Partial dealcoholization of a Malbec wine through pervaporation with a PDMS membrane: Effect of operation temperature on process economics, volatile aroma composition and sensory properties

Abstract

In the present work, partial dealcoholization of a Malbec red wine with 14.8% v/v alcohol by pervaporation through a PDMS membrane (polydimethylsiloxane) was addressed. The influence of the process temperature on the economy of the process, the composition of volatile aroma compounds and wine sensory characteristics was deeply analyzed.To do so, partial dealcoholization experiments at lab scale were run with the pervaporation setup operated at a permeate pressure of 0.013 bar and at three different temperatures; i.e. 35, 40 and 45°C. Two types of runs were carried out: i) simple runs to build a conceptual model of the process and ii) repetitions to accumulate an adequate volume of partially dealcoholized wine (10.5% v/v) to allow the sensory analysis of the following Malbec wines: the initial wine, the partially dealcoholized wines and the blends in a 70/30 ratio (13.5% v/v)).From the conceptual modeling stage the required value of the fractional pervaporation advance η_req of 0.09 was obtained, as well as the average values of permeate overall fluxes at 35, 40 and 45 C; i.e., 1.02, 1.38 and 1.82 kgm-2h-1, respectively. For all variants, a permeate product with an alcohol content of 54% v/v was estimated. Experimental values agreed reasonably well with those obtained from the model simulation.The conceptual modeling of the process enabled the scaling-up of the process and the subsequent economic analysis. The best figures corresponded to the design with heat integration at 45°C when earnings estimated from the sale of the ethanol-rich permeate to the local market was taken into account.Fresh Malbec, partially dealcoholized wines at the selected temperatures, and their corresponding blends were chemical and sensory characterized. Dealcoholized wines showed differences concerning the operating temperature on the volatile and total acidity, fructose, anthocyanins, tannins, total polymers, and CIELAB parameters, except lightness. The total and volatile acidity were affected by the temperature and showed an increase in dealcoholized and blended wines with the respective decrease of the pH. Dealcoholization favored the presence of large polymeric pigments (0.6 in initial wines and an average of 0.96 in blends), which are associated positively with color stability. Volatiles were also affected by the operating temperature, decreasing the concentration of all chemical groups in these wines. A total of thirty-two free volatile organic compounds (VOCs) including higher alcohols (HA), medium chain fatty acid ethyl esters (MCFAEE), higher alcohol acetates (HAA), medium chain fatty acids (MCFA), norisoprenoids (NI) and terpenoids (TP) were identified and quantified.Finally, sensory evaluation demonstrated that partially dealcoholized wines could not be differentiated by the operation temperature. The fullness, astringency, pungency, floral notes, bitterness, color intensity, and sweetness were significant variables that allowed differentiate between initial, partially dealcoholized, and blend wines. Despite the loss of volatile compounds, blended wines showed higher intensity of floral attributes, and in mouth were lesser astringent, bitter, and pungent than the fresh wine. From an overall perspective, pervaporation of fresh wine with a PDMS membrane at 45°C and the adoption of a dilution ratio of 70/30 for initial wine to partially dealcoholized wine result in a promising strategy to reduce the alcohol content without affecting the sensory quality of the final red wine.