Experimental study on conversion of blanched grapes to raisins without chemicals through solar dryer to reduce drying time

• Reduction in solar drying time with use of blanching pre-treatment of grapes. • The method employed avoids use of any chemicals during drying of grapes. • Experimental observations related to the temperature profiles presented. • Efficiency and drying rate of dryer, and scope of future work discussed. Solar dryers are solar thermal devices which increase the drying temperature and aid in moisture removal from the load, leading to faster drying of the agri-product as compared to the open sun drying. Conversion of grapes to raisins can be effectively achieved through solar dryers, and efforts are ongoing to improve the efficiency and further reduce the drying time. Usually in order to reduce the drying time for the conversion of grapes to raisins several pre-treatment methods with the use of chemicals are employed. In the present work pre-treatment in the form of blanching of grapes is adopted without the use of any chemicals to study the effect on the drying time in the solar dryer. The experimental results have been compared with the study of conversion of grapes to raisins with the same solar dryer without blanching. It is found that pre-treatment in the form of blanching resulted in a reduction in drying time to almost half. Experimental observations for the temperature profile studies relating to ambient temperature, air temperature inside the dryer, base plate temperature and solar radiation are presented in the form of graphs and calculations have been carried out for the estimation of drying rate and efficiency.