## 1 Introduction  
One of the strategies to produce adequate base wines for red sparkling wines is based on early harvesting to obtain the optimum levels of alcohol content, acidity and pH for the second fermentation. These wines show little colour intensity and are unbalanced, with overly bitter, green and asrtingent notes, and with an inadequate structure in the mouth. To solve this, an ageing on lees of the base wine can be carried out.  
Among the different enological practices to produce sparkling wine, the traditional champenoise method, consisting of a second fermentation and the ageing on lees of a base wine in a bottle for a variable period, is characterized by the development of a more complex aromatic profile compared with other sparkling wines. Generally, the evolution of the aromatic components from the base wine to the final mature sparkling wine is associated with a long-lasting period of ageing, as it occurs with the best millesimes from French Champagne and Spanish Cava. Research has so far focused mainly on the ageing period of these wines; nevertheless, a recent study emphasizes the importance of the base wine in the characteristics of the final sparkling wine, independently of the time of contact with the lees [1].  
Ageing on lees is an enenological technique, widely used in both still and sparkling wines, that consists of keeping the wine in contact with its fermentation lees for a variable period of time in order to allow the autolytic process to take place [1,2]. Autolysis consistsof a self-degradation of dead yeasts by their own enzymes, releasing compounds from the cytoplasm and cell wall to the wine (mainly glycoproteins, polysaccharides, nucleic acids and lipids) [3]. In traditional sparkling wines, the ageing on lees period must be of at least 9-12 months [4], with a significant impact on the production costs. For this reason, several researchers have focused their activity on finding technological strategies to reduce this ageing time by accelerating the autolytic process [5].  
Ultrasound waves of high frequencies (above 20 kHz) have been used to disrupt cells [6], enhancing the release of macromolecules from yeast lees (glycoprotein and polysaccharides, mainly) [7; 8]. [PERSON] et al. [9] were the only researchers, to our knowledge, to evaluate the effect of sonicated lees in the ageing on lees process of a red wine, finding that several enenological parameters were positively affected. However, as mentioned above, the physico-chemical and sensory characteristics of a red base wine are different from a conventional red wine, mainly due to the early harvesting used in the production of the former. In this context, the hypothesis of this study was that the use of ultrasound-treated lees during the ageing of a red base wine would improve the wine quality. To confirm this, a specific study on the effect of sonicated lees on the ageing on lees of a red base wine has been carried out.  
In previous studies, we compared the ageing on lees of a model wine with lees treated by ultrasound and high hydrostatic pressure. After 42 days of ageing, our study found better results with sonicated lees than with pressurised lees, as well as significant differences between the wines aged on sonicated and unsonicated lees [10]. In this study, our research was carried out with a red base wine of Tempranillo variety added with sonicated lees during an ageing period of four months. Oenological parameters, volatile organic components and sensory properties of the wines were evaluated.