Effects of a new vacuum evaporation method on chemical and sensory properties of must and wine

Abstract

A new process for vacuum evaporation was developed where evaporation takes place near the inner surface of a vortex produced by a rotor submerged in the liquid. Contrary to the state of the art the Vortex rotor process does not need a vacuum vessel but the rotating liquid creates a geometrically stable low pressure void surrounded by a vortex stabilized by the equilibrium between centrifugal forces and the pressure difference. First tests with water and sugar solutions at concentrations similar to grape must were conducted to verify the theoretical predictions, test the performance under different conditions and study the effect of various process parameters (Rösti et al 2015). The present paper shows the effects of the new vacuum evaporation method on chemical and sensory properties of must and wine in prototype trials at pilot scale using white and red winemaking protocols during three harvests. For white wine, must of Chasselas grapes was concentrated up to 15% after clarification with the new vacuum evaporation method and the effects on the wine quality was compared to concentration by inverse osmosis and sugar addition. For red wine, juice was drained from destemmed and crushed red Humagne rouge grapes at a third to half of the initial weight. This non-clarified juice was concentrated up to 30% with the new vacuum evaporation method before adding it back to the initial grapes for fermentation and maceration. During the concentrations of must, sugar and nitrogen compounds were increased proportionally. Acid compounds showed a more variable behaviour. Malic acid was generally increased similar to sugar compounds whereas tartaric acid decreased or increased before decreasing at higher concentration levels. The variable behaviour of tartaric acid can be linked to the equilibrium with potassium ions. The wines produced with the new evaporation method showed generally higher acidity than the control wines with sugar addition consistent with the results from the must analysis. White wines also showed an increase in phenolic compounds. In the sensory evaluation the white wines produced with the new evaporation method were generally preferred compared to the control wines with sugar addition. They were recognised for significantly more fruity aromas. The wines produced with inverse osmosis were rated intermediate. For red wines the sensory evaluation showed no clear trend so far with results ranging from insignificant differences to preference for the wine produced with the new evaporation method due to smoother tannins. Generally the results from these pilot trials are consistent with those from traditional evaporation methods. This shows the feasibility of applying the new vacuum evaporation method to white and red wine production. Its robustness towards high sugar levels and non-clarified grape juice together with the simplicity of the construction and the process handling make this new method a promising development for the wine production.