Rate of `dark progression' (see text) as a function of temperature in thaumatin crystals (from Warkentin et al., 2011, with additional data at T = 260 K and 300 K). The line is a fit to a thermally activated model with an activation energy of 14.8 kJ mol−1. Agreement between this energy and that for the high-temperature regime in Fig. 1 suggests that the underlying processes are similar. The inset schematically illustrates how the interrupted dose curves used to measure dark progression were measured (see text). From Warkentin et al. (2011), with additional data at 260 K and 300 K.