Assume for a minute you are inspecting a load of lettuce. You come across some heads (See image below) that have a distinct discoloration affecting the veins and midribs. One thing you know for certain is the discoloration definitely materially affects the appearance of the head, thus you would score it as a defect.
But what is this defect called? This picture was sent to me from a person training to be a fruit and vegetable inspector in South Korea. Although I only have a few pictures to view, it appears this inspector-in-training may have found lettuce affected with a defect called Rusty Brown Discoloration. The cause of this defect is unknown, but has been found in lettuce grown in Arizona or California. This defect is not commonly found, and I would venture to guess most of the younger USDA inspectors have never seen this defect in their careers. I have seen Rusty Brown Discoloration only a few times during my 30 plus years, and I have yet to come across it during the past 15 years.
Again, because I only have a picture to go by, I am not 100% sure this lettuce is affected by Rusty Brown Discoloration, but the symptoms make it highly likely. The discoloration will affect the midribs and veins and will eventually cover the entire crown. The discoloration spreads quickly on the head, and is always scored as a serious defect. The U.S. No. 1 Grade for Lettuce only allows 6% serious damage defects.
Shown above is the official USDA visual aid depicting Rusty Brown Discoloration. This visual aid was developed in 1970. Please share your thoughts if you have seen this defect recently, as everyone would enjoy hearing the comments associated with this defect.