Media playback is unsupported on your device Media caption The Californian trying to make wine like the French

Tech entrepreneur TJ Rodgers made billions of dollars founding silicon chip maker Cypress Semiconductors, now he has turned his sights to wine-making, and is on a quest to make the best Pinot Noir in the New World.

A collapse in the roof of a gigantic tunnel being driven into a hillside sounds like a pretty dramatic event.

But the entrepreneur TJ Rodgers is calm as he recalls what happened.

"It's not like you see in the movies with rocks flying, and stuff like that.

"It will kill you but it's kind of a slow motion thing, and you can walk [away] and stay in front of it," he explains.

He is speaking inside one of three giant caves that house his winery high in the Santa Cruz mountains in California.

Image caption Constructing the wine-making facility took years

The construction of the facility was a monumental task, taking years and requiring advice from experts in digging tunnels under the Austrian Alps.

Occasional cave-ins were just one of many challenges.

The location was so remote that it was impossible for concrete to be driven in without it setting first. Instead, they had to drive in a concrete-making plant which they assembled on site.

And the reason for all this intense effort? "Our mission statement is to make the best Pinot Noir [wine] in the New World," says Mr Rodgers.

Image caption TJ Rodgers became interested in wine in his youth

He is certainly not someone to do anything by halves. He founded the huge silicon chip maker Cypress Semiconductors in 1982, and subsequently built it into an enterprise worth billions of dollars.

The silicon chips that Cypress makes are found in millions of mobile phones and many other devices. Chips are also found on the bottles produced at the winery, which is called Clos de la Tech.

TJ Rodgers, who recently stood down from Cypress, first became interested in wine in his youth. Pinot Noir proved to be his favourite, in particular that made in Burgundy.

He wanted to know more, so he travelled to France, visiting vineyard after vineyard in Burgundy.

Despite the bemused responses from some vineyard owners, Mr Rodgers says he learnt a lot from his time in France.

Image caption TJ Rodgers has tried to replicate Burgundy's wine-making process in California's Santa Cruz mountains

Back in California, his interest blossomed into a passion. He set about trying to make wine himself, and he enlisted the help of his wife, Valeta Massey, who now spends much of her time on wine-making.

Mr Rodgers first experimented with a vineyard at his home. Later, after the purchase of the site in the Santa Cruz mountains, the venture became more ambitious.

The plan was to aim for the highest possible quality. The best way to do that, Mr Rodgers decided, was to copy the wine-making process used in Burgundy in the 1830s.

This meant using techniques such as foot-crushing the grapes, and being as gentle as possible with the wine at every stage.

Pumps are avoided. Instead, the facility is a "gravity winery", explains Mr Rodgers. The three enormous caves are arranged one above the other, so after fermentation in the topmost cave the wine flows through pipes downhill into barrels in the second cave for the next stages of the process.

Image caption Some technology is still involved in the wine-making process

Despite the emphasis on traditional methods, technology also plays a role. For example, many real-time measurements are taken during fermentation, and special devices are used to measure moisture levels in the field, helping to ensure the crops get exactly the right amount of water.

But Mr Rodgers is quick to add that modern techniques are only used where appropriate: "the technology is not to supplant the old process, the old guys were pretty smart."

TJ Rodgers is far from the only wealthy individual to try his hand at pushing the boundaries of wine-making in California. But are ventures like his little more than the wine-making equivalent of vanity publishing?

Not necessarily, says Aaron Pott, a wine-maker and consultant who has worked at the top end of the industry in France and California. With the right vineyard, and skilled staff, he says, it is perfectly possible to make excellent wine.

Mr Pott adds it would also be a mistake to assume that only ancient vines can produce good output. "Great wine can be made from young vineyards," he says.

Image caption The French oak barrels used at Clos de la Tech cost $1,000 (£774; 876 euros) each

But while it may be feasible to make high quality wine, making money in the process is more difficult, according to both Mr Rodgers and Mr Pott.

For one thing, there is the high cost of setting up facilities like those built by Mr Rodgers and other wealthy people in California. Quite apart from the cost of the land and buildings, the equipment can be expensive.

Take, for instance, the French oak barrels used at Clos de la Tech - these cost $1,000 (£774; 876 euros) each.

Then there is the question of yield. The downside of aiming for high quality, says Mr Rodgers, is that output will be small.

"Our yield up here is one tonne per acre. If you go to a commercial farm in Napa you see five tonnes per acre, and if you go to Modesto you see 12 tonnes per acre. Ok so right there, the war's over with regard to economics. Your wine's going to be expensive," he explains.

Image caption The grape is the most important part of the wine-making process

Nevertheless, although economics may present a challenge, benefits can flow from what Mr Rodgers and others like him are doing, says Mr Pott.

Whilst in some ways it may make it harder for smaller concerns like his own to compete, Mr Pott believes that the emergence of wealthy wine-makers in California has helped "to raise the bar" of quality - and that ultimately is a good thing for the industry.

TJ Rodgers and Valeta Massey say they have enjoyed their venture immensely, and that they have learnt a lot about wine in the process.

Perhaps the biggest lesson for them has been the prime importance of the starting point - the grape.

"The French have a phrase - 'the wine is made in the field'.

"The wine has a certain potential defined by the grapes in the field and… the best you can do is take 100 per cent grapes and make 100 per cent wine. And all wine making is downhill from there," he says.