**6. Ultrasound**

*Chemistry and Biochemistry of Winemaking, Wine Stabilization and Aging*

conveyor (**Figure 12**).

of pigments in juice (**Figure 13B**) [16].

*Electron beam accelerator and detail of the irradiation process.*

treat each irradiated section several times in a second. The electron beam is moved by using intense electromagnetic fields. When the food is moved below the treatment plane, all food volume is irradiated. The received dose depends on the speed at which the food moves below the irradiation section that is controlled by using a belt

The external appearance of foods after irradiation frequently remains unaffected; sometimes, a brighter outer aspect can be observed (**Figure 13A**) [16]. Irradiation doses of 0.5–1 kGy produce 1 log reductions in yeast and lactic acid bacteria in grapes [16] without modifications in the external appearance and firmness [16]; similar effects have been observed in other fruits [49, 50]. Irradiation dose of 10 kGy produces 6-log reductions in yeasts and 3-log in bacteria [16]; this dose decreases firmness and softens the texture of grapes, thus enhancing the extraction

Irradiation can also be considered non-thermal technology with high efficiency to eliminate indigenous microorganisms from grapes. This reduction in the population of microorganisms allows a better implantation of selected yeasts and the reduction in SO2 doses. Depending on the irradiation dose (10 kGy), better

*(A) External appearance of grapes irradiated at 0.5, 1, and 10 kGy. (B) Color of juice from the irradiated* 

**38**

**Figure 13.**

**Figure 12.**

*grapes.*

Ultrasound (US) is sonic waves with a frequency range of 20–100 kHz producing cavitation phenomena with locally extreme temperature and pressure. Cavitation is generated by compression-decompression cycles producing the formation and implosion of gas bubbles [51] (**Figure 14**). This phenomenon produces intense agitation and dispersive effects that help to disrupt vegetal tissues, depolymerizing cell walls and favoring a better extraction. US efficiency in extraction processes improves when the frequency is closed to 30 kHz [52].

US technology can be used in winemaking for continuous processing of crushed grapes. As a consequence, there is a weakening of the cell wall and an increase in the extraction of tannins, pigments, and aromatic compounds [15, 19, 20, 52]. This effect can also be enhanced with the use of pectolytic enzymes [53]. When enzymes are used as the sole extraction technique, tannin concentration is 13% higher while, after US treatment, there is an increase of 16%. The initial use of enzymes followed by the subsequent application of US is especially synergistic increasing color intensity (18%) and tannin content (30%) [53].

Antimicrobial effect of US is quite reduced, and the intensity and time needed normally produce significant increments of temperature. Therefore, it is difficult to consider US as a non-thermal technology. However, US produces synergistic antimicrobial effects when applied together with conventional thermal technologies or emerging non-thermal processes.

Industrial devices are currently available to process crushed grapes increasing extraction and reducing maceration times. The sonication device has a tubular structure to increase sonication surface, normally with a polygonal section to better dispose of the sonoplates (**Figure 15**). Currently, this technology is developed by several companies; among them, Agrovin inside a H2020 European project, has developed the Perseo™ system [54] with 50 kW of power and 8 cavitation cells to process up to 10 t/h [52, 54]. With this technology, it is possible to reduce maceration times from 7 to 2–3 days with similar contents of anthocyanins and tannins; moreover, the aromatic fraction is in the same time enhanced. Prof. Emilio Celotti

#### **Figure 14.**

*Implosion of bubbles and cavitation produced by alternative compression-rarefaction effects generated by US waves.*

**Figure 15.** *Cavitation cells disposed in a tubular structure with the sonoplates to apply the US waves.*

(Udine University, Italy) is also working in the use of US to improve the maceration process and has developed a prototype to favor a faster extraction of polyphenols, aroma, and precursors [55, 56].
