Defoamer compositions are described and the use of defoamer compositions in paper and pulp mills is described, especially for use at the brown stock washing steps in a pulp mill. The defoamer composition comprises: a) about 20 wt % to about 90 wt % of at least one organophosphorous component (e.g., compound or polymer, n-tributoxyethyl phosphate); b) about 1 wt % to about 10 wt % of at least one silane treated silica; c) about 0.5 wt % to about 10 wt % of at least one surfactant that is anionic or non-ionic; and d) optionally, water or an aqueous liquid.