Jordan winemaker Rob Davis inspects a barrel of the 2016 cabernet sauvignon blend. Jordan Vineyards & Winery has tweaked the style of its popular cabernet sauvignon, moving toward using French oak barrels exclusively. (Dave McIntyre)

Most people with a successful product don’t want to fiddle with the formula. Why fix what “ain’t broke,” after all?

That didn’t stop John Jordan and Rob Davis from tweaking their popular cabernet sauvignon at Jordan Vineyard & Winery in Sonoma County’s Alexander Valley. Davis has been the winemaker at Jordan since Tom and Sally Jordan, John’s parents, founded the winery in 1972. For three decades, he made cabernet that was a sort of Franco-American mash-up of styles. Tom Jordan loved bordeaux, and wanted to produce wine in the French style. But it was a Napa Valley cabernet — the Georges de Latour Private Reserve from Beaulieu Vineyards — that convinced him quality cab could be made in California.

The Georges de Latour was aged in 100 percent American oak, so Tom Jordan decided his cabernet would split the difference: half aged in French barrels, the rest in American. And he hired BV’s celebrated winemaker André Tchelistcheff as a consultant.

The formula worked, and Jordan’s cabernet became a standard-bearer for California in general, and Sonoma’s Alexander Valley in particular. They kept to the French style, maintaining alcohol levels under 14 percent when California cabs crept up to 15 percent and higher.

But when John Jordan took over the winery in 2006, he and Davis decided they needed to up their game. The estate vineyard was producing inconsistent quantity vintage to vintage, and the wines had some underripe “green” flavors of bell peppers. So Jordan and Davis began purchasing cabernet grapes from farther up the valley, closer to Geyserville, as well as smaller amounts in Dry Creek Valley and Mendocino County. Today, the only grapes they use from the original Jordan vineyard come from a block of petit verdot vines that performed consistently well over the years.

Over time, they realized the fruit they were purchasing interacted differently with the French and American oak barrels. The new fruit had riper tannins and not so much of the green flavors.

“American oak is aggressive and has a large impact on the wine,” Davis told me when I visited the winery recently. “It adds coconut and dill flavors, which can mask underripe, vegetal flavors in the wine.”

“Tannin isn’t a taste. It’s a feel,” he said. “The French oak tannins bond with the tannins in the fruit to make a longer tannin molecule, creating a velvety texture in your mouth.”

The key, Davis said, is the wine’s finish — the impression it leaves on your palate as the flavor fades. “The finish is the memory of the wine. If the finish is rough and bitter, that’s what you remember. French oak knits the fruit together, orchestrating the flavor statement so it is round and soft, and the finish is supple.”

Such realizations don’t come quickly. When Davis persuaded John Jordan to source grapes from other growers, it took a few years to negotiate long-term contracts and secure reliable sources of fruit. Davis had already increased the percentage of French oak he used in blending the flagship cabernet sauvignon. But the epiphany didn’t happen until early 2015 when trial blends of the 2013, already in barrel for a year, showed the wine tasted better when only French oak barrels were used.

“Hands down, the finish was longer and the wine was better,” Davis recalls. So with the 2015 vintage, Jordan’s cabernet sauvignon is aged exclusively in French oak.

“With the improvement in our fruit sourcing, it would be a shame to mask such wonderful fruit with American oak,” John Jordan explained in an email. “Jordan has always striven to deliver value to our customers, and moving to 100 percent French oak is the culmination of a 10-year effort to improve the quality of our wine.”

By abandoning the estate wine model and the 50-50 oak regimen, he and Davis have moved closer to Tom Jordan’s original ideal of producing a Bordeaux-style wine in California.

The decision to go all French oak is costly. French oak barrels cost at least double the price of American oak, but John Jordan decided to keep the cabernet’s price steady at about $55 a bottle.

We won’t be able to buy that 2015 for another two years, however: That 2013 vintage, with 83 percent aged in French oak, is the current release.

Davis poured me a sample of the 2016 cabernet from a barrel manufactured by Nadalié, a French barrel maker. The wine was lovely — supple and long, with a velvety texture. It had been in barrel since December and will remain there for 12 months. Early next year it will be blended, then bottled in the summer before being released to the market two years later.

Davis opened a few older bottles for me to try. The 2012 has bright fruit and impeccable balance; Davis said it was his favorite of recent vintages. But the 2003 and 2002 had aged gracefully, showing some of the aggressive woodsy characteristics of American oak, perhaps, but also some delicious, elegant fruit.

Those wines were worth waiting for. And the new cabernets will be worth waiting for too, as one of California’s favorite wines keeps getting better.