Experimental Evaluation of Functional and Energy Performance of Pneumatic Oenological Presses for High Quality White Wines

In this article, experimental tests on two different kinds of pneumatic presses have been carried out in two Apulian wineries to evaluate energy consumption related to yield performance. The presses are employed to process Bombino Nero variety grapes, crushed and transformed in rose wine though a pomace less process. The pneumatic pressured press realized a 2 h:48 min long process, with a maximum pressure on the product of 1.4 bar and a must moulding of 69% of extracted must. In regard to the vacuum press, the process duration is 3 h:18 min, with a maximum pressure of 0.9 bar and a must moulding of 58%. During the pressing operation, mean values of must flow rate are comparable: 2.1 L min(-1) m(-2) for the pressured press and 2.9 L min(-1) m(-2) for the vacuum press. However, a more detailed analysis gives more insight on the behaviour of the two presses. In regard to the pressured press, a compression phase characterized by few steps and at lowest pressure values has proven particularly effective, especially in the first phase (must moulding of 41% with a must flow rate of 4.6 L min(-1) m(-2)), at the lowest pressure values. On the other hand, by analysing vacuum press process, the phases sequence is much more gradual, must moulding decreases as the extraction proceeds (from 28% to 6%), and in the last three phases a very low amount of must is extracted, with must moulding smaller than 10%. The energy consumption of the pressured press during compression is mainly related to the engine power absorption (one of the two in operation), and it is below 4 kW except during start-up, due to the starting currents. The highest power is reached in the last phase in which the maximum pressure is applied and a great amount of must is extracted. On the other hand, energy consumption in the vacuum press gradually decreases. A similar trend was not observed for the specific energy for either press: while it increases along the whole process for the vacuum press, it reaches a maximum value in the second phase of the pressured one. Results show the need to pursue new studies on single component design and on pressing cycles, especially in high-capacity pneumatic vacuum presses. Several advantages on wine production costs could be achieved, even retaining high quality wines.