An apparatus for the study of the "spontaneous" heat production in stored organic materials has been described. Experiments with commercial cornmeal and cracked yellow field corn have shown that temperatures above 60° C. can readily be produced under suitable conditions of moisture content, oxygen supply and insulation, and that marked heating does not take place in the absence of oxygen. "Spontaneous" heat production is the result of oxidative reactions and will not take place to any marked extent in the absence of air or oxygen. Stored organic materials will not heat if retained under anaerobic conditions.