An edible, hardenable coating composition is disclosed which comprises high levels of low viscosity propylene glycol alginate and a surfactant, which may additionally contain a filler, a pigment and optionally a small amount of a secondary film former and/or a strengthening polymer. The coating composition of the present invention may be applied to pharmaceutical and veterinary solid dosage forms, confectionery, seeds, animal feed, fertilizers, pesticide tablets, and foods and provides an elegant prompt release coating which does not retard the release of active ingredients from the coated substrate.