Submitted to: American Journal of Enology and Viticulture
Publication Type: Peer reviewed journal
Publication Acceptance Date: 5/10/2000
Publication Date: N/A
Citation: Interpretive Summary: Laboratories and greenhouses cannot duplicate the natural environment of an agricultural crop. Therefore, experiments in plant science often must be conducted in the field, vineyard, or orchard where the crop is normally grown. To study the disorder of sunburning in wine grapes, a unique research system was developed for maintaining close temperature ranges on grape clusters in the vineyard without unduly altering other environmental conditions around the fruit. The system should be easily adaptable by other researchers who are interested in the tight temperature controls that are necessary in physiological studies of fruit crops. Cold air was generated with a 1525-W, commercially-available air conditioner and hot air with 100-W resistance elements. Heated or cooled air was blown across fruit clusters at about 375 feet per minute, producing up to 18 degrees F increase or decrease in fruit temperature. A control system adjusted heaters and coolers every 5 seconds. The cooling system kept clusters within 3.5 degrees F of their desired target temperatures 99% of the time, while heaters achieved the same performance 97% of the time. The system ran continuously for 60 days during fruit ripening.
Technical Abstract: 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 fully shaded clusters; likewise, several shaded clusters were heated to the temperature of fully sunlit clusters. Cooling was achieved by forced convection via a 1525-W, commercially-available air conditioner. Hot air was generated using 100-W resistance elements. Heated or cooled air was blown across fruit clusters at about 1.9 m/s, producing up to a 10 degree Celcius change in cluster temperature. Cluster temperatures were interrogated every 5 sec. The temperatures of fully sunlit and fully shaded clusters were used as set-points for the heated and chilled clusters, respectively. The cooling system kept clusters within 2 degrees Celcius of their desired target temperatures 99% of the time. Heaters achieved the same performance 97% o the time. The maximum observed increase of berry temperature above ambient air temperature was 15.9 degrees Celcius 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.