Heat pump drying of grape pomace: Performance and product quality analysis

Abstract Grape is one of the most popular fruits and various types of grape have been cultivated by more than 100 countries around the World. The wine and juice industry produces large quantities of by-product, called grape pomace (GP) as an industrial waste and it consists of skins, seeds, and stems. Various processes such as separation, pressing, drying, and milling are applied to benefit from its health effects. In this study, the seeded black GP Kalecik karası (Vitis vinifera) was dried in an assisted closed cycle heat pump dryer (HPD) designed for high-moisture products to investigate the drying behaviors of GP. The effects of drying air temperature on bioactive properties and the drying characteristics of GP, and performance of system have discussed. Experiments were carried out at two different temperatures (45 and 50°C) and air velocity of 1.0 m/s. It was seen that increasing temperature decreased the drying time, coefficient of performance of whole system (COPws), and specific energy consumption (SEC). The average values of COPws for temperatures 45°C and 50°C were calculated as 3.28 and 3.10, respectively. The drying efficiencies (DE) at drying air temperature of 45°C and 50°C ranged from 2 to 12% and from 2 to 15%, respectively. Additionally, result of analysis has indicated that using a HPD at lower temperatures increases performance of system despite of higher energy input. Bioactive properties of dried samples at drying air temperature of 45°C are better than 50°C. The results show that drying the GP at low temperature is more suitable for product quality. For this reason, heat pump may be preferred. It shows that this drying system with higher capacities in the future can be recommended as an alternative technique in terms of energy usage, drying time, and performance of system.