## 3 Results  
The results of the BMP tests show that the liquid substrates analyzed show a significantly higher methane yield per kilogram of volatile solids than the solid ones. This fact is representative of the biodegradability of the substances in these substrates and of their availability for the methanogenic microorganisms. However and due to the low concentration of TS in the liquid by-products, the final yields of biogas per kilogram of total sample were higher in solid substrates except for exhausted grape marc. The specific methane productions of the different substrates obtained in the BMP tests are shown in Figure 1, expressed as L\({}_{\rm N}\) CH\({}_{4}\) kg\({}^{-1}\) VS and in Figure 2 as L\({}_{\rm N}\) CH\({}_{4}\) kg\({}^{-1}\) fresh sample.  
Figure 1: Total specific methane production of by-products from the alcoholic beverage production in L\({}_{\rm N}\)CH\({}_{4}\) kg\({}^{-1}\) vs. from the BMP tests (SD for each substrate: PA, 13; T, 19; GSW, 25; GSB, 15; BSG, 19; GM, 11; EGM, 5).  
About the solids, the one which showed the biggest methane yield per kilogram of volatile solids were the spent brewer's grains followed by the solid waste from gin production. Grape marc also showed good behavior though inferior to the previous substrates, due to the high content of lignin (which cannot be digested in anaerobic treatment) of this type of waste [28]. Exhausted grape marc was the less productive substrate in terms of biogas production. This could be expected since most sugars and other compounds found in the marc previous to fermentation and distillation, have been transformed into ethanol and other compounds and extracted in the spirit making process.  
Pot ale, while being a substrate created in large amounts in spirit making, has not been the subject of extensive research. [PERSON] et al. [29] reported a value of 554 L CH\({}_{4}\) kg\({}^{-1}\) vs. for pot ale in batch tests, which fits very well with the attained results in this work of 542 L CH\({}_{4}\) kg\({}^{-1}\) VS.  
The attained values for brewer's spent grains of 322 L CH\({}_{4}\) kg\({}^{-1}\) VS, are placed in the fork between those reported in [PERSON] et al. [30] of 429 L CH\({}_{4}\) kg\({}^{-1}\) vs. and similar to those in [PERSON] et al. [31] of 409.8 L CH\({}_{4}\) kg\({}^{-1}\) vs. and [PERSON] et al. [32] with 301 \(\pm\) 5 L CH\({}_{4}\) kg\({}^{-1}\) VS. The latter gives, as well, a value for trub and used yeast of 515 \(\pm\) 4 L CH\({}_{4}\) kg\({}^{-1}\) VS, inferior to the 578 L CH\({}_{4}\) kg\({}^{-1}\) vs. attained in the present study.  
About grape marc, the relatively modest values of 206 L\({}_{\rm N}\) CH\({}_{4}\) kg VS\({}^{-1}\) attained in the tests are quite superior to those reported in [PERSON] et al. [33] of 116 L\({}_{\rm N}\) CH\({}_{4}\) kg VS\({}^{-1}\) and similar to those in [PERSON] et al. [34], reporting figures of 252 \(\pm\) 35 L\({}_{\rm N}\) CH\({}_{4}\) kg VS\({}^{-1}\) but are inferior to those found in [PERSON] et al. [35] of 273.08 L\({}_{\rm N}\) CH\({}_{4}\) kg VS\({}^{-1}\) for grape marc used in white wine production or the ones attained by [PERSON] et al. [36] of 347\(-\)360 L\({}_{\rm N}\) CH\({}_{4}\) kg VS\({}^{-1}\). This may be related to the varietal characteristics of the grapes grown in the region and their own cultivation characteristics associated with a regional climate in which the production of sugars in the fruit at the time of ripening tends to reach low maximization levels.  
No values have been found in the available literature for the biomethanogenic potential of exhausted grape marc or for spent wash and solid spent botanicals and aromatics from gin production (aside from other works from the authors [37], where 699.54 L\({}_{\rm N}\) CH\({}_{4}\) kg VS\({}^{-1}\) were obtained for gin spent wash). So the values of 148, 727 and 281 L\({}_{\rm N}\) CH\({}_{4}\) kg VS\({}^{-1}\) obtained cannot be compared with any results from previous studies from other authors.