An in vitro study was conducted to investigate the effects of soybean meal (SBM) treated with two commercially available quebracho (QUE) and chestnut wood (CWE) extracts, at three different concentrations (15, 30 and 60 g/kg SBM) on the extent and rate of gas and short-chain fatty acid (SCFA) production. During the incubation, the gas production was measured at regular intervals from 0 to 48 h and the data were fitted with the Gompertz model to model gas production dynamics. After 24 h volumes of two syringes per substrate were analysed for individual SCFA contents. Treatment of SBM with CWE and QUE at the lowest concentration significantly increased (P < 0.05) gas production at 24 h of incubation (Gas24) and total SCFA production, but did not affect the proportions of individual SCFA. At higher concentrations (30 and 60 g/kg SBM), only the CWE significantly decreased (P < 0.05) Gas24, while both tannins significantly decreased (P < 0.05) the maximum fermentation rate. Both higher concentrations of CWE and QUE also did not affect total SCFA production, yet CWE significantly increased (P < 0.05) the proportion of acetic acid, while QUE tannins did not affect the proportions of individual SCFA. Obtained results suggest that the low doses of QUE and CWE have a stimulating effect on rumen microorganisms, enhancing the extent and rate of fermentation, while higher doses of CWE and QUE decrease the rate of fermentation; however, only CWE affects the fermentation pattern of rumen microorganisms by changing the proportions of individual SCFA.