Measures the free, biologically-available water in the bean on a 0–1 scale — a better predictor of shelf life and stability than moisture content alone.
•Measured with a dedicated water activity meter.
•Ideal storage range is generally about 0.45–0.55 aw.
•Above this range increases the risk of mould and faster quality loss.
•Below it, beans can lose vitality, turning brittle with a flatter roasted flavour.
