California's vineyards: the road movie

We started filming the new Oz and James's Big Wine Adventure on Muscle Beach at Santa Monica. Why? What's that got to do with wine? Well, that's where I won the world wine-tasting championship – a long, long time ago. On the beach. In the bright sunshine, with the sea breeze blowing sand into our Chardonnay and the rippling pecs creating more than a minor diversion for some of the contestants.

It just said it all to me about the mad, self-indulgent genius of California, the Golden West. I probably won because ever since I was a kid I haven't been able to spy a beach without longing to strip down to my bathers and leap in to the surf. Nowadays, I bury a bottle of white up to its neck in the moist cool sand above the water line and sup it as I dry off and warm up again after churning about in the waves. Sea salt, sand and Sauvignon Blanc. I could still blind taste it in a line-up, with the brine running out of my nose into the glass.

So that's where we started the filming. James wanted to re-title it Oz and James's Thinly Disguised Drinking Holiday, but I was determined to make him learn something – about California wine, about grape varieties, about the differences between Old World and New World wine styles. However, since he has the attention span of a gnat when it comes to wine and frequently seems only concerned with how quickly I can open the bottle and how swiftly he can drain it, I needed to include all the other parts of California life I could think of – many of them with a rather tenuous connection to wine, I must admit – just to keep him alert and sober. Alert enough to bray endlessly – "What's this got to with wine? Will it help me find a decent bottle at my corner shop for a fiver?"

Well, probably not. In most wine-producing cultures there's a bottom, a middle and a top. The bottom is either graceless, anonymous plonk or heavily promoted – and heavily discounted – brands. The middle is where the wine gets interesting. It's still affordable – say £5 to £10 – but you get enjoyable differences between different grape varieties, regions and winemakers' attitudes and ambitions. The top ranges from excellent, rare, individualistic wines worth a high price, to self-important, overhyped behemoths to be avoided at all costs – especially if you are the one likely to be picking up the tab, because you can be talking anywhere between £20 and several hundred pounds, sometimes even a thousand or more per bottle. Please, as James would say, as he greedily sluices the stuff down his throat, it's only a bottle of wine.

Well, California does have a successful bottom end. Whether it's Fred Franzia and his "Two Buck Chuck" Merlots and Chardonnays or the big brands such as E & J Gallo. It also has a vibrant, throbbing top end – an absolute queue of rich people wanting to be vineyard owners and winemakers, as well as a healthy brood of less-well-heeled but passionate men and women who believe in California's ability to make great wine, and who can produce it – but it won't be cheap. Yet the middle, the interesting and affordable, is amazingly and dispiritingly lacking. Ravenswood and its chewy tasty Zinfandels do appear in Britain (Waitrose and Wine Rack do them). Bear Creek, a Marks and Spencer exclusive, is pretty good. Marmesa is a Syrah and Chardonnay pair of excellent quality that Oddbins has just taken on. But apart from these, hardly a whisper. So I don't blame James for complaining about good affordable wines – but it did mean that I had to keep his mind occupied.

To start with, we had a 42ft mobile home to manoeuvre around. This is longer than a Routemaster bus. I wouldn't be allowed near the wheel of such a beast in Britain, but in California there's a cursory and largely incomprehensible familiarisation ritual and off you go. Terrifying – but it kept James amused and challenged. And that was just the driving. Living in it presented a different set of challenges. Two blokes with a pretty disparate view on things like – who gets the bed? There's only one. Do you shave before you shower, or shower before you shave? Do you wander around in the buff despite not really knowing each other or do you skulk furtively in corners wrapped in towel and dressing-gown? Does the air-con keep you awake? But if we turn it off, we boil. Do you demand Cap'* Crunch and Yorkshire Tea for breakfast – every day. I mean, these become major matters when you're stuck inside what resembles a suburban semi on wheels, especially when it's decked out in a dozen shades of sepia, guaranteed to keep your spirits up.

Luckily, the scenery in California is always interesting, sometimes spectacular, and if you can't stop off in a vineyard, the mobile home parks are positively swish (with the exception of Calistoga in the Napa Valley which was more like a poorly asphalted municipal car park). If I had to choose favourites, I'd choose the urbane Flying Flags site in Buellton, Santa Barbara County, right next to the motel where Sideways' shenanigans were filmed, and the Mount Madonna operation on Hecker Pass in Santa Clara County, which is set in the depths of an ancient forest.

The battle facing good wine producers in California is similar from the south to the north of the state. Most of California would be desert without human ingenuity. But offshore, the ice-cold Alaska current lurks. This produces awesome fog banks that rise to apocalyptic heights and which are dragged inland through river valleys and cracks in the coastal mountain range. Many vineyard areas, such as the Salinas Valley in Monterey, Santa Maria in Santa Barbara and Carneros north of San Francisco, can be cloaked in fog until midday. Which keeps the vineyards nice and cool all morning.

Eventually, the sun burns the fog off and the vineyard temperature soars. But the hotter it gets inland, the more the air rises, creating a vacuum that can only be filled by dragging in air from the sea. Once again, the Alaska current plays its part, because the icy seas create icy air and this is sucked inland in the afternoons – once again cooling the vines, keeping the fruit flavours fresh. Without this daily routine of fog and cold winds, fine wine would be impossible to make in California.

We drove from Santa Monica up to Sonoma and Napa, north of San Francisco. We did make some forays inland, sometimes for wine, sometimes not. We went over the bleached, barren hills of the San Benito range to check out Modesto, where the Gallo company headquarters presides over a wine harvest as big as that of the whole of Portugal, and where Fred Franzia runs his billion-dollar empire of cheap wine out of a portable cabin. We headed inland from Paso Robles to see the spot where James Dean, the rebel without an airbag, met his maker by dint of a head-on with a fellow called Turnupseed.

But mostly we stuck close to the sea. Santa Barbara is a cool, attractive resort town spread along the warm-water beaches below Point Concepcion. North of Point Concepcion you bathe in a wetsuit or keep checking that you can still feel your fingers and toes, and if you can't, get out quickly – it's that cold. You can take Route 101 – a broad freeway that takes the easy valley floor northwards and passes through the vineyards of Paso Robles and the Salinas Valley of Monterey – but then you'd miss Route 1, one of the great seaside, cliffside, American roads. The signs said no vehicles longer than 32 feet should attempt the drive. Oh yeah?

Route 1 clings to the cliffs and the Santa Lucia Range high above the sea, then sweeps across the broad mouth of the Salinas Valley and round into Santa Cruz, a joyously downmarket seaside resort with a great boardwalk and funfair. We did stuff on dodgems that adults shouldn't be allowed to do. Since you're on Route 1, you might as well take it right up to San Francisco, but the mountains of Santa Cruz are densely wooded and alluring. Small roads criss-cross them. Not advisable in a mobile manor house, but delightful in a car or on a motorbike.

You must spend time in San Francisco to see why people describe it as one of the world's most liveable cities. And you must leave San Francisco the right way – over the Golden Gate Bridge. If it's buffeted by swirling fog – it often is – your crossing will be eerie and unsettling. If the sun is out, this majestic, two-mile, rust-coloured span makes your heartbeat race with awe and excitement.

We based ourselves north of San Francisco Bay at Calistoga, at the head of the Napa Valley, which allowed us to roam through both the Sonoma and Napa Valleys – both packed with vineyards and wineries, but the Sonoma Valley is more human, more varied and less self-obsessed. Wineries litter the landscape in both valleys, many offering tastings – but have some loose change ready. I turned up at Opus One winery and they wanted $25 (£12) for a single taste of a single wine. What did I say? Loose change? Make that $10 bills. Restaurants are everywhere, too. Some, like the Auberge du Soleil and the French Laundry, world renowned. But others did me just as well. Babes Burgers at Schellville in southern Sonoma. Las Vacas Tacqueria – a Mexican joint opposite the glitz and glamour of Opus One in Oakville, Napa Valley. The Home Plate Diner a mile north of Calistoga on Route 29 or the Bear Republic Brewpub just off the square in Sonoma's Healdsburg. These are all relaxing, reviving hangouts to remind you that Napa and Sonoma aren't solely about wine, about the glitz and the high life.

There's another world there, and it makes the wine taste much better when you've sampled it.

Further viewing and reading: 'Oz and James's Big Wine Adventure' starts this Tuesday, 8pm, on BBC2. 'Oz Clarke's Wine Atlas: Wine and Wine Regions of the World' is published by Anova Books, £40