In aqueous media, anthocyanins are present under different forms in equilibrium, including red and violet pigment species and colourless hydrated forms. The latter predominate at mildly acidic ph values such as encountered in plant cell vacuoles and in wine. However, the anthocyanin pigmented forms stack vertically with other species present in the solution (co-pigments) to form complexes from which water is excluded. This results in enhanced colour intensity due to a shift of the balance from the colourless hydrated forms towards the dehydrated pigment forms involved in these stable complexes. The role of co-pigmentation in wine colour can be estimated by comparing red colour intensity before and after disruption of co-pigmentation complexes by dilution in a wine-like buffer. Co-pigmentation has been reported to account for 30 to 50% of the colour of young red wines, on the basis of such measurements.