Four coffee varieties in separate bean trays. Each has label corresponding to type, the Robusta, Arabica, Liberica and Excela.
Notice the coffee colors. The normal color should look like this…
Arabica is the whitest of them all. Liberica is darker than normal, Excelsa even darker and Robusta is the darkest.
What are the possible causes of color changes?
The white color of Arabica. I found the answer from sweetmarias.com. Green coffee beans should have 12% moisture content. Moisture re-absorption up to 13% causes bleaching, the whitening, and loss of many desirable properties.
I found no possible explanation for darker green bean colors or the darkening during storage. Maybe, darkening is caused by dirt adhering to bean surface! Dirt from storage sack and warehouse. Your inputs will be appreciated.
Stored and sometimes discolored coffee beans are locally called as laon or simply old coffee. Usually taste better than newer (unverified claim).
This phenomenon is synonymous to santunis, rambutan, yakon and singkamas. These commodities are best eaten several days or weeks after harvest. They are becoming sweeter and yummier as day pass by.