What is kombucha and why are Chinese youth obsessed with the fermentation health trend?

Young people in China are homemaking kombucha, reviving a 1980s fad from the previous generation after the drink became a globally recognised health product.
In recent years, kombucha has gone viral in Western countries as a commercial beverage, endorsed by stars such as Kourtney Kardashian and Lady Gaga.
The trend has reached China and prompted some drinks makers to release kombucha products. Meanwhile, some Chinese youngsters are making their own kombucha at home and sharing their methods...