Wolfgang Puck has been a celebrity chef for more than two decades and is a mainstay on cooking and television shows like Masterchef and The Ellen DeGeneres Show.

His restaurant Spago in West Hollywood, which he opened in 1982, is considered a pioneer of California-style cooking, and is still a celebrity hotspot more than 30 years on.

Amid all that success, Puck's business empire now brings in about $600 million each year, he told CNBC. That includes his fine dining restaurants, casual restaurants and merchandise like cookware, knives, coffee makers and rice steamers.

The restaurant industry is tough, though, and even celebrity chefs often struggle to convert fame into profit. Passion, the Austria-born chef said, is what's essential for those wanting to venture into the restaurant industry.

"They have to have passion for food, the passion for hospitality. It's not a business where you sit in an office and just look at the computer and numbers. The numbers come after. First, you have to make the customer happy," he told CNBC during a visit to his restaurants in Singapore.

The city-state played host to the first international outpost of Puck's fine dining empire, and the chef said that his Singapore restaurants are the most profitable — as labor costs are lower. Last year marked the restaurants' best year, he said.

Despite his own international outings, he cautioned that expansion is a risky business. The restaurant businesses need to "expand at a certain pace — not too much and not too little," he said.

"You have to make more money than you spend, that's my first thing — I didn't have to go to Harvard or Princeton for that."