Oat bran concentrate (OBC) was defatted by supercritical carbon dioxide, pin-milled and air-classified into five fractions (<15, 15–18, 18–24, 24–30 and > 30 μm). β-glucan content (% dry weight) of defatted OBC, its subsequent pin-milling and the air-classified fractions in ascending particle size was 14.3, 17.0, 4.3, 5.8, 12.6, 14.7 and 22.4, respectively. High-performance size-exclusion chromatography equipped with multi-angle laser-light scattering and refractive index detectors showed that amylopectin was the predominant molecule present in all OBC powders but was present in greater concentration in fractions collected that were < 24 μm. Fractions >24 μm, which had the highest β-glucan contents had higher starch gelatinisation temperatures (measured using differential scanning calorimeter), and had substantially higher peak, breakdown, final and setback paste viscosity (measured using Rapid Visco Analyser, Foss North America, Eden Prairie, MN, USA) compared with the other lower-β-glucan containing fractions. No differences in water retention of 25% (w/w) oat powders in water (measured using thermogravimetric analyser) were observed among defatted OBC, its subsequent pin-milling and the five fractions separated by air-classification. In particular, differences in pasting properties show that defatted, pin-milled OBC that is fractionated by air-classification will have different food applications depending on particle size collected.