Heat treatment of oat grain had signiÐcant e †ects on the viscosity of Ñour slurries. Steamed oats produced highly viscous Ñour slurries, whose viscosity increased with time, whereas the viscosity of Ñour slurries produced from raw or roasted (104¡C for 120 min) oats was much lower and degraded rapidly. Slurry viscosity was correlated with (1 ] 3), (1 ] 4)-b-D-glucan concentration in the Ñours and treatment of slurries with lichinase lowered viscosity signiÐcantly. E †ects of steaming were partially reversed by roasting treatment and vice versa. Mixtures of equal amounts of raw and steamed Ñour resulted in slurries more viscous than either Ñour alone, but that viscosity degraded after 3 h to less than the mean viscosity of the steamed and raw controls. Water-soluble extracts from steamed Ñour had about twice the viscosity of raw or roasted Ñour extracts, but contained only 80% of the (1 ] 3), (1 ] 4)-b-D-glucan present in those extracts. Molecular weight analysis of soluble carbohydrates from raw, roasted and steamed soluble extracts indicated the molecular weight of b-glucans in these extracts was similar. However, if extracts were made from slurries that had incubated for 3 h, extensive degradation of b-glucans was evident in raw and roasted samples. It is likely that enzymic degradation of (1 ] 3),(1 ] 4)-b-D-glucans is responsible for much of the decreased raw and roasted Ñour slurry viscosity over extended time periods, but di †erent heat treatments appear to also a †ect (1 ] 3), (1 ] 4)-b-D-glucan polymer interaction.