###### Abstract  
Although coffee silverskin (CS) has recently been used as a food ingredient, no knowledge has been reported on the effects of species or different post-harvest treatments on its chemical composition. Therefore, the fibre, volatile compounds, phenolic acid content, and antioxidant capacity of CS samples obtained at three roasting intensities (light, medium, and dark) from the _Coffea arabica_ and _C. canophora_ species, each subjected to a washing or a sun-drying (\"natural\") post-harvest treatment, were studied. Obtained results showed that the chemical composition of CS is due to species, roasting, post-harvest treatment, and interaction. In particular, natural _Arabica_ CS showed the highest content of volatile compounds of Maillard and varietal origin, whereas washed _Arabica_ CS showed the highest content of soluble dietary fibre and chlorogenic derivatives. Pyrroles, sulphur compounds, and pyridines contents were higher in _Canophora_ CS than in _Arabica_ CS. The dark-roasted washed _Arabica_ CS showed the highest content of 5-O- and 3-O-caffeoylquinic acids, while the natural _Arabica_ CS highlighted the highest antioxidant capacity. The effect of post-harvest treatments seemed to be emphasised in _Arabica_ CS, independent of roasting, which did not significantly affect the antioxidant capacity of CS from either species.  
coffee silverskin; washed coffee; natural coffee; volatile compounds; polyphenols; antioxidants; roasting 2022113132[[https://doi.org/10.3390/foods111933213](https://doi.org/10.3390/foods111933213)]([https://doi.org/10.3390/foods111933213](https://doi.org/10.3390/foods111933213))  
of the coffee beans, is detached with a world production of about 0.4 million tons. CS is the main by-product of the coffee industry and in recent years, different characterisation studies on the bulk CS of undefined species have been conducted. The composition of this by-product shows a high dietary fibre content (56%), protein (18.8%), and minerals (almost 8.5% of ash). Potassium, magnesium, and calcium are the most abundant macrominerals, followed by Fe and Na. The total fat content is approximately 2.4%, whereas carbohydrates account for 5.8% of the chemical composition [5; 6; 7]. In addition, mandatory safety assays conducted on CS show the absence of pesticides and mycotoxins, and mitigation of other contaminants such as acrylamide [8]. CS is also characterised by the presence of caffeine, tannins, and melanoidins formed through the Maillard reaction during roasting [9; 10; 11; 12], as well as phenolic compounds and alkaloids with a high antioxidant capacity [13].  
Although CS has been mostly used as a combustible or fertiliser [14], the authors have suggested the use of CS as an important food ingredient that can be incorporated in several food formulations [15; 16; 17]. CS can be used as a raw food ingredient [18; 19; 20; 21; 22], but also as an extract to improve the quality of food [23; 24; 25; 26] and beverages [27].  
Despite these applications, to our knowledge, no further studies have been performed on the synergistic effects of coffee species (_Anabica_ or _Canephora_), post-harvest treatment (wash/wet or natural/dry), and roasting intensity on the chemical composition of CS. These aspects have been largely examined for raw and roasted coffee beans, showing significant effects on all chemical parameters [28; 29], aroma compounds [30; 31; 32; 33], and polyphenol contents [34; 35].  
The present study aimed to explore the effects of natural and washing processes and three roasting conditions on fibre, volatile compounds, and phenolic acid contents, as well as antioxidant activity of CS from _C. arabica_ and _C. canephora_.