TRUCKIN’ A grape-harvesting truck is positioned around midnight near a Dry Creek Valley vineyard.

This content is provided by Pierre Ratte.

That sound heard in the middle of the night? It might not have anything to do with Halloween ghosts or goblins, but rather with trucks and grape-harvesting machinery. It’s a bit spooky to have an 18-wheel tractor-trailer truck wander off the highway, down a bucolic country lane and then bump along a dirt farm road with its metal bins, in the middle of night.

Grapes are harvested at night to control temperature, improving fermentation and making better wine with less energy. Diurnal temperature differences along Dry Creek can vary 40 degrees Fahrenheit or more; this evening the temperature was 38 degrees. Nighttime grapes will have a uniform temperature and are not affected by sun and shade, with less sugar and more balanced acidity providing better flavor profiles.

Juice from cold grapes does not need to be cooled in water-jacketed fermentation tanks—the big stainless-steel tanks with large dimples are double-walled cooling tanks, affordable only to larger winery operations. Cooler grapes give winemakers more control over fermentation, giving us better wine. The cooler growing season, which has been delayed about 20 days, is causing late harvests and possibly spectacular wines.

Fun facts: Fermentation is a chemical breakdown of substances by bacteria, yeast or other microorganisms, which produces heat. One calorie of energy is required to lower one gram of water one degree Celsius. The double tractor-trailer here can haul 25 tons of grapes, with, say, 160 gallons of juice, called “must,” per ton. Power required to change daytime grape temperatures of juice from this truck to nighttime temperatures might amount to 1.4 million Kw.

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