Last week we got a comment on our post “Coffee Testing: What We Look For and Why“:
Moisture content in green coffee is an indicator of freshness, proper processing at the coffee mills, and proper storage conditions.
Coffee is hygroscopic—that is, it attracts and hold water in moist environments and will release water in dry environments.
Fresh green coffee upon import should be between 10% and 12% moisture for washed coffee, and up to 13% moisture for naturally processed coffees and coffees from Indonesia. The National Federation of Coffee Growers of Colombia has a regulation limiting Colombia coffee moisture content to below 12% upon export.
Green coffee moisture will affect cup quality: Beans with high moisture content may discolor and turn light opaque during storage. High moisture content coffee may have cup quality issues as well, ranging from fruity to sour, and possibly ferment. Beans with low moisture will lose their green color and turn pale yellow quickly, with cup quality issues of flat, papery, thin and cereal characters.
Green coffee moisture will effect blend development: Variations in green coffee moisture will affect the roasting process and change the dynamics of the roast profile.
High moisture content beans will roast slower, requiring additional energy to dry the beans before Maillard reactions / non-enzymatic browning may occur.
Low moisture levels are necessary to allow coffee’s internal temperature to reach around 154 C (309 F) to begin. Low moisture contents will cause the profile roast to speed up, with higher temperatures realized earlier, creating a faster roast.