Classroom demonstrations are a great vehicle for getting students to apply information they have heard in a lecture. Educational research is replete with data showing that concept application in an inquiry setting reinforces long-term science content retention. This means that students learn best when they experience applications of concepts and facts taught in science lectures. This article describes a demonstration that uses simple fruit and vegetable spoilage biochemistry principles to teach scientific reasoning skills. It is applicable to general biology students after they have had introductory lessons on the molecules of life. The demonstration can also be used as a review for students in upper-level biochemistry and organic chemistry. This demonstration has been used to supplement lectures covering enzymology, metabolism, protein structure, and scientific inquiry. The demonstration was recently used in a service learning situation in which college students taught elementary school students the principles of fruit and vegetable preservation. (Contains 1 figure.)