Ultrasound and microwave techniques to accelerate the release of oak wood compounds in wine aging process

Abstract

Aging process is an essential stage in the improvement of wine quality. This process is usually performed by contact with oak wood whose compounds are released and transferred to wine, acquiring typical aging bouquet. Although the use of oak chips is a practice generally accepted as alternative to barrels to shorten aging process, the application of emerging technologies is being unfolded to accelerate this stage. In this sense, non-thermal technologies such as ultrasound or microwave waves have been evaluated to compare their effect on the release of compounds from oak wood and their influence on the aromatic profile versus the use of oak wood chips.The concentration of the main compounds released to wine during aging process by means of oak chips (7 g/L) from two species (Quercus alba and Q. robur) was monitored every 6 time points for 24 days. Results showed that concentrations of trans- and cis-whisky lactones, furfural, vanillin, syringol, eugenol and guaiacol among others increased remarkably up to 8 days of aging, after which the increase was statistically insignificant. Taking these quantities as a reference, the same wine was subjected to contact with oak chips under different ultrasounds and microwaves treatments conditions to emulate aging process in the shortest possible time. On the one hand, ultrasound technique was applied to wine in contact with oak chips with a power of 400 W during 15 min, 2 h and 12 horas, the latter applied by hourly pulses. On the other hand, microwave technique was also handled by different treatments: 900 W during 10 min, and 700 W for 10 and 20 min.Results showed that wines subjected to treatments of ultrasounds 400 W during 12 hours by pulses and microwaves with 700 W for 20 min reached similar concentrations of compounds released from oak chips as wines macerated for 8 days. However, from a sensory point of view, the ultrasound treated wines showed similar scores in aging descriptors (vanilla, spice, wood, toast…) as wines macerated with oak chips for 8 days.Therefore, both techniques can be considered to bring an accelerated aging, significantly shortening the time required for it, which will undoubtedly be an advantage for wine industries. However, considering the sensory repercussions, ultrasound technique seems to be more feasible than the use of microwaves.