A Chamber-Free Method of Heating and Cooling Grape Clusters in the Vineyard

¹ USDA-ARS, 24106 N. Bunn Road, Prosser, WA 99350
² Department of Food Science and Human Nutrition, Washington State University—Irrigated Agriculture Research and Extension Center, 24106 N. Bunn Rd., Prosser, WA 99350.

jtarara{at}tricity.wsu.edu

A device was constructed to heat and cool grape clusters (Vitis vinifera L.) in the vineyard as part of a larger study on sunscald and color development in wine grapes (cv. Merlot). Selected sunlit clusters were cooled to the temperature of shaded clusters; likewise, several shaded clusters were heated to the temperature of sunlit clusters. Cooling was achieved by forced convection via a 1525-W, commercially available air conditioner. Hot air was generated using 1.4- (100-W) resistance elements. Heated or cooled air was blown across fruit clusters at about 1.9 m·s¹ producing up to a 10°C change in cluster temperature. Cluster temperatures were interrogated every five seconds to activate or deactivate heaters and/or cooling fans as needed. The temperatures of sunlit and shaded clusters were used as set-points for the heated and chilled clusters, respectively. The cooling system kept clusters within 2°C of their desired target temperatures 99% of the time. Heaters achieved the same performance 97% of the time. The maximum observed increase of berry temperature above ambient air temperature (2 m above canopy) was 15.9°C for the sun-exposed side of a west-facing cluster. The control system operated continuously for 60 days between bunch closure and harvest. This heating and cooling technique can provide in-situ replicated measurements of berry and cluster temperatures in the field for physiological studies of ripening and ripening disorders without changing other aspects of the cluster microclimate, an unavoidable consequence of chambers or enclosures.

Key words: microclimate, canopy management, light, solar radiation, fruit temperature, berry temperature

Submitted on January 13, 2000
Revised on March 13, 2000

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