"This is the special reserve, from this fall's harvest," Cozzaglio announced. "But I'm not satisfied with it." He was standing in the storefront of La Zadruga, the olive-oil company he runs with his wife and partner, Ilaria Galetta, in the tranquil lakefront village of Toscolano-Maderno, a 90-minute drive east of Milan. In his right hand, he cradled a plastic cup half-filled with a liquid whose green glow called to mind an undiluted shot of Czech absinthe. Warmed by the heat of his hand, the oil, still vivid with chlorophyll undegraded by light or oxygen, perfumed the air with the odor of fresh-cut grass.

"Not that there's anything bad about this year's oil," continued Cozzaglio, a modest but intense man who precedes his bolder assertions with a sustained hum. "No defects. But, in my opinion, this year's Villa Romana is at only 70 percent of its potential."

For the third time that weekend, I reminded him that I had come from afar to get a taste of precisely this oil. The same oil that had won the highest possible accolade—three green leaves, denoting "absolute excellence"—in Gambero Rosso's Oli d'Italia, a yearly guidebook published by Italy's leading food and wine magazine that rates upwards of 700 of the nation's best olive oils. The same oil that had been pressed from a cultivar, or variety, of olive that until recently was unknown to modern science. The very oil, in other words, that he seemed determined to withhold from me.

Even before I came to Toscolano-­Maderno, I'd had inklings that Cozzaglio might be a perfectionist. I had mentioned that I was planning to visit La Zadruga to Simona Cognoli, the owner of Oleonauta, one of the few specialty boutiques in Rome or its suburbs to offer an extensive selection of Italian extra-virgin oils. (She's also the author of Olio, an opinionated primer on the subject.) She abruptly dropped her air of cool authority­—on the subject of Cozzaglio, she was willing to gush.

"Sergio is one of the best potatori in Italy," Cognoli said, employing the Italian term for a professional tree pruner. "That makes him an expert at producing the kind of healthy olives that yield the highest-­quality oil. At the same time, his knowledge of the land means he's helping to preserve olive trees that are hundreds of years old." But she warned me that Cozzaglio sometimes took his passion to extremes. If the olives weren't up to his standards, he was even willing to let them rot on the ground, and produce nothing for an entire year. I asked if she'd had a chance to taste Villa Romana. "I did!" she said, her eyes flashing. "Sergio's a virtuoso."

My own interest in olive oil had started not long ago, evolving rapidly into a fixation on best-​­before dates and hard-to-find cultivars. (Similar to apples or wine grapes, European olives are all the same species, but different genetic lines have very different flavors.) Retracing a worthy olive’s trajectory from bottle to grove seemed like the next logical step in my journey, which is what drew my attention to Cozzaglio’s work with little-known varieties. The combination seemed irresistible. The rare and ancient olive trees of northern Italy, prized since the Renaissance for the delicate and subtle flavor of their oil, needed a savior to coax fruit from their long-barren limbs. They found it in Cozzaglio, a kind of Italian Lorax whose passion allowed those trees to speak again.

Now, as I was resigning myself to Cozzaglio’s perfectionism, Galetta came to the rescue. Like someone used to oiling a chronically creaky hinge, she has a knack for mollifying her partner with a simple gesture or well-placed word. As Cozzaglio spoke, she reached for the bottle, and, after pouring out two measures, took a sip from her plastic cup.

"Sergio is right," she said, after doing a strippaggio, the sharp intake of breath between the teeth that coats the taste buds and draw an oil's volatile substances toward the nostrils. "This year's oil might be lacking a little in complex aromas. But the flavors are incredible."

After trading a glance with Cozzaglio—he surrendered with a shrug—I followed Galetta's lead, and commenced with the ritual of swigging, slurping, and pondering. Villa Romana had the qualities I'd come to expect from a top-notch extra virgin: It was velvety, rather than greasy or oily, and imparted the all-important pizzicorino, the peppery catch at the back of the throat. There was something else in the mix, though, that I couldn't quite place.

"You taste it?" Galetta asked, with a note of triumph. "Artichokes, arugula, but also—sardines." She was right. Alongside a pleasant bitterness, I detected the kind of deep flavor I associate with oily fish cooked into a sauce. Villa Romana—even in a year its producer deemed substandard—was like no oil I'd ever tasted before.

Cozzaglio’s love affair with olives began in earnest in 2003, when he founded La Zadruga, whose name refers to the kibbutz-like farmers’ cooperatives common in 19th-century Croatia. (He chose the word thinking he’d be working with several partners, who—uncooperatively—ended up backing out.) He grew up on the shores of Lake Garda, Italy’s largest lake, a staggeringly beautiful microbiome of Mediterranean olive oil in the midst of frost-prone, butter-oriented Lombardy. Though its northern extreme is at the same latitude as Fargo, North Dakota, and the peaks of the surrounding Dolomites are snowcapped in winter, Garda’s shores are studded with lemon and palm trees. Olive orchards, which climb the hillsides that surround the lake to heights of 1,500 feet, are everywhere. It is the northernmost point in the world where olives can be reliably cultivated.

We had driven to a grove adjoining a stretch of public beachfront in Toscolano-Maderno. “My family always owned olive trees,” he told me as we walked amid the time-twisted century-old trunks, “but we never had a farm. My grandfather used to make olive oil, but only for our own use.”

Cozzaglio trained to be an electrician but found he hated the job—rewiring homes made him nervous. To find relief from the stress of work, he rode mountain bikes or went for long hikes. One day, while trekking in the mountains, he had a simple thought: Instead of earning a living inside other people’s homes so he could be outside on the weekend, why not find a way to work outdoors every day of the week?

He began working as a potatore, eventually signing contracts with the local commune to tend orchards on public property. Locals who had trees on private lots but no time to care for them allowed him to harvest their olives in exchange for some of the oil. Because he owns no trees of his own, Cozzaglio is, in essence, a gleaner—a collector of unused crops—albeit a professional one, with the contractual right to harvest local olives. It is challenging, sometimes exhausting work, particularly during the harvest period from October to December.

It turned out Cozzaglio had a talent for pruning. In 2012, he participated in Italy’s annual olive-tree­-pruning contest. Sixty competitors had come to Ascoli Piceno, in the Marche region, from every corner of the country and were given half an hour each to prune three midsize trees. Cozzaglio did so faster and more skillfully than anyone else in the field, winning the title of the nation’s best potatore. “The important thing,” Cozzaglio explained, “is to learn to cut the right branches—not too many—and do it fast. Compared with my competitors, who often learned bad techniques from their parents or grandparents, I had the advantage of having no preconceptions.”

On Toscolano-Maderno’s beachfront, he showed me two of the tools of his trade: a long-handled ripsaw with a curved, serrated blade, and a pair of telescopic shears. Cinching a black-and-red bandanna around his head, he went to work on the upper branches of a tree that bore a few Casaliva olives, one of the region’s best-known cultivars, shriveled and black at this late point in the season. Soon Cozzaglio was doing a quick shuffle around the trunk until the grass at our feet bore a tangle of succhioni, or suckers, the shoots that grow out of upper branches and must be trimmed so a tree can bear new fruit. When he let me try, it took me minutes of hacking and muttering to achieve what Cozzaglio had done in seconds.

If Cozzaglio was an efficient pruner, he also proved to be a talented oil-maker. He would start gathering olives in October—just as they began to change from green to black—at eight in the morning, using a hydraulic wand with vibrating fingers that sent the fruit tumbling from the branches onto mats on the ground. (The work, much of which is done on ladders, can be dangerous. An olive gatherer in the Lake Garda region is killed in a fall almost every year.) Harvesting had to be completed by four in the afternoon, so, to ensure absolute freshness, the olives could be pressed by the end of the day.

For generations, olives were crushed under massive stone mill wheels, many of which are now on display on the region’s roadsides. The cloudy oil that emerged was typically mild in flavor because this slow pressing exposed it to oxygen, which mutes the bracing bitterness and pepperiness of a cleanly pressed oil.

Cozzaglio was convinced of the advantages of using the latest technology, in which olives crushed by stainless-steel grinders produce a paste that is then whirled in a centrifuge, yielding a clear oil that expresses the intense flavors of the fruit. After a decade’s experimenting with half a dozen local mills, he’d settled on Domus Olivae, a modern facility in Riva di Garda. The only drawback was its location at the northern tip of the lake, a 30-mile drive from the groves Cozzaglio tends.

One evening I rode shotgun with Galetta at the wheel of their stick-shift Fiat, a hair-raising drive through blind curves and narrow lakeside tunnels. “I love to drive,” Galetta said, as she deftly swerved in and out of oncoming traffic to pass a slow-moving German tour bus. “And it pleases me to help Sergio do what he loves.” From the back seat, Cozzaglio admitted: “I’m a good potatore. I’m a good oil-maker. But I’m not a good seller.”

In addition to making the daily run to the mill, Galetta takes care of packaging, designing the bottles, and packing them in boxes of handmade paper. In 2015, their labels began to show up on the shelves of leading specialty boutiques in Milan, Bologna, and Rome, and La Zadruga won its first awards.

Cozzaglio’s apprenticeship happened to coincide with a growing appreciation for monocultivar olive oils—made with a single ­olive variety, rather than a blend. In Spain, France, and Greece, a few star cultivars dominate production, but Italy, with its multiplicity of soils and microclimates, has always been the Ama­zon rainforest of olive bio­diversity. At last count, there were 530 distinct olive varieties in Italy.

“Now there are 531,” Cozzaglio said, with a tone of triumph, as he plucked a roundish olive from a silver-leafed tree. Slicing it open with his olivewood-handled Opinel knife, he revealed cherry-red flesh clinging to an unusually circular pit.

We had returned to the Toscolano-Maderno lakefront and were wandering amid the ruins of the sprawling residence of the Nonni Arrii, as the upper-class Roman family who lived here 2,000 years ago were known. Before he started to tend trees at this site, Cozzaglio had already done meticulous research in the region. Local farmers, some in their 90s, recalled a time, before the Second World War, when they’d harvested two since-­forgotten olive varieties on the hills around the lake.

Cozzaglio found specimens of the long-lost Miniol and Negrel trees on private land, and coaxed the abandoned trees into bearing enough fruit to add to his line of monocultivar olive oils. Not even the old-timers, though, could tell him the name of the oddly shaped olive trees that grew alongside the well-­preserved mosaic floors of the Roman villa by the lake.

On a hunch, he sent samples of branches to the National Research Council’s Institute of Biosciences in Perugia. After a year and a half of analyzing the DNA, two weeks before I arrived, the lab confirmed what Cozzaglio suspected: Villa Romana, as the olive would henceforth be called, was an unknown, possibly very ancient cultivar, one that had never appeared in any official catalog.

I asked him whether it was possible the tree we were looking at could date back to Roman times. “Not this exact tree,” he said. “There was a great frost here in the early 18th century. Even the lake froze. Everything died.” But the roots of olive trees, Cozzaglio pointed out, are extremely resistant to cold, which means they can send up new shoots even after the wood has died. It was well-known that the Romans kept olive trees on their rural estates, using the oil to fill lamps, soften their skin, and feed the household. The Villa Romana variety’s genetic profile suggested we were looking at a descendant of trees that stood here in the first century. Amphorae with residue from classical times survive, but the centuries have done their work, making it impossible to know what the oil they once contained was actually like. Bringing lost varieties back to life might be the closest we can come to tasting ancient oil.

Cozzaglio had turned his back to me, and was dreamily caressing the branch of a small tree with some tiny olives on its lower branches. “I don’t know what variety this is,” he said. “Six years ago, when I discovered it, it was a bush, it was nothing.” After several seasons of careful tending, it had started to flower and bear fruit. “Now it’s grown into a tree. This is the part of my work I love. To help give birth to a plant.” It might prove to be another ­unknown cultivar, ​Cozzaglio’s next discovery.

That night, at a farewell dinner at a nearby seafood restaurant, Cozzaglio and Galetti politely asked the owner if we could use the olive oil they'd brought to season our grilled scallops, branzino, and scampi. Under lashings of bitter, peppery Miniol and smooth, grassy Leccino, the seafood sprang to life. The owner, intrigued, asked if he could share some with his other clients. We watched as diners at the ­tables around us sipped, smiled, and nodded appreciatively. A few coughed as the Miniol bit into the back of their throat but, one by one, they all turned to Cozzaglio with congratulations: "Complimenti!" He replied to the praise with the humility befitting a potatore: "Please, please," he said, "save your compliments for the trees."