In this study, mixtures of ethanol–water (5–20% v/v) were used at high temperatures (135–175 °C) to extract β-glucan and phenolic compounds, in relatively short extraction times (15–55 min). This new approach allowed obtaining concentrated solutions rich in β-glucan and antioxidants to be used as food additives/ingredients. Based on our findings, a careful selection of the temperature and ethanol content must be done, since β-glucans and phenolic compounds behave in a completely opposite trend during the extraction. High temperatures and long extraction times (> 35 min) result in low concentrations of β-glucan and high phenolic content in the liquid extract. High temperatures tend to degrade the β-glucan, indicated by the low extraction yields with low molecular weight and the presence of sugar degradation compounds like HMF. However, mixtures of pressurized aqueous ethanol at high temperatures were useful to extract hydroxycinnamic acid, that are strongly bounded to lignin. The amount of ethanol used in this study was not statistically significant, as did not affect the extraction of any of the target compounds but decreased the fragmentation of β-glucan. To maximize both β-glucan extraction yield and phenolic content, it is necessary to work at mild conditions of 151 °C, 21 min and 16.8% of ethanol in the mixture in the range of process parameters evaluated in this study.