Water Activity Meters

Water Activity Meters

Water activity is one of the most important - and often overlooked - factors in green coffee quality. Measuring it helps you spot risks early, from flavour staling to mould growth. These devices give you fast, reliable readings so you can store and manage green coffee more confidently. Designed for both lab and field use, they’re built for anyone working with coffee in its raw form.

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Your guide to Water Activity Meters

  • What is water activity, and why does it matter in green coffee?

    Water activity (aw) measures how much water in green coffee is available for chemical reactions. It’s not the same as moisture content - which tells you how much water is present overall - but rather how active that water is. Too high, and the coffee can develop mould or degrade faster. Too low, and you risk flat, lifeless flavours when roasted.

  • What’s the ideal range for green coffee?

    Between 0.45 and 0.55 aw. Above 0.55, you’re inviting microbial growth and chemical instability. Below 0.45, the coffee loses its vitality - enzyme activity drops, the beans go brittle, and flavours fade. Staying in that stable mid-range helps preserve cup quality and ageing potential.

  • When should I measure water activity?

    It’s most useful after drying, before export, and any time coffee has been moved or stored in changing conditions. Because water activity is sensitive to temperature and humidity, regular checks give you a clearer picture of how green coffee is holding up - especially for longer-term storage or transport.

Your questions, answered

Is water activity the same as moisture content?

No - moisture content tells you how much water is in the coffee by weight. Water activity measures how much of that water is “free” and available to drive chemical reactions. Both matter, but they’re not interchangeable.

Why does low water activity cause flat-tasting coffee?

When water activity drops too low (below 0.45 aw), the enzymes inside green coffee stop working properly. That affects how the coffee develops during roasting - often leading to muted, dull, or stale flavours in the cup.

What happens if water activity is too high?

High water activity (above 0.55 aw) increases the risk of mould, bacteria, and flavour instability. Coffee stored at high aw will degrade faster, with off-notes and defects becoming more likely over time.

Can a stable moisture content guarantee stable water activity?

Not always. The two are related, but not directly correlated. A coffee can show a ‘safe’ moisture content but still have unstable water activity - especially if it’s been poorly dried or stored.

Who should be using a water activity meter?

These are essential tools for producers, exporters, and green buyers - anyone managing quality through drying, storage, or transit. They’re also useful for roasters storing coffee for long periods or troubleshooting cup quality issues.