Roasting Science

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Bean Properties

RS 2.02 Moisture Content

Moisture content is one of the most important properties of green beans. Moisture is an important variable in green coffee at all stages in the supply chain, from producers and traders to roasters.

For producers and traders, the moisture content is critical to the coffee’s quality because it affects the bean’s shelf life. The International Coffee Organization (ICO) specifies that all coffee for export must contain 8.0–12.5% moisture (ICO 2021).

If beans are stored at a moisture content higher than 12.5%, their quality fades much more quickly. On the other hand, if the beans are dried too much, their colour and flavour can be irreversibly damaged (Rojas 2004). Parchment coffee with a moisture content below 9–10% is also much more likely to break during hulling (Brando 2004). We will explore the effects of moisture and humidity on green coffee storage in more detail in Lesson 2.06.

Drying coffee more than is necessary for storage is also disadvantageous to producers and traders because it reduces the total weight of the beans. For large quantities of coffee, a percentage point difference in the moisture content can have a big financial impact (Gautz et al 2008).

For roasters, the moisture content is one of the biggest factors that determines how much energy is needed to achieve a particular roasting profile (Nogueira and Koziorowski 2019). The moisture content also has an effect on heat transfer, and it represents the major part of the mass lost during roasting. 

For all these reasons, it’s important to be able to track moisture content in green coffee easily and accurately.


Measuring Moisture Content

The international standard method for measuring moisture content of green coffee is oven drying. This method is time consuming but should be used as the reference for calibrating all other measurement devices (ISO 2012). A specialised dehydrator oven with controlled airflow and precise control of the temperature will give the most accurate results.