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Is that grapevine Cabernet or Zinfandel? Hint: look at the leaves.

Have you ever driven by or walked through a vineyard and wondered what variety of grapevine you were looking at? It’s a question California wine grape growers get all the time: “How do you tell one grape variety from another?”

Of course in late summer and early fall before harvest, when the grapes are hanging on the vine almost ready to pick, it’s easy to tell if it’s a white or red variety. But if the grapes are red, say, how can you tell whether it’s Zinfandel or Cabernet Sauvignon?

“The simplest way to identify the variety is to first take a look at the leaves,” says Kurt Kautz, controller at Kautz Family Vineyards, which farms over 3,000 acres in the Lodi and SierraFoothills regions. “Some varieties, particularly the major ones like Chardonnay, Cabernet Sauvignon and Zinfandel, have very distinctive leaf types.”

These distinctions have to do with the shape of the leaves, the edges (whether they’re smooth or jagged), and the depth of what’s called the “sinus” (the space between the leaf lobes). For instance Chardonnay leaves have only slightly indented sinuses while those on Cabernet Sauvignon leaves are much more pronounced.

Another way to tell varieties apart is by cluster size and shape. “Some varieties have big clusters, like Zinfandel and Merlot,” says Kautz (who points out that growers always know what they’re planting because nurseries selling grapevine stock must provide legal certification as to the varietal). “Cabernet Sauvignon clusters tend to be smaller and more compact.”

Still, as Kautz notes, different growing regions – with different soils and micro-climates – as well as different viticultural practices can result in varying grape sizes and cluster shapes. Zinfandel clusters on a vine in Paso Robles may look somewhat different than clusters in Amador County, for example.

While identifying grape vines might seem like a guessing game, it has actually been formalized into a science known as ampelography. In the 1940’s Professor Pierre Galet, chair of the viticulture department at one of France’s top viticultural schools, created a system which classifies grapevine varieties based on a number of factors including the shapes and contours of the leaves, the shape of the clusters, characteristics of the growing shoots, and the color, size, flavor and seediness of the grapes.

While most California wine grape growers study ampelography in school, hands on experience in the vineyard is really the only way to get good at identifying wine grape varieties. And even then, different clones – sub-groups of varieties – can be impossible to identify through the naked eye, and lesser known varieties – say Rousanne or Viognier – can be difficult as well.

Today, in addition to the ampelography system created by Professor Galet, scientists at the Univeristy of California, Davis – most notably Dr. Carole Meredith – have pioneered the use of genetic fingerprinting to identify grapevines. DNA analysis has helped some wine grape growers identify their own grapevines (for instance if they have a vineyard with vines planted many decades ago), and has even been used to trace the ancient origins of grapes such as Zinfandel and Sangiovese.

Though identifying wine grape varietals is probably best left to the experts, consumers of California wine can always be sure that the varietal of wine they buy is the varietal they get. “California is highly regulated when it comes to truth in labeling,” says Kautz. “Consumers can definitely trust in the varietal integrity of California wine.”

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“The simplest way to identify the variety is to first take a look at the leaves,” says Kurt Kautz of Kautz Family Vineyards.


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