Evaluation of selected parameters of mechanical and pneumatic press during grape pressing

Abstract

Modern wine technologies aim for selecting and optimizing the applied technological procedures, including the technical reinsurance of individual operations. One of the key operations, within the wine industry, with a direct impact on the quality of the produced wine is the process of grape pressing. The purpose of pressing is to separate the mold from the processed product by using pressure. The pressing efficiency, exerted by molding, is influenced by the particular type of the pressing device, the varietal properties affecting the consistency of the molded material, the pre-compaction process (crushing, maceration), the thickness of the mold and the number of the pressing cycles. This paper focuses on evaluation of the mechanical horizontal press WOTTLE RS 800 and the pneumatic press ŠKRLJ PST 80, with a volume of 800 litres pressing bins, that were evaluated during the period 2015-2017, while pressing the Sauvignon Blanc and Zweigeltrebe grape varieties. During the evaluation, the main focus was on monitoring the process of pressing, the change of the pressing pressure and its maximum achieved value, the average molding and the performance of the pressers. The results obtained show that, when pressing grapes by a mechanical press, the maximum pressure values are 0.51 MPa while the molding is in the range of 0.748-0.858 depending on the variety. For the pneumatic press, the maximum pressing pressure was 0.15 MPa and the mold variation was between 0.803-0.865. The mechanical press performance of the Sauvignon Blanc variety was 268 l•h-1 , 445 l•h-1 for the pneumatic press. For the Zweigeltrebe variety, the performance of the mechanical press varied at 715 l•h-1 and of the pneumatic press at 713 l•h-1. The results of the evaluation illustrate the differences arising from the used press and have practical use in wine-making practice and in designing the technological equipment of the wine-growing operations. At the same time, they can serve as inputs when calculating wine production costs.

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

“…This is an advantage that would be more important when processing more "difficult" grapes than the studied ones, with larger and slipperier peels and that are more likely to block the grid. In the latter cases, a pneumatic press would be less effective than a mechanical press, in terms of yield [7,14].…”

“…Pressing destemmed-crushed grape usually takes sensible technical and technological benefits, although it is possible to press whole grapes or employing retracted impeller pumps, as well as a more rapid filling phase. It grants best performances for the press, a faster must transport and reduces the risk of starting unwanted fermentations while the must is within the press [9].…”

“…Zemanek et al [14] compared functional performances of a pneumatic press and a mechanical one processing the same grape variety. Results showed that, with a mechanical press, maximum pressure value was 0.51 MPa for a must moulding between 0.748 and 0.858, depending on variety.…”

“…The results in the scientific literature concern the performance of oenological presses in terms of quantity and quality of extracted must. They were obtained only on specific grape varieties: Albana, Trebbiano, Listan Blanco, Sauvignon Blanc and Zweigeltrebe [6,11,12,14], which are not very common cultivars in the wine production of the Apulian Region (Italy). This article focuses on the purely energy performance of two types of pneumatic presses, in relation to the quantity of obtained must and their pressure working cycles, as they influence the performance of the machines in terms of sustainability and production economy.…”