Peptization or deflocculation is the process of converting a precipitate into a colloid by stirring it with a suitable electrolyte called a peptizing agent.[1]​.

This is particularly important in colloidal chemistry or for precipitation reactions in an aqueous solution.[1]​ When colloidal particles have an electrical charge of the same sign, they repel each other and cannot aggregate. Freshly precipitated iron or aluminum hydroxide is extremely difficult to filter because the very fine colloidal particles pass directly through a paper filter. To facilitate filtration, the colloidal suspension must first be flocculated by adding a concentrated salt solution to the system. Multivalent cations are more efficient flocculants than monovalent cations: AlCl > CaCl > NaCl. The electrical charges present on the surface of the particles are "neutralized" and disappear. More correctly speaking, the electrical double layer existing on the surface of the particles is compressed by the added electrolyte and collapses at high ionic strength. Electrical repulsion no longer prevents the aggregation of particles and they can then coalesce "Coalescence (chemistry)") to form a flocculent precipitate that is easy to filter. If the precipitate is washed with an excessive volume of deionized water, the electrical double layer present on the surface of the particles expands again and the electrical repulsion reappears: the precipitate becomes peptized and the particles pass through the filter again.