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Grapes Don't Like Chilly Wet Mornings And Neither Do I

When I moved into my tent at the winery over a year ago I wondered why in the early morning I would hear what sounded like a fleet of helicopters landing in the vineyard. I now know that what I was hearing was the sound of vineyard owners battling the frost that threatened to destroy their grapes. If the temperature drops to below 32º F for more than 30 minutes there is a chance that ice crystals will form within the plants cells and destroy any green growth. During the spring when the buds are forming that will produce the fruit for harvest, the entire crop is vulnerable. In the fall early rains mixed with low temperatures can cause the grapes to shatter on the vine. Growers have developed a number of ways to combat this potentially disastrous scenario. Overhead sprinklers are one such technique. By covering the vines in water constantly the plant tissue will remain at 32º as long as the temperature is above 20º. The technique is effective but the systems are expensive, require maintenance and use about 55 gallons per acre per minute to be completely effective. That’s a lot of water. Heaters have also been used, though usually in conjunction with another method. Vineyard heaters for commercial use must comply with California emission standards but still can burn up to about a gallon of diesel fuel an hour per unit. Imagining the vast vineyards of California blanketed by these heaters makes the environmentalist in me cringe. The fans I mentioned earlier circulate the warmer air that is higher in the atmosphere. These can raise the temperature at the level of the grapes to 1/4th the difference between the temperature at 4 feet off the ground and 40 feet. So if there is a 4º temperature difference the fans will effectively raise the temperature at the height of the vines by 1º. The Department Of Agriculture’s Natural Resource Conservation Service is working with vineyards owners to switch to this method to conserve water. Maintaining soil that radiates heat effectively is an important component that can be utilized to bolster any frost protection strategy. Soil that is clean, firm and moist is best. Research recently done at the University of California, Berkeley indicates that the ice crystals that form in plant tissue must have a nucleus on which to form. Bacteria is what provides such a nucleus so by reducing the amount of ambient bacteria present on the vines the risk of frost should theoretically be reduced, though this strategy has yet to be implemented commercially. Frost damage is not a threat everywhere in California but in the Valley of the Moon where Deerfield Ranch Winery is located it is a threat that we contend with every year. We made it through spring without too much issue, though we did use our dual purpose irrigation system which makes use of water that is recycled by our on-site water treatment bioreactor. Usually, in Sonoma county, fall frosts which damage crops are rare because typically the fruit has been harvested. We can't seem to catch a break this year: A frost warning was issued for Wednesday morning. It looks like this time that the threat didn't materialize though. Deerfield is planning to pick its entire Syrah vineyard by mid next week. I'll let you know how it goes!



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Reader Comments (2)

Fantastic post, Im gratful to you!
Perfect writing, I learned so much! Working with nature is fun and exciting!
Would it be possible to make Ice wine in a special extra cold part of the ranch?

Hope you are staying cozy and warm in the Valley of the Moon

November 13, 2010 | Unregistered CommenterRuby

No ice wine Ruby, but we do make a late harvest Sauvy Blanc dessert wine that is very similar. Divine ambrosia... :)

November 22, 2010 | Registered CommenterThe Cellar Rat

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