The Rheology of Caramel

Caramel is an emulsion of a dispersed phase of fat droplets stabilized by milk proteins in an aqueous amorphous sugar matrix containing products of caramelization and Maillard reaction. The processing of caramel in an industrial scale has many problems related to its rheology. In particular tailing and cold flow are undesirable effects. The rheology of caramel was studied as a function of processing temperature and hydrocolloid addition. Both rotational and capillary techniques were used. Caramel without added hydrocolloids had behavior which was close to a Newtonian liquid. Incorporation of the hydrocolloids carrageenan and gellan gum into the caramel made the material non-Newtonian and elastic. The latter was seen for both the oscillation and creep responses. Glass transition temperatures were measured by differential scanning calorimetry and calculated from the temperature dependence of the shift factors used to superimpose the oscillatory rheological data. Generally there was agreement between the two approaches although for some gellan gum containing samples the rheological Tg was about 10ºC higher than the DSC value.