Lose control of your shopping cart in a grocery store's wine department and it's apt to collide with a shelf of old-vine zinfandels.

Old-vine riesling? Not nearly as likely.

You have to wonder how so many older zinfandel vineyards survived, given both zinfandel's unsteady history and California's spreading urbanism.

It helps that there's no federally enforced definition of "old vine," as there is with many terms on wine labels. Depending on the perspective and the marketing acumen of a vintner, an "old vine" can be just 10 years old, though more California winemakers seem to concur that for a vine to be considered old it must have been around at least 50 years.

Scott Harvey, a Napa Valley winemaker who also makes wines with grapes from Amador and Mendocino counties, knows both old-vine zinfandel and old-vine riesling. The lineup of his eponymous brand includes a proprietary wine called Vineyard 1869, which takes its name from what is believed to be the oldest zinfandel vineyard in the country, up in Amador County's Shenandoah Valley.

And under the brand that carries his wife's name, Jana, he makes an old-vine riesling from Mendocino County.

With the two varieties, he applies different standards to define "old vine." By his reasoning, a zinfandel vineyard must be at least 50 years old to qualify for the designation. A riesling vineyard, on the other hand, need be just 35 years old. His reasoning: There just aren't any riesling vineyards in California much older, or at least he hasn't found any. Indeed, little riesling is planted in the state at all.

Regardless of whether an older vineyard is zinfandel or riesling, it intrigues Harvey largely because the roots of the vines have had time to creep deep into the soil, 25 feet or so. The roots of younger vines, by comparison, may descend only around 6 feet. In wet years, the shallow roots of younger vines sit in damp soil, their grapes swelling with water, thinning the character of the wine they ultimately yield, explains Harvey. In contrast, rainfall from even a particularly wet winter won't soak the longer roots of older vines, giving them an advantage in producing more consistent and mature crops.

In a dry year, on the other hand, younger vines don't get enough nourishing moisture, potentially stunting growth of the grapes, whereby the longer roots of older vines can tap into deeper supplies of moisture, Harvey said.

He also maintains that the deeper the roots go, the more they penetrate through varied types of soil, helping yield a more complex wine. "I always say a young vineyard is more mono-dimensional while the old-vine vineyard is more multidimensional."

His perspective looks to be at work in his Jana Winery 2009 Mendocino Old Vine Riesling, a subtly layered and classically structured interpretation of the varietal. The wine is medium-bodied, with refreshing suggestions of tropical fruits, apples, peaches and pears. The small amount of residual sugar intensifies the wine's fruitiness rather than leaving it tasting sticky sweet. The finish is crisp.

By California standards, the Jana qualifies as an older riesling on the market, but that additional time in bottle has rounded out the wine, leaving it an unusually balanced and seamless take on the varietal.

Riesling isn't an easy wine to make, but Harvey's winemaking education was enhanced by studies in Germany, where riesling reigns. While growing up in the Sierra foothills, he got introduced to Germany as a high school exchange student in the Rhineland Pfalz region. He later returned to Germany to study enology at Weinbau Schule in Neustadt and to apprentice at K. Fitz-Ritter Winery. Back in the United States, he's made rieslings with grapes from Michigan and New York as well as California.

The key to seizing the attributes he wants in riesling is to harvest the grapes at just the right sugar level, capturing both the direct fruit and crisp acidity that distinguishes well-balanced and flavorful riesling. Most of the fruit in this riesling is from Greg Nelson's vineyard in a small sheltered valley along the Russian River just south of Ukiah. Nelson planted the vineyard in 1974.

The window of opportunity for picking the grapes at the sugar level Harvey prefers generally is only about a week. Pick the fruit just a couple of days late and the resulting wine won't say "riesling" with any clarity.

"It will be just white wine," Harvey said. The minerality and terpenes he craves will be lacking. (Terpenes are flavor compounds credited largely for riesling's floral attributes.)

The wine includes about 9 percent riesling from a vineyard in the Rutherford area of Napa Valley, which he feels bolsters the wine's minerality.

Jana Winery 2009 Mendocino Old Vine Riesling

By the numbers: 9.5 percent alcohol, 0.8 percent residual sugar, 417 cases, $22.

Context: Scott and Jana Harvey pair the riesling with dishes "that have some zest," such as lemon chicken, but they also feel it has the structure and fruit to stand up to dishes with some spice, such as pasta in a puttanesca sauce.

Availability: In the Sacramento area, the riesling is stocked by Plaza Foods at Rancho Murieta and by Lake Forest Wines in El Dorado Hills and Folsom. It also can be ordered online at www.scottharveywines.com.

More information: The winery's tasting room is in the Sierra foothills, at 79 Main St., Sutter Creek, open 11 a.m.-5 p.m. Thursday through Monday.

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