Moisture Content in Green Coffee

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.

5 comments to Moisture Content in Green Coffee

  • How does low moisture content (below 9%) effects on coffee cup quality?

  • Hello Oleg:

    Thank you for your question. Green coffee beans with low moisture levels will roast faster since there is less water to evaporate at the start of the cooking process.

    In coffee, the flavor is a combination of Maillard reactions and caramelization. However caramelization only takes places above 282-302 degrees F (120-150 degrees C) The Maillard Reaction is non enzymatic browning resulting from a chemical reaction between an amino acid and reducing sugar, usually requiring heat. In coffee, it starts around 309 degrees F (154 degrees C).

    Controlling when the green coffee beans begin caramelization and the Maillard reaction as part of the time and temperature profile is the skill of the roaster for the primary development of flavor.

    Charring occurs as a coffee continues to lose moisture and gain heat and is characteristic of dry distillation.

    Low moister coffees will roast fast and hot and develop roast defects like scorching and tipping more easily. Also, these coffees may present flat, malty, baked, or papery sensory characters.

    Please let us know if you have any follow-up questions.

  • avatar Pedro

    Thus, can I say that controlling the moisture content of green coffee is one of the way to maintain the quality of the green coffee?

  • Hello Pedro – Yes, managing moisture in coffee is an important factor in preserving and maintaining quality.

  • avatar Mike

    I’ve stored my green beans in 5gallon buckets, they are about 2yrs old now. The last year they have begun to taste burnt when I roast them. I roast them the same, no other factors have changed except age of the beans. Could this be due to low moisture content or have the flavor compounds in the bean deteriorated? If due to low moisture, is it feasible to moisturize them before roasting or has the damage been done due to long term non ideal storage?

    thank you

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