## 1 Introduction  
Chitosan is a biopolymer made of 2-Amino-2-deoxy-poly-p-glucosamine and \(N\)-acetylglucosamine which is obtained from the deacetylation of chitin extracted from sources such as fungi, crustaceans, insects [1]. In the last decades, chitosan has aroused great interest in food industry due to its biocompatibility, biodegradability and low toxicity, being recognized as GRAS (generally recognized as safe) by the Food and Drug Administration (FDA) [2]. In 2011, the use of chitosan from _Aspergillus niger_ has been approved in oncology as an adjuvant for various purposes: clarification, reduction of heavy metal and toxins contents and for microbial stabilization [3]. Its insolubility in wine makes the removal by settling or filtration extremely easy. It has been demonstrated that chitosan treatments may lead to greater wine safety since it reduces the content of contaminating metals and ochratoxins [4]. Furthermore, chitosan is able to inhibit the growth of a wide range of spoilage microorganisms such as acetic acid bacteria, lactic acid bacteria and _Brettanomyces_ spp. yeasts [5; 6; 7]. These latter are spoilage yeasts responsible for the production of volatile phenols (4-ethyl phenol and 4-ethyl guaiacool) and the consequent development of the \"horse sweat\", \"smoky\" and \"leather\" character in wood aged or stored red wines, which are therefore severely compromised in quality. Already published results confirm that in red wines, the presence of 4-8 g/hL chitosan for 6-10 days can effectively prevent the microbial developments, thus avoiding the risk of the mentioned sensory defect [5; 8].  
In this regard, it is also worth reporting that some authors have observed a reduction in the content of volatile phenols in the headspace of spoiled red wines treated with chitosan [9; 10] which would suggest the potential for chitosan to remediate to adventitious development of _Brettanomyces_ spp. in stored products. For these reasons, chitosan represents an interesting tool to manage the aging stage of red wines in wooden barrels, especially in the case of sulfite-free winemaking [11; 12], where it may partially obviate the problems given by the absence of sulfur dioxide (SO\({}_{2}\)) [13].  
However, little is known about the overall impact of chitosan treatment with respect to the fixed and volatile composition of red wines, taking into account the mode and the timing of addition typical for this adjuvant. A recent bibliographic review [13] tried to collate the scientific data available on this argument. It was claimed that at dose \(<\) 1 g/L chitosan seems not to significantly impact the color, the aroma, and the phenolic composition of red wines, but further investigation would be needed.  
The aim of this work is, therefore, to evaluate the effect of chitosan applications on the chemical parameters of red wines, such as pH and titratable acidity and phenolic compounds especially phenolic acids, flavonoids and anthocyanins and to deepen into the possible change in their chromatic features by evaluating co-pigmentation and polymers contribution the color. Additionally, the effect of the treatment on the volatile and sensory profile of wines previously contaminated with volatile phenols will be investigated. The application of two distinct addition modes (e.g., powder or dissolved chitosan) has also been compared with the purpose to evaluate the influence on the cited parameters of the increase in the specific surface of the polymer, since this parameter has been previously suggested to potentially impact the efficacy of the polymer in particular with respect to _Brettanomyces_ spp. [7].