###### Abstract
In order to improve the extraction of the components of interest during the alcoholic fermentation--and particularly, the aroma-related compounds--a common practice is to extend the contact time between the must and the berry skins by means of a controlled maceration that favors the extraction of the compounds in the grapes' solid parts [16; 17]. Prefermentative maceration is maceration prior to alcoholic fermentation at low temperature (5 to 10 \({}^{\circ}\)C), which facilitates the extraction without loss of the aromatic fraction [18]. A study on the red variety Pinot nor from Burgundy revealed that the effect of cold pre-fermentation resulted in wines with a richer polyphenic content [19]. The effects of two prefermentative treatments (cold maceration at 6-8 \({}^{\circ}\)C and cold maceration at 0-2 \({}^{\circ}\)C using dry ice) were studied on the Monastrell grape variety, and an increase in the phenolic and aromatic fractions was reported in both cases. For phenolics, including anthocyanins, increases in the range of 10-20% were found, while increased levels for acetates and esters reached up to 23%, in some cases. However, both the starting level of sugars and the final content of the ethanol affect the extraction efficiency of compounds from the grape skins. In the case of anthocyanins, the effects were less intense in the musts with higher levels of sugars and higher levels of ethanol [20]. In warm climates, cold maceration for 10 days at 4 \({}^{\circ}\)C was tested on three red grape varieties: Tempranillo, Merlot and Syrah. The final wines showed an increment in total phenolic content (6-8%), anthocyanins (15-24%), tannins (6-8%) and aromatic compound content (up to 63%) in comparison with the control wines, thus improving the quality of the wines [21]. Maceration after freezing the berries at different speeds was also evaluated for the Muscat variety, and although the final wines were considered to be more aromatic, no significant (\(p\) = 0.05) color differences were observed [22]. The effects of prefermentative maceration and fermentation at low temperature were studied for Cabernet Sauvignon. The wines that were produced at low temperature proved to be more aromatic, although with a lower color intensity, while those that had been fermented at room temperature showed a greater color intensity and less aroma. However, different maceration times did not show any effects [23]. It could, therefore, be concluded that prefermetative maceration, in most cases, resulted in a significant increment in the extraction of compounds from the skins. This is particularly interesting with regard to volatile compounds, even if the extraction of phenolic compounds was also enhanced. In the case of the viniification of red wines, the effects of this winemaking technique are masked by the extractions that take place during the fermentation of the must while in contact with the solid parts of the grapes. Another approach used to enhance the diffusion of the compounds from the skins into the must is the application of an external source of power during the maceration or fermentation to facilitate the transferring of the compounds. One of the techniques that has gained popularity recently is the application of ultrasound in combination with maceration [24]. This technique is based on a phenomenon called \"cavitation\" where small bubbles collide with the surfaces of the solids that are in contact with the liquid that carries the ultrasound waves, thereby facilitating the transference of the solid compounds into the liquid [25; 26; 27]. This technique has been employed to extract a wide variety of organic compounds from different matrices, including the compounds with antioxidant activity that are found in grapevine leaves [28], the phenolic compounds from grape pomace, skin and seeds [29] or the phenolic compounds present in grapes as part of the method to determine ripeness indices [30; 31]. These abilities revealed by ultrasound are quite attractive for application to winemaking.