## 1 Introduction  
In the EU, around 129 Mt of food waste is generated annually in the food supply chain [1]. It not only has economic repercussions, but it also presents an environmental impact as a consequence of the management and disposal of the food waste [2, 3]. The current situation demands for a change from a linear economy to a circular economy where by-products acquire an added value and re-enter the production cycle in order to decrease the environmental impact of industries [4]. It is particularly concerning to the winemaking industry, which includes the production of Cava. Cava is sparkling wine with Protected Denomination of Origin (PDO) that requires a second fermentation in the bottle with a biological ageing process in contact with lees for a minimum of 9 months [5]. Wine elaboration produces approximately 25 kg of waste for every 100 kg of processed grapes. Actually, the main solid residues produced by winemaking are grape pomace (60%), lees (25%) and stalks (15%) [2, 3]. Lees are the residue formed during wine fermentation and consist, mainly, of naturally plasmolyzed cells of _Saccharomyces cerevisiae_, tartaric acid and other adsorbed compounds [6, 7]. It is estimated that the production of Cava lees is about 300 tones per year [8]. Those lees are rich in phenolic compounds as well as fiber and proteins from the cell wall of _S. cerevisiae_[2, 5, 6, 7]. Indeed, the use of by-products with high contents of fiber and other bioactive compounds as novel ingredients is being studied to obtain foods with greater nutritional value [9, 10, 11]. Despite their composition, lees are an undervalued by-product mostly used for the recovery of tartaric acid and distillation to obtain alcohol [12]. Nevertheless, some studies have reported the possibility of revalidizing wine lees [8; 13; 14; 15]. In fact, [PERSON] et al. (2021) [6] reported an improvement of growth and survival of lactic acid bacteria (LAB) with the addition of Cava lees in vitro. In addition, our research group recently demonstrated that the addition of Cava lees to sourdough formulation promoted the growth and survival of microorganisms (both LAB and yeast) in spontaneous fermentation [15]. In addition, it has been reported that Cava lees can inhibit the growth of pathogens (_Salmonella_ spp. and _L. monocytogenes_), improving the microbiological safety of fermented sausages [6]. Hence, Cava lees might be revalorized as a food ingredient to improve fermented foods like sourdough and bread. Moreover, modifying microbial populations of food fermentation might have an impact on its flavor [16]. Indeed, flavor and especially odor are of great importance for consumer acceptance. It must be taken into account that the addition of by- and co-products to food formulation may change its sensory properties (from texture to aroma or color). For instance, [PERSON] et al. (2018) [9] added broccoli co-products (stems and leaves) to wheat bread formulation to obtain functional products with enhanced concentrations of fiber and phenolic compounds. The researchers observed that breads with broccoli presented an increased green hue as well as a higher color intensity in crumb and crust. Nevertheless, when performing sensory tests, the overall acceptance of the breads was not affected by broccoli incorporation [9]. Other by-products, such as cumin and caraway seeds by-products and cocoa dietary fiber have been added to wheat bread formulation to obtain functional products [10; 11]. In both studies, researchers examined the effect of those new ingredients on the sensory properties of bread. In both cases, there were no significant differences on the overall acceptance of the fortified breads and controls, even though color, texture and aroma changed. In that regard, lees are able to adsorb volatile compounds during the biological ageing of sparkling wine [17]. Consequently, incorporating Cava lees to sourdough and bread formulations may add new odors and other compounds to such bakery products.