Fun with American DJ Black Lights!
While cupping through some coffees we were taking some moisture readings as well as UV readings by looking at the green coffee under black light. This is something we like to do and have talked about before because it can help show age in a coffee which will be noticeable as "glowing" edges which indicate some moisture loss.
Other defects that are not noticeable to the naked eye are also visible under UV light. While looking at one particular coffee we noticed full on glowing beans, which generally indicates a drying defect. There were a large number of these beans in this particular coffee, so we took a 300 gram sample and hand sorted through it to pick out all of the full on glowing beans in the sample.
We then set up two sample roasts; one of the cleaned/sorted coffee, and one that was loaded with the sorted out defects (which added up to a little under 10 grams) in order to see what the impact of this defect was on the cup. The samples were set up blind, but not a single cupper guessed wrong in identifying which sample was the tainted one. The sorted sample had brilliant acidity with a clean and sweet finish. The tainted batch had a very noticeable dryness and was very muddled throughout the cup and especially in the finish.
It is always very eye opening to not just try looking at your coffees literally in a new light, but to take the time to sort and then identify what the impact a defect might have on the cup. The original unsorted coffee itself (the tainted batch was a loaded batch in order to accentuate the defect) cupped pretty nicely with a lot of sweetness, but with just a little lack of clarity.