I work for a lemon exporter company in Mexico, our technicians use a pressure tester on lemons but we have not found any information about the recommended levels of pressure on lemons. I was wondering if you could help us with that information that is so important for us. (F.)
A pressure tester may be used to determine the force required to release essential oils from the flavedo (outermost layer) of citrus fruits in the orchard to determine optimal time to harvest the fruits. If the fruits are very turgid (full of liquid), the essential oils from the flavedo can be released with lower force than if the fruits were less turgid. These released oils can damage the skin tissues and result in oil spotting ( green spots on the lemon). The solution is to wait until later in the morning when the fruits have lost some of their water content before harvesting.
Published research indicates that lemons should not be harvested if the force to release essential oils from their flavedo is below 29 Newtons (about 6 pounds-force) measured with a pressure tester with a 5mm (3/16 inch) rounded tip.
Reference: Cahoon, G.A., B.L. Grover, and I.L. Eaks. 1964. Cause and control of oleocellosis on lemons. Proceedings of the American society for Horticultural Science 84:188- 198. --Adel A. Kader