PEF treatments of high specific energy permit the reduction of maceration time during vinification of Caladoc and Grenache grapes

Highlights

• PEF of high specific energy permits reducing red winemaking maceration to 24 h.

• A fast increment of wine color intensity was promoted after few hours of maceration.

• PEF could result an alternative to maceration techniques based on grape heating.

Abstract

Phenolic compounds extracted from the solid parts of the grapes during the maceration-fermentation stage define many of the sensory attributes of red wine such as color, bitterness or astringency.

The effect of moderate a PEF treatment (M-PEF) (5 kV·cm⁻¹, 8.8 kJ·kg⁻¹) and an intense PEF treatment (I-PEF) (5 kV·cm⁻¹, 52.9 kJ·kg⁻¹) on the reduction of maceration time during vinification of Caladoc and Grenache grapes was investigated.

In both grape varieties, M-PEF treatment combined with 4 days of maceration was the most effective treatment in achieving high anthocyanin content, color intensity and total phenol index at the end of fermentation. The I-PEF treatment promoted a rapid release of anthocyanins and phenolic compounds, along with a fast increment in the color intensity of the must after 24 h of maceration. Although the color intensity and anthocyanin content decreased significantly throughout fermentation when grape pomace was removed after 24 h, these parameters were similar, after 3 months of bottling, in the case of Caladoc and slightly lower in Grenache than the control wine, for which maceration was extended for 10 days.

Therefore, results obtained in this investigation are the first to demonstrate the potential of I-PEF for the reduction of maceration time to 24 h in red winemaking.

Introduction

Over the last decades, considerable research efforts have been devoted to the development of non-thermal processing technologies (Zhang, Barbosa-Cánovas, & Balasubramaniam, 2011). These technologies permit improving different unit operations in the food industry such as extraction providing more sustainable and eco-friendly processes (Chemat et al., 2017).

PEF technology is regarded as a promising alternative to thermal processing with the purpose of improving microbial inactivation (Wang et al., 2018), mass transfer (Puértolas, Luengo, Álvarez, & Raso, 2012), and structure modification (Oey, Faridnia, Leong, Burritt, & Liu, 2017). The treatment generates a high intensity electric field between two electrodes by applying pulses of high voltage and short duration. The effects of PEF on foods are attributed to a presumed structural rearrangement of the cell membranes called electroporation, which consists in the formation of local defects or pores (Kotnik, Rems, Tarek, & Miklavčič, 2019). The electroporation of grape skin cells with the purpose of improving the extraction of phenolic compounds during the maceration-fermentation step in red winemaking is one of the most widely investigated applications of PEF in recent years (Ricci, Parpinello, & Versari, 2018). Maceration is one of the most critical stages in red winemaking. During maceration, phenolic compounds that define many of the sensory attributes of red wine such as color, bitterness or astringency are transferred from the skins and seeds into the must (Bautista-Ortín, Busse-Valverde, López-Roca, Gil-Muñoz, & Gómez-Plaza, 2014; Busse-Valverde et al., 2010). Obtaining a wine with enough polyphenol content required that the solid parts of the grapes remain in contact with the fermenting must between 7 and 10 days. In order to increase its production capacity, wineries are interested in shortening the maceration time without affecting wine quality.

Different studies conducted in the laboratory, but also at pilot plant and semi-industrial scale, have demonstrated that PEF treatments can allow winemakers to reduce maceration time and/or obtain a wine with a greater amount of phenolic compounds (Puértolas, López, Condón, Álvarez, & Raso, 2010). In view of such effects, PEF could become an alternative to techniques such as thermovinification or flash release, currently used in wineries to improve polyphenol extraction based on the heating of grapes. Whereas thermovinification consists in heating grapes at temperatures between 70 and 75 °C for a period ranging from 30 min to 24 h (Sacchi, Bisson, & Adams, 2005), the process known as “flash release” consists in a rapid heating of grapes (85–95 °C) with direct steam injection, after which grapes are exposed to a vacuum that induces instant vaporization of the water they contain, thereby cooling them and weakening their skin cell envelopes (Moutounet & Escudier, 2000). After application of these techniques, solid parts of the grapes are removed after few hours of maceration and fermentation is conducted in liquid phase. The benefits of fermenting in liquid phase include a better use of the effective volume of the tanks, an improved control of fermentation temperature, and savings in labor as well as in the energy consumption required to periodically pump the wine over the skin mass that rises to the top of the fermentation tanks.

Although it has been demonstrated that electroporation of grape skins by PEF significantly improves the extraction of polyphenols such as anthocyanins and tannins, a certain maceration time is required to obtain wines with a sufficient amount of these compounds (López, Puértolas, Hernández-Orte, Álvarez, & Raso, 2009). Typical maceration times reported by different authors for wines obtained with grapes treated by PEF range from 3 to 6 days (Maza et al., 2019).

In the present study, intense PEF treatments in terms of specific energy were applied to electroporate grape skins of two grape varieties (Caladoc and Grenache) in order to evaluate whether the maceration step could thereby be reduced to just a few hours.