The mechanism of aggregation in triglyceride oil-in-water (o/w) emulsions in which the droplets contain fat crystals was investigated . As a surfactant either sodium dodecyl sulphate (SDS) or a protein was used . The crystals must be situated at the o/w interface to cause partial coalescence ; if the fat crystals are totally wetted by either the oil or the aqueous phase they do not affect emulsion stability . Although a suitable contact angle (crystal, oil, aqueous phase) appears necessary for partial coalescence to occur, it is obviously not a sufficient condition . Additional conditions are a close enough approach of the globules, allowing the protruding crystals to bridge the aqueous film between the globules, and the presence of sufficient solid fat . Crystals may have an approximately radial orientation at the o/w interface if they are kept in a continuous fat network . If, furthermore, the contact angle (as measured in the aqueous phase) is about 90`, the coalescence efficiency a was high (mostly a'> 10 "). If crystals can move around freely in the oil droplet, they can obtain a tangential orientation at the interface irrespective of the contact angle . Such globules are not very sensitive to partial coalescence (a x 10 -s or less) . Even if partial coalescence had already occurred, it could in some cases be undone by changing the wetting properties so that the fat crystals become separated from the interface . This reversibility only held if the change occurred within a few hours after aggregation . After that the partially coalesced emulsion droplets had irreversibly merged into one bigger clump.