vines at night

Warm Days, Cool Nights: 2012 Off to a ‘Normal’ Start

Now that fruit has set, following and documenting the  development of grapes and vines (a study known as phenology) begins. The overall goal for growers between now and veraison is to allow enough light and airflow through the canopy to begin developing flavors and tannin in the skins of the grapes while also protecting the fruit from mildew, botyritis and sunburn. And, as one vineyard manager points out: “Grapes don’t recognize weekends, holidays, and never ever take a day off!”

Fortunately, the year is off to a warm, dry start: “2012 is shaping up to be a sharp contrast from the previous two vintages. We are now past bloom and have avoided any of the devastating, crop-limiting rains we have seen in previous years. Clusters are noticeably larger and berries have developed much more evenly than 2011,” says Chuck Mansfield of Hop Kiln Winery in the Russian River Valley.

If there were a way to quantify “warm,” Jon Ruel, Director of Viticulture & Winemaking for Trefethen Family Vineyards and a member of the Napa Valley Grapegrowers has it.  By measuring cumulative degree days, he creates a “warmth index” for the vineyard. According to his calculations, April and May in Oak Knoll were right around the long-term average of 560. “That said, we haven’t seen anything at or over 560 since 2004,” says Ruel. “So, it feels great to have a ‘normal’ start again!” Already, growers are trying to anticipate when harvest will be: “The soil moisture is already being used up and vine foliage growth has begun to slow down. This suggests to me that fruit ripening, and thus harvest, will be earlier than they have been for the last few years.”

The diurnal shift, that annoying and sometimes extreme temperature swing that makes it nearly impossible to know what to wear (may we recommend keeping a cashmere sweater in your purse at all times) is also what makes Napa Valley “such a special place to grow grapes.” “This past Monday,” says Ruel, “we saw an impressive 55-degree temperature swing with a low of 42 degrees F in the morning and a high of 97 degrees F that afternoon.” Impressive indeed.

At this stage of fruit development, growers talk about the size of individual berries and clusters, the space within those clusters and begin to estimate ultimate yield. “Despite a few windy days and a little threat of rain on June 4th (which turned out to be nothing), we made it through bloom and set looks pretty good so far,” says Kevin Skene, owner of Skene Viticulture, Managing Partner of Redwood Glen Vineyard in Dry Creek Valley and a licenced PCA. “Crop size appears to be about average in most spots, a little light in some ranches, but overall looks pretty good. At least we have more fruit than last year!”

Skene also provided us with a very thorough and detailed phenology report, in which he introduces us to some very technical grape-size terminology: Peas and BBs.

In the Russian River Valley, chardonnay and pinot noir grapes in warmer areas are pea-size with clusters expected to close in about 7-10 days. In cooler areas, Skene is seeing BB-size berries, with bunch close expected in 2-3 weeks. Sauvignon blanc is lagging slightly with some berries in cooler regions still going through set. Zinfandel and syrah vines have BB- to pea-size berries in the warmer spots and BB-size berries in the cooler areas.

In Dry Creek Valley, chardonnay clusters are starting to close with pea-size berries. Zinfandel and merlot grapes are coming along with bb- to pea-size berries with zinfandel bunches expected to close in about 10-14 days depending on aspect. The sauvignons — blanc and cabernet — are still at the BB-stage.

In the south end of the Alexander Valley, chardonnay grapes are about on par with those in Dry Creek Valley: berries are pea-size and bunches will be closing soon. Merlot, cabernet sauvignon and sauvignon blanc are still mere BBs.