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Brewers’ spent grain (BSG) is the primary by-product of beer production, and its potential use in food products is largely dependent on its processing, given its moisture content of up to 80%. This study aimed to evaluate the effects of physical separation with ultrasound application on the color, total phenolic content (TPC), antioxidant activity, proximate composition, total dietary fibers, and particle size distribution of BSG powders. Wet BSG (W) was subjected to two processes: one without ultrasound (A) and one with ultrasound (B). Both processes included pressing, convective air-drying, sieving, fraction separation (A1 and B1 as coarse with particles ≥ 2.36 mm; A2 and B2 as fine with particles < 2.36 mm), and milling. The total color difference compared to W increased through both processes, ranging from 1.1 (B1 vs. A1) to 5.7 (B1 vs. A2). There was no significant difference in TPC, but process B powders, particularly B2, showed lower antioxidant activity against ABTS•+, likely due to the release of antioxidant compounds into the liquid fraction during pressing after ultrasound treatment. Nonetheless, process B powders exhibited a higher content of soluble dietary fibers. In conclusion, ultrasound application shows potential for further extraction of soluble fibers. However, process A might be more practical for industrial and craft brewers. Further studies on the use of the resulting BSG powders as food ingredients are recommended.