Winegrape Varieties That Can Beat The Heat

Winegrape Varieties That Can Beat The Heat

This is one of the most promising red winegrapes for California's San Joaquin Valley, a clone of Teroldego. (Photo credit: Lindsay Jordan, UCCE)

This is one of the most promising red winegrapes for California’s San Joaquin Valley, a clone of Teroldego. (Photo credit: Lindsay Jordan, UCCE)

Within California, a select few grape varieties dominate the wine market. According to the California Department of Food and Agriculture’s “2015 Grape Crush Report,” only nine varieties accounted for almost 75% of all the grapes destined for wine production in California.

Just the top two varieties, ‘Chardonnay’ and ‘Cabernet Sauvignon,’ accounted for more than 28% of the total crush. While these top varieties may be widely planted throughout the state, their fruit and wine quality can vary dramatically by wine growing region.

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About 50% of the winegrape acreage in California is found in the San Joaquin Valley (SJV), an important agricultural region with a long and rich
viticultural history.

Using a technique developed by A.J. Winkler and Maynard Amerine at University of California, Davis, wine-growing regions can be categorized by their heat summation units over the growing season. The SJV is undeniably categorized as a Region V, the warmest of the wine-growing region classifications and warmer than the other wine regions within California.

High Number of Degree Days
The central SJV has accumulated greater than 4,500 degree days in each of the last four years, well exceeding the minimum threshold of 4,001 degree days for a Region V classification.

Region V climates can create challenges to quality wine production goals. High temperatures hasten the metabolism of organic acids, which can result in fruit with undesirably low acidity. High temperatures can also suppress anthocyanin biosynthesis and promote anthocyanin degradation in the berries of many traditional red wine varieties, thus resulting in suboptimal wine color.

For economic viability in the SJV, grape growers must aim to maximize production while reaching certain ripeness parameters. Yet when meeting high tonnage demands, some fruit quality issues may be exacerbated by the fact that the most popular and widely grown wine varieties were selected to ripen under much dramatically cooler climatic conditions.

By selecting grape varieties that can innately produce superior fruit in the heat of the SJV, some of the wine quality issues associated with warm climate wine production may be alleviated. With more consumers seeking out distinctive wines and with the dramatic rise in the popularity of blended wines, winemakers have more opportunities to use fruit from unfamiliar grape varieties to improve wine color, aroma, and flavor when crafting their products.

The number of certified grape varieties from Foundation Plant Services (FPS) at UC-Davis gathered from international collections only continues to grow, including an ever-increasing number of grape varieties that originate from warm climates, like Spain, Portugal, Italy, southern France, and Greece. Grape varieties from regions like these may be better adapted for grape production in the SJV.

Potential Of Other Varieties
Recognizing the need to evaluate the performance of alternative varietals in the SJV, the now retired University of California Cooperative Extension (UCCE) Viticulture Specialist, Dr. Jim Wolpert, tested 20 of these red winegrape varieties originating in warm climates at the UC-Kearney Agricultural Research and Extension Center in Parlier, CA. Factoring in yield and fruit quality parameters, some of the best performing varieties in this initial study were ‘Petite Sirah,’ ‘Petit Verdot,’ and ‘Tannat.’