Measuring Coffee Bean Moisture Content

Abstract

Why measure coffee bean moisture content? The amount of moisture in coffee parchment and beans is important for two reasons: (1) coffee that is too high or too low in moisture will not maintain high cupping quality, and (2) you are trading in coffee, not water. Green coffee that is high in moisture (greater than 12 percent wet basis) can deteriorate due to bacteria, mold, or yeast, especially if the seed is killed. If the seed re­ mains alive, enzymatic activity will cause the cupping quality to change. In any case, the parchment coffee moisture level should be lowered to below 12 percent soon after harvest. When the ambient relative humidity is about 70 per­ cent, coffee beans will gradually equilibrate to about 12 percent moisture. Thus green bean coffee is generally dried to 12 percent, and bought and sold at this moisture percentage. If the bean dries to below 9 percent moisture, it will shrink enough to become distorted, which will give the appearance of low-quality coffee. To meet the Hawai‘i Department of Agriculture stan­ dards for coffee (see www.hawaiiag.org/hdoa/admin­ rules.htm), the moisture level must be between 9 and 12 percent, ± 0.3 percentage points. Coffee of consistent quality commands a higher price. The range for maintaining quality is quite broad, making it easier to know the coffee is at the correct moisture. Precisely knowing the coffee is at 12 percent moisture is not necessary except in the market. Knowing the coffee is between 12 and 9 percent moisture at all times after it is dried is important to ensuring that your coffee has the best quality at the time of sale. A deviation of one percentage point from 12 percent moisture content represents 1 pound of water per 100-lb bag; at 11 percent moisture, you need an extra pound of coffee to make the 100 pounds. Depending on the number of bags and the price of coffee, not knowing the correct moisture content can lead to quite a bit of money at issue.