Italy is testing extreme enology
Cold soak and must freezing with dry ice are effective tools for the new enology, but the next frontier is represented by pulsating electric fields
It is well know that the pre-fermentative maceration at low temperature (cold soak) is useful to improve the aromatic composition of white wines and to increase the proanthocyanidin concentration of some varieties. In the same way, the use of dry ice to freeze the must for a better control of the alcoholic fermentation is now widespread. These techniques are now considered outdated, though: the new frontier of extreme enology is the employment of pulsating electric fields.
High-tension pulsating electrical discharges (PEF) in watery solutions of different foods (such as apple juice, semi-skimmed milk, eggs, pea soup) have strong effects on the microorganisms in the solution, with a significant increment of the shelf life.
The treatment employs very high voltages (20 to 80 kV) and induces the breaking – or lysis- of the cell membranes of bacteria. The treatments are extremely short, microseconds, and the temperature increase is very low, typically between 2 and 5 °C, depending on the equipment.
This treatment induces the inactivation of a vast variety of microorganisms, including Escherichia coli O157:H7, Salmonella spp. Staphylococcus aureus, Lactobacillus spp. Bacillus subtilis, Saccharomyces cerevisiae, Klebsiella pneumoniae, Pseudomonas aeruginosa, Pseudomonas fluorescens, Listeria monocytogenes and Zygosaccharomyces bailii. Spores are normally resistant to pulsating electric fields, so the efficiency is limited and for a complete eradication of such microorganisms other treatments should be employed in combination with PEF.
If this technique was in the past used just as an alternative to pasteurization, now enology can also exploit some of its side effects. PEF have been recently tested for the production of new red wines from Aglianico and Piedirosso grapes to increase the polyphenolic content. Before fermentation and maceration the grape skins were treated with PEF at different intensities (from 0.5 to 1.5 kV/cm, with an energy input of 1 to 50 kJ/kg), starting from a characterization of the product permeability by impedance measurements.
The kinetics of release of polyphenols and anthocyanins was recorded during maceration by spectroscopy and Folin-Ciocalteu colorimetric methods, respectively. Finally, the total acidity, the reducing sugars pH, the color intensity, the polyphenolic and anthocyanin total content, the oxidant activity and the composition of volatile compounds were monitored in the wine after pressing.
The PEF treatments on the Aglianico grapes induced a 20% increase in the polyphenols release, a +75% in anthocyanins, ameliorated the color intensity (+20%) and the antioxidant activity of the wine (+20%), by preserving all the organoleptic characteristics. On the contrary, the effects were marginal on the polyphenolic content of the Piedirosso grapes, besides the high degree of permeabilization of the cellular membrane.
Francesco Dons, Giovanna Ferrari, Marina Fruilo, Gianpiero Pataro - Pulsed Electric Field-Assisted Vinification of Aglianico and Piedirosso Grapes - J. Agric. Food Chem., 2010, 58 (22), pp 11606–11615