Polysaccharides are important in colloidal stabilization-destabilization phenomena. In a previous study, three different trends were observed upon addition of wine polysaccharides to procyanidin suspensions: rhamnogalacturonan II monomers had no impact, the MPO mannoprotein fraction strongly inhibited aggregation, and rhamnogalacturonan II dimers increased aggregation. After molecular weight fractionation of MPO mannoprotein, the molecular weight effect on polyphenol particle size was investigated. Low molecular weight macromolecules are the stabilizing species, while high molecular weight molecules have no impact in "standard" wine conditions (pH 3.4 buffers containing 2 gL(-1) tartaric acid and 12% ethanol). At high ionic strengths or low ethanol concentrations, all mannoprotein fractions prevented tannin aggregation and precipitation