Ultraviolet light is useful to see problems with coffee like mold and bacteria, but these are things that affect low grade lots that are already quite damaged. However, when I suspect drying problems with coffee, I check it out anyway. Some recent Sulawesi wet-hulled lots have been very surprising under UV light, and in general UV shows the problems with the wet-hull process overall (although our Blue Batak Sumatras fare well under UV light. This was a surprise. An Ecuador
Cariamanga lot with a nice cup, but some odd off notes cropping up way too often. The green coffee loots PERFECT. But under UV light, small nicks, little marks were I suspect the pulper scraped against the coffee seed due to misadjustment. Then in fermentation the damaged areas are in contact with mucilage and bacteria, rather than being protected by the parchment layer. The result is some off cups, but mysterious since there was little clue under normal light. I
could not get the coffee to "light up" completely under UV for the photo so the arrows assist in seeing the glowing areas, and then the 1 little pulper kiss marks can be seen.