Comparison of the residence time distributions of water and milk in an experimental UHT sterilizer

The residence time distributions (RTD) of water and milk in an experimental direct-heating UHT plant of the infuser type were measured at the same mean residence time using a dye tracer. Results showed that milk had a broader RTD than water, with minimum residence times of 1·0 s and 1·5 s and σ_t² values of 2·19±0·23 and 1·08±0·18, respectively. The effect of the broader RTD on the sterilization efficiency of the plant is discussed, together with possible reasons for this difference.