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Drying optimization, to mitigate fungal growth and <i>Ochratoxin A</i> (OTA) contamination is a key topic for raisin and currant production. Specific indicators of environmental conditions and drying properties were analyzed using two seedless grape varieties (<i>Crimson</i>—red and <i>Thompson</i>—white), artificially inoculated with <i>Aspergillus carbonarius</i> under open air and tunnel drying. The air temperature (T), relative humidity, grape surface temperature (T_s) and water activity throughout the drying experiment, the grapes’ moisture content and the fungal colonization and OTA contamination during the drying process and their interactions were recorded and critically analyzed. Drying properties such as the water diffusivity (D_eff) and peel resistance to water transfer were estimated. The grapes T_s was 5–7 °C higher in tunnel vs. open air–drying; the infected grapes had higher maximum T_s vs. the control (around 4–6 °C). OTA contamination was higher in tunnel vs. open air–dried grapes, but fungal colonies showed the opposite trend. The D_eff was higher in tunnel than in the open air–drying by 54%; the infected grapes had more than 70% higher D_eff than the control, differences explained by factors affecting the water transport. This study highlighted CFU and OTA indicators that affect the water availability between red and white grapes during open air and tunnel drying, estimated by the D_eff and peel resistance. This raises new issues for future research.