If you live in Sydney - or Melbourne, or New York, or any capital city, really - chances are you know someone who's not-so-secretly harbouring a SCOBY at home. Maybe even you are. It's been hailed as an all-round health elixir for over 2000 years now, but kombucha - the tangy fermented tea made with live bacteria - has suddenly shifted from hippy drink to supermarket shelves and café menus the (Western) world over.

At brunch, it's not uncommon to find the conversation shifts from CelineMagic potion or poison? The truth about kombuchaline to SCOBYs - that's Symbiotic Culture of Bacteria and Yeast, for the uninitiated. A SCOBY is the starter culture essential for brewing your own kombucha. Simply add black or green tea (organic, obvs) and loads of sugar to the slimy, jelly-like substance that is a SCOBY, and you're on your way. Note: If you really want to see something disgusting, google kombucha SCOBY. The results aren't pretty.

Kombucha SCOBY's

The kombucha club will tell you that the tea does everything from aiding digestion to detoxifying the body, boosting immunity, preventing cancer and curbing sugar cravings. Thanks to the fermentation process, it's said to be packed with health-promoting probiotics, which are essential for good gut health. It's an area dietitian Susie Burrell knows all about - her Shape Me program is designed for people with gut issues. But the nutrition expert hasn't jumped on the kombucha bandwagon.

Magic potion or poison? The truth about kombucha

"There is no doubt that as a result of stressful lives and more processed diets, more individuals are dealing with issues of gut dysfunction," she says. "There's an increase in demand for foods that contain probiotics, which help to support gut health." Enter kombucha (not to mention the rest of the special K's).

But Burrell stresses that kombucha isn't the ultimate cure-all it's claimed to be. "There is no one food that holds the answer to health," she explains. "It's about dietary patterns long-term and kombucha, like any foods that contain probiotics, can be part of that." Can't be bothered with kombucha? Yoghurt is just as good.

Homemade kombucha

What's worrying are the health concerns that home-brewed kombucha has raised. While a  2003 review concluded that there's no clinical evidence to support all of kombucha's health claims, a 2009 study revealed alarming cases of life-threatening lactic acidosis and hepatic dysfunction as a result of sipping the stuff. "While kombucha tea is considered a healthy elixir, the limited evidence currently available raises considerable concern that it may pose serious health risks," the study's authors concluded. Scary stuff.

Less extreme side effects to kombucha home-brew include nausea and allergic reactions, mainly to moulds that can develop during the fermentation process. Heavy metal poisoning has also been documented in cases where the kombucha was made in glazed ceramic vessels (stick to glass). Of course, cases like these are rare, and provided you're drinking store-bought kombucha, you have nothing to worry about.

To be on the safe side, only drink home-made kombucha if you're sure it's been done properly, with a mould-free SCOBY (the ones you can find in a Google image search probably don't fit the bill...) and in sterile conditions. Experts advise that infants and pregnant women avoid drinking it entirely. 

Magic potion or poison? The truth about kombucha