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.