Abstract
This study evaluated the physical properties and oil extraction from grape seeds from three white (Welschriesling, Green Veltliner, Hibernal) and two red (Zweigelt and Saint Laurent) must varieties of grapevine by cold screw pressing as the appropriate extraction process. Pressing was carried out by a screw press UNO FM 3F by Farmet Company, Czech Republic. The pressing device consists of a matrix, 220 mm screw, head, heating mantle, nozzle holder, and a nozzle of 10 mm in diameter. The minimal and maximal screw rotation speeds were chosen within the press characteristics in order to achieve a correct expression and to avoid press overload. For successful pressing of the seeds and their storage, their initial moisture content was lowered from 40 to 45% to about 5 to 8% in a chamber dryer. The temperature in the chamber dryer did not exceeded 40 °C. Seeds of all varieties were pressed at the same speeds of 20, 40, 60, and 80 rpm. The characteristics of the grape seeds are as follows: The density ranges from 602.7 to 606.3 kg.m-3, thousand seeds weigh is between 21.9 - 26.6 g, humidity between 5.6 - 7.1% of dry matter and seed oil content, determined by extraction and depending on the variety, ranges from 15.3 to 17.5% in dry basis. The results have confirmed that when the screw rotation speed is changed from 20 to 80 rpm, the press capacity increases on average from 0.84 kg.h-1 to 1.75 kg.h-1, but simultaneously the oil yield reduces from 9.85 to 6.75%. This means that one kilogram of seed may produce 67.5 to 98.5 g of oil. The quantity of the pressed oil ranges from 67.5 to 98.5 g.kg-1 and thus depends on the variety. The measured results can be used in commercial practice for optimizing the pressing process for pressing of oil from grape seeds.
Highlights
A large volume of winery waste remains unexploited every year on an international level
This study evaluated the physical properties and oil extraction from grape seeds from three white (Welschriesling, Green Veltliner, Hibernal) and two red (Zweigelt and Saint Laurent) must varieties of grapevine by cold screw pressing as the appropriate extraction process
The measured results can be used in commercial practice for optimizing the pressing process for pressing of oil from grape seeds
Summary
A large volume of winery waste remains unexploited every year on an international level. Grape processing and subsequent production of wine is associated with the production of large quantities of waste. The most common among them are grape marc and wine lees. Winemaking wastes, traditionally considered an economic and environmental problem, are increasingly becoming recognised as valuable commodities for the production of value added products, such as grappa or vine seed oil (Passos, 2009). Mechanical extraction (pressed oil) and chemical or solvent extraction (Soxhlet methods and hexane as solvent) are the most common and widespread methods of extracting grape seed oil. To ensure higher oil quality, mechanical pressing is preferred. It uses lower process temperature and no solvent lower yields between 55 – 95% are achieved depending on the processed raw material (Singh and Bargale, 2000). Screw pressing has been studied for a large variety of oilseeds, including linseed, canola, crambe, and chia seeds (Savoire et al, 2013)
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