EVERYTHING David Zhou does comes back to the Chinese Tao philosophical understanding of yin-yang, the balance, literally, of dark and light.

Which is just as well. Right at the minute, the Shanghai-born restaurateur is balancing quite a bit on his plate: he has just relaunched his flagship restaurant, David's, in Prahran; opened his fourth Oriental Teahouse restaurant and shop last year (and is ready to consider more); and has an Asian-themed bar in the pipeline to open early next year.

But it's the yin and the yang of the tea leaf and its medicinal qualities, for the moment, that is the focus of our discussion - more particularly, how different brews are designed to regulate the body's wellbeing (in Tao talk, the balance of hot and cold).

''Tea helps everything,'' says Zhou, explaining that our ginger barley cuppa he has chosen is excellent for circulation, given the weather's biting outside.

He leads me on a merry chat through his signature blends and when to drink them - Iron Buddha, a mix of green and red leaf, during meals to help metabolism; Relaxing, with its liquorice, wolfberry and ginseng notes, for nourishing the brain … well, any time. But also when not to. For instance, avoid black tea when the body is stressed or ''too hot''. He once took time to prescribe diners a particular blend depending on their appearance, until business just grew too busy.

Zhou may describe, somewhat humbly, tea as his hobby, but his interest goes much deeper. Without it, the business he has built wouldn't exist.

As a 29-year-old, Zhou came to Melbourne in 1989 to escape the ''boredom'' of Shanghai, where he taught a combination of martial arts and traditional Chinese medicine, both intimately rooted in yin-yang.

Initially, he struggled to find his feet in a foreign city with almost no language and no contacts; at one point he slept overnight in a bathtub. Joined a year later by his wife, Kathy - whom he admits has the business smarts in the partnership - he eventually opened a small shop in Windsor, from where he sold his blends of imported herbal teas wrapped in plain butcher's paper.

In the mid-'90s, the council demanded Zhou apply for a restaurant licence when he tried to set up a single table and chair in his tea warehouse in Cecil Place, still the site of David's, so people could sample his tea with food. ''That's how I started,'' he says.

This was the opportunity to showcase Shanghai cooking. In the 13 years since, David's has scored chef's hats from The Age Good Food Guide in 11 of them. Even though, as Zhou tells the story, he sent a reviewer packing early on when he mistook discreetness for rudeness; and another about an Age editor who became testy when not given a better table.

David's has now swapped its dark, formal decor for more casual, softer-looking white-painted timber (with spots of black for balance) and had its menu rejigged to feature small, country-style dishes, reflecting our increasingly relaxed eating-out habits.

''It's not just a reno, but a revolution, a new direction,'' Zhou says. ''It's like eating with the family.''

His Oriental Teahouses - which serve dumplings made fresh on the premises, ideally

paired with tea - have anticipated this trend to some extent, with Zhou ever the businessman open to franchising the enterprise, if - and it's a big ''if'', because he's fielded many inquiries - the partner shares a similar sensibility and outlook.

That outlook now includes plans for an Asian cocktail and dumpling bar in St Kilda's Fitzroy Street on the site of the old Catani Bar.

Zhou believes he's onto something new with the bar. ''We have set so many trends - sharing small dishes, Shanghai cuisine, tea cocktails,'' he says. ''We'll set another trend.''

But he's remaining tight-lipped on details. In the same way non-Asian restaurateurs have opened Asiatic ventures, Zhou expects others will follow his lead.

''I'm waiting for Neil Perry, all these [kinds of] people, to start to copy this,'' he said.