How to measure the moisture content of green coffee

Janice Kanniah
May 25, 2021
green coffee

No matter how much skill you have as a specialty roaster, you will always be limited by the quality of your green beans. If the beans arrive damaged, mouldy, or with any other defects, it could seriously affect the final flavour of the coffee and turn customers away from your brand.

One of the most important things to check when assessing green beans is moisture content. Typically making up around 11% of green coffee’s weight, it can influence a range of characteristics, from acidity and sweetness, to aroma and mouthfeel.

For specialty roasters, learning how to measure the moisture content of green beans is crucial to roasting the best coffee possible. Not only will it help root out defects in a large batch of beans, it will also aid key variables during the roast, such as charge temperature and development time.

To find out about measuring moisture content in green coffee beans, I spoke with 2019 World Cup Tasters Champion and Sumo Coffee Roasters founder, Daniel Horbat.

Read next: How Can Roasters Control The Ageing Of Green & Roasted Coffee?

green coffee beans

What is green coffee moisture content and why does it fluctuate?

A ripe, freshly harvested green bean typically has between 45% and 55% moisture content. After being dried and processed, it will usually fall to around 10-12% depending on the technique, climate, and length of time spent drying. 

According to the International Coffee Organization (ICO), the ideal moisture content of green beans ready for roasting should be between 8% and 12.5%.

This range is generally considered the optimum for factors such as cup quality, the degradation rate of green coffee during storage, and the risk of microbial growth. That being said, some coffees, like India’s Monsoon Malabar, tend to perform better in the cup with higher moisture contents.

Once green beans have been processed and prepared for shipping, they will usually be placed in jute sacks to maximise air circulation during transit. However, coffee beans are naturally hygroscopic, meaning they absorb moisture from the air, the moisture content can easily fluctuate between origin and roastery.

Changes to humidity or exposure to sunlight either during transport or storage could affect the moisture content of coffee. Therefore, to ensure consistency and avoid surprises further down the line, it should be checked at regular intervals, including pre-shipment and arrival.

moisture content green beans

Why is it important to track green coffee moisture changes?

When green beans are roasted, all the flavours and aromas locked inside the coffee are brought out. However, in order to unlock the full potential of the green beans, it’s important that specialty roasters are first able to measure their moisture content.

Daniel Horbat opened his own roastery in Dublin in 2019 after being crowned World Cup Tasters Champion. He tells me that a coffee’s moisture content informs roasters as to how they should approach a roast if they are to achieve their desired roast profile.

“If a bean has too little moisture and you’re too aggressive, it will roast faster on the outside while the inside of the bean remains raw,” he explains. “This will result in grassy notes. On the other hand, if you use a slow roasting process you’ll end up with baked notes.

“A coffee with the right moisture content will usually be more vibrant in flavour with balanced acidity and will stand out more on the cupping table compared to coffee with low moisture content.”

According to coffee roasting expert Scott Rao, the reason for this is because water slows heat transfer within beans and requires extra heat input to evaporate. Hence, roasting very moist beans requires extra energy, both through longer roasting time and higher heat.

As well as informing the roast itself, moisture content can also influence the total costs of production for specialty roasters. This is owing to the fact that roasters typically pay for green coffee by weight. If, for example, 12% of the coffee is made up of moisture which will burn off during the roast, this could accumulate over time.

To reduce costs and maximise profits, some roasters may opt for green beans with lower moisture content. But it’s difficult to know this without measuring the coffee beforehand.

coffee beans

How to measure the moisture content of green coffee

Several methods of measuring the moisture content of green coffee exist, with some more popular than others. Perhaps the most traditional is the oven drying method, in which a sample of green beans are baked at 105°C (220°F) in a convection oven for 24 hours and the weight loss is recorded. Naturally, this method relies on accurate scales and consistency across all recorded batches.

Daniel recommends investing in an electric moisture analyser, and tells me that, it’s “an extremely important device to have in a roastery”.

Most modern moisture testers can automatically gauge green coffee moisture content in seconds. It can be backed up to your computer, allowing you to track results without the need for thermometers or charts. While expensive, it can save you money in the long run by avoiding the costs of running an oven overnight and using up valuable green beans.

sustainable coffee packaging

How does coffee packaging impact green coffee moisture levels?

The moisture content of green coffee beans can change during storage, much in the same way that it can change during transit.

To avoid this, Daniel says that the bags used to package green coffee should prevent unnecessary moisture changes. He tells me that this is especially important for green coffee intended for consumers, specifically home roasters.

“When exposed to humid conditions, coffee reabsorbs moisture,” he says. “Condensation often occurs when coffee moves from a warm climate to a cold one. This is why hermetic bags and/or lined containers play an important role in maintaining moisture content. I recommend using airtight bags or vacuum packaging.”

The materials used to package green coffee must be durable and easy to handle, pack, and stack during storage. It should protect the coffee from moisture and contamination by being airtight and resealable. Once filled, vacuum sealing can provide extra protection by removing all internal air.

Selecting the right packaging for your green coffee will keep it in good shape until it is roasted or sent off to the consumer.

moisture content coffee

At MTPak Coffee, we offer a range of sustainable coffee packaging for both roasted and green coffee beans. We can help you across every step of the process from concept and design, to printing and manufacturing.

For more information on our sustainable coffee packaging, contact our team here.

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