha, so a smart move is to taste that batch, says Lair. "Look at it, smell it, taste it. Good to go? Go!"

2. A creamy film, especially if it's the color pink

3. Mold
"As long as none of those things are going on, you should be fine," Lair says. After all, the whole objective of fermentation is to render the environment safe for good bacteria to grow and inhospitable to mold and other spoilage. "You have to have something go wrong for the bad guys to take over."

Now: Let's brew some kombucha!
Check out this excellent how-to guide from our friends at The Kitchn.