Earlier studies indicated that the activity in the initial phase of composting may be reduced when the temperature rises too fast under low pH conditions. A compost reactor experiment on household waste was designed to test whether the degradation time could be reduced by actively preventing the temperature from rising until the pH had reached a certain value. This experiment was performed by monitoring pH in the condensate from the cooled compost gas. The results from 3 + 3 runs with and without temperature control confirmed our hypothesis and a considerable reduction in composting time was achieved. One possible explanation for the results is that the microbes active in the low pH phase are hampered by high temperature, The abrupt rise in pH when the fatty acids are consumed seems to be a good marker of the point when temperature control can be discontinued.