A method was developed to investigate the effect of shrinkage on the temperature rise in evacuated mushrooms during blanching. Mushrooms were heated or cooled applying (I) two temperature regimes in which no shrinkage took place, and (2) two temperature regimes in which substantial shrinkage took place. The threshold temperature T-thr at which shrinkage started was determined to be +/-45 degrees C. Shrinkage caused a 1.5-2-fold increase in the rate constant for the temperature increase in the centre of the mushroom. The rate constant of the temperature change for the non-shrinking mushrooms followed the theory for the temperature rise in a sphere, when using the thermal properties of water and the characteristic radius of 0.9 times the equivalent radius.