Fresh coffee is transmissible to red light, but as the coffee becomes stale, the organic compounds degrade and the brew becomes less transmissible to the light. To monitor coffee freshness, a beam of light is passed through a transparent coffee pot and the transmissibility of the brew is displayed as...http://www.google.com/patents/US5956151?utm_source=gb-gplus-sharePatent US5956151 - Beverage freshness monitor
