(Vogue) - From Paris to Tokyo to Copenhagen to Brooklyn, wines made with little to no chemical intervention—so-called natural wines—are the toast of the cognoscenti.

Large, wet snowflakes started to fall just as I left Paris, and by the time the car rolled through the medieval city of Blois, with its sharp spires, the whole of the Loire Valley wore a cloak of fog. I continued southward, past châteaus that looked like vague phantoms, or were those merely trees huddling in the gloom? Pierre Jancou, the conjurer of a succession of enormously popular Paris restaurants and wine bars—La Crèmerie, Racines, Vivant, Heimat, and a new project percolating on the Rue Servan as he recovers from a broken leg—had sent me here, explaining that if I wanted to understand natural wine, I’d need to visit Claude Courtois and his son Etienne.

For lovers of natural wine—which, though its definition is contested, might most simply be described as fermented grape juice with nothing added or removed in the making of it—Courtois’s vineyard in Soings-en-Sologne is holy territory. The man himself embodies an agrarian ideal, the ascetic farmer-vintner who devotes every day of the year to his vines or his cellar, a man with scant curiosity about who is drinking what in the Paris bars, whose only commercial ambition is to feed his family. Jancou first tasted a Courtois vintage in 2002, and it was a sort of epiphany. (Natural-wine people always remember their conversion moment.) “Here was a wine that was so alive, so energetic, that was made with such love,” he remembers. “After that there was no going back.”

If you have been to dinner in Copenhagen or Tokyo or Brooklyn or Montreal in the last few years, then you have probably drunk wines made with little to no chemical manipulation. The bottle arrives; maybe it has a funny name like You Are So Happy, a pét-nat (pétillant naturel, a naturally sparkling wine) from the Loire that I was served in Paris at Le Chateaubriand. In the glass, perhaps it looks a little thin, a little murky because it is unfiltered, a little brown due to oxidation; perhaps it fizzes unexpectedly or gives off a cidery funk. If you’re counting on something familiar, maybe you’re disappointed. “It’s like in the theater, when you break the fourth wall,” says Alice Feiring, a natural-wine maven whose new book, her third, is about the millennia-old winemaking tradition of Georgia. “Natural wine comes out and greets you. It can be fun or serious. It can taste like good, old-fashioned wine or not, but it has a certain frankness.” Like tomatoes in August, natural wine tastes of itself; it is in a sense a fresh product, its internal life not stalled by chemicals in the field or additives in the bottle. As a result, these wines are often thrilling to drink, fascinating and expressive, but they refuse to deliver a controlled experience, instead speaking loudest to those who enjoy the feeling of surprise at the table.

I was greeted at Les Cailloux du Paradis, the Courtois vineyard, by Paradis himself, a Labrador retriever the color of the golden hunks of quartz that poke through the soil here and there and lend a flintiness to the wines. Etienne followed; with a wild nest of black hair, wearing a fleece decimated by moths and mud-caked cargo pants, he was doing his insufficient best to hide a handsomeness much sighed over in natural-wine circles. Dog and winemaker led me into a small farmhouse, where we were joined by Claude, who snipped a sausage hanging by a string from the rafters and handed it to me along with a paring knife. “You’ll need energy,” he said, adding to my kit a Che Guevara flat cap and a pair of muck boots.

The vineyard, in the February mud, wasn’t much to look at. The vines had been pruned back tightly, the gray soil churned by earthworms and dotted with lamb’s lettuce. Claude, whose grandparents on both sides were Burgundian winemakers, planted the first rows of gamay and romorantin, a beloved local grape, 50 years ago. “I was born to do this,” he told me, “and I learned in the old way. After the war, chemistry came to the vineyards, and now most wine in France, all over the world, is poison, undrinkable. It tastes of the things added to it and not the grapes, not the ground. Maybe I’m too fragile. I can only eat food and drink wine that is clean. No doping. No Lance Armstrong stuff here.”

A cynic might say that Claude’s far-left position is one he can afford to take. Making wine naturally, with no chemical protectors along the way, is a high-wire act. You can lose an entire vintage to a nasty bacterium or a wayward fermentation. But in the Loire land is cheap, or at least cheaper than in Burgundy or Bordeaux, and his vineyard is small, so if the worst happened, he’d survive. The first growths of Bordeaux, on the other hand, have investors to appease and customers who expect a very specific product. Though in France big wine and natural wine exist more or less harmoniously, the issue can be polarizing. Those who drink natural wine rarely drink anything else. And those who scorn it do so with vitriol. Robert Parker, the world’s most influential wine critic, has called natural wine a sham, a fraud, “vinofreakism.” Other critics dismiss the wines as the stuff that unwashed hippies make for 22-year-olds with neck tattoos; they call them characterless at best, putrid at worst. A few years ago, all the winemakers of Burgundy were ordered to spray pesticides to prevent a disease called golden rot, and when the lone winemaker who refused finally won a protracted court battle, he was a hero in natural-wine circles—not in Burgundy, where a plague on his vineyard could have threatened hectares of priceless old grapes.