A chamber-free method of heating and cooling grape clusters in the vineyard

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 developme nt in wine grapes (cv. Merlot). Selected sunlit clusters were cooled to the temperature of shaded clusters; likewise, several shaded clusters were hea ted to the temperature of sunlit clusters. Cooling was achieved by forced c onvection via a 1525-W, commercially available air conditioner. Hot air was generated using 1.4-Ohm (100-W) resistance elements. Heated or cooled air was blown across fruit clusters at about 1.9 m.s(1) producing up to a 10 de grees C change in cluster temperature. Cluster temperatures were interrogat ed 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 syst em kept clusters within 2 degrees C of their desired target temperatures 99 % of the time. Heaters achieved the same performance 97% of the time. The m aximum observed increase of berry temperature above ambient air temperature (2 m above canopy) was 15.9 degrees C for the sun-exposed side of a west-f acing 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 fi eld for physiological studies of ripening and ripening disorders without ch anging other aspects of the cluster microclimate, an unavoidable consequenc e of chambers or enclosures.