PEF treatment of must and wine for on-line clarifying and fining

PEF application in winemaking mainly concerns the extraction of phenolic compounds from grape skins for red wines production. PEF-mediated fermentation control has also been tested with interesting results, and a considerable part of information has been collected on enzymes. There is a lack of data concerning the efficiency of PEF on the stability of chitinases and thaumatin-like proteins and, thus, on the application of PEF for wine fining purposes. This work aimed to test whether the application of PEF could trigger the cascade of phenomena that lead to the formation of haze in wines and if the altered condition allows an in-line filtration system to remove the aggregates and to stabilize the product. Parallel investigations of the stability of the color studied any possible deleterious consequence on the quality. The samples used for the study were 2016 Vitis vinifera L. cv Moscato bianco must and Vitis vinifera L. cv Sauvignon blanc wine. PEF treatments with monopolar square wave pulses were performed in a lab-scale continuous system. The must and wine samples were pumped at 25 L/min into a PEF treatment chamber with 1 cm distance between the stainless-steel electrodes. Acquisition of voltage and current was via a digital oscilloscope. Two different experimental plans were devised, one for the Muscat must and one for the Sauvignon blanc wine. On Muscat must the PEF treatment consisted of two different trials with a total input energy of W=100 kJ/ and W=150 kJ/kg, respectively. With regard to Sauvignon blanc wine, an additional trial with a cooling step subsequent to the heating induced by the PEF treatment was applied. At the inlet and outlet of the PEF system thermocouples recorded temperature every second. Sixteen hours after the treatment, the samples were filtered on 0.45 μm membranes and stored at 20°C for turbidity and color determinations up to 12 months. The results outlined that a combination of PEF treatments and membrane filtration reduced the Sauvignon blanc wine heat instability. Conversely, the Muscat must a significant increase of ΔNTU suggesting the inefficiency of the PEF treatments, possibly induced by the interaction with polysaccharides. As to the effects on color, Muscat must did not show any significant variation, while Sauvignon blanc wine showed a significant degree of pinking that disappeared 12 months after the PEF treatments.