Agricultural activity contributes actively to global warming by emitting greenhouse gases (GHGs) such as methane (CH4), being ruminants one of the main producers of this gas. On the other hand, there is excess of agro-industrial by-products such as grape pomace with a high polyphenolic concentration. Therefore, it is necessary to develop strategies to reduce both GHGs and agro-industrial residues. In this work, the use of the by-product grape pomace, rich in tannins, is proposed as a nutritional strategy to be incorporated in ruminant feed concentrates to reduce the production of ruminal CH4.For this, four grape pomaces Tempranillo variety (P1, P2, P3, P4) from different wineries, were added to a base concentrate such as barley at four levels (1.25%, 2.5%, 5% and 7.5%).These samples were fermented in vitro in two different periods of time (18 and 96 h). The kinetics of total gas and CH4 production were studied. A quantitative inhibitory effect was observed for both parameters when incorporating 7.5% grape pomace, as well as a variable qualitative effect depending on the fermentation time, being P3 the most effective pomace after 18 h and P2 after 96 h. Therefore, the incorporation of grape pomace in ruminant fattening feed could represent an alternative to the environmental problems of the agricultural sector within a green and circular economy model.