Novel techniques to measure the interactions between liquid triglycerides and solid crystals have been developed. These methods involve the radio-labelling and detection of triglyceride molecules. They enable rates of reactions to be monitored in real time. Thus reaction mechanisms can be deduced. The techniques can be used to investigate processes such as crystallisation and dissolution under varying conditions. In this paper measurement of crystallisation and dissolution reactions in a semi-solid fat matrix with tripalmitin crystals and tripalmitin in solution is described. The reaction has been shown to be first-order over a wide range of temperatures. Further, the reaction has been shown to be strongly controlled by the rate of diffusion of the liquid tripalmitin molecules.