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Control water activity to prevent green coffee from mold


Water activity is considered by the Specialty Coffee Association (SCA) to be an important parameter related to the quality of green coffee. It can shorten the freshness time and cause unpleasant flavors or mold in coffee beans if they exceed certain limits. What is the ideal water activity level? How to control it? Let’s find out with 43 Factory Coffee!


What does water activity mean?


Water activity is the ratio of the vapor pressure of water in a substance to the vapor pressure of pure water (under the same temperature and standard conditions). Simply put, water activity is the chemical content of water in a substance (can be green coffee beans, or roasted coffee beans). This amount of water exists in that substance but is not bound to any components or compounds, but can freely participate in chemical reactions.

Water activity is measured on a scale from 0.0 to 1.0 in aw units. Of which 1.0aw is pure water. Any substance other than pure water will have a water activity of less than 1.0. High water activity means that the substance contains a lot of water for chemical reactions and vice versa.

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Ideal water activity ratio for green coffee


According to DCN research, the optimal water activity for green coffee is from 0.45aw – 0.55aw. Under proper storage conditions, coffee at this level will maintain its quality for at least 6 to 8 months or even longer. In fact, a water activity of  0.50aw is the ideal point. If not affected by environmental factors, these coffee beans can retain their quality for at least 18 months. If green coffee beans have a water activity below 0.45 aw, they will become dry, leading to an aged flavor when roasting the coffee. The surface of green coffee beans can become harder and more brittle, leading to poor grinding performance and reduced flavor scores when cupping.

Because inside coffee beans there are hundreds of compounds and microorganisms that create scent and taste. Each microorganism will have a different water activity limit to maintain activity and growth. With mold, water activity at 0.70 aw will stop growth. Conversely, in this range, mold and mycotoxins can contaminate green coffee beans leading to a musty taste and odor. However, at water activities less than 0.55, green coffee beans will not support the growth of any microorganisms, so the ideal range is below 0.55 aw.

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Excessive water activity reduces the quality of green coffee


Green coffee beans are hygroscopic. It tends to absorb water from its surroundings. Therefore, water activity has a great influence on the quality of green coffee during storage. Coffee with high water activity will tend to absorb a lot of water, promoting substances to react with each other. The increased reaction rate in coffee beans causes the oxidation and decomposition of substances to become faster. The seeds will gradually lose their flavor and aroma while creating strange flavors and toxic substances. For example, a coffee with a score of 88 if it has a water activity higher than 0.5aw will lose many flavor points in just a few months. Green coffee beans will show Maillard browning (change in color and flavor), lipid oxidation, and rancidity.

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How to protect green coffee beans from the effects of water activity


Keeping the water activity of green coffee beans below 0.55 aw will slow down the rate of oxidation. Suppose the rate constants of these reactions under a number of different storage conditions can be determined. In that case, a prediction model can be used to estimate the time required for the reaction to reach unacceptable levels in any storage conditions. Therefore, to protect green coffee beans from the effects of water activity, it is necessary to ensure a proper coffee storage environment.

Green coffee beans need to be stored in sealed, waterproof, and water-resistant, sealed bags. Warehouse conditions always ensure a temperature between 60-70°F, humidity about 50%, avoid direct sunlight, and stay dry. Prepare tools that can measure water activity and moisture in coffee so you can control it optimally. In addition, avoid moving or suddenly changing the temperature or humidity of the coffee storage warehouse.

Cà phê nhân xanh đông lạnh

Controlling water activity not only helps coffee retain its flavor but also keeps it fresh longer. Therefore, to keep your coffee delicious, monitor and store it in the ideal water activity!

Don’t forget to follow 43 Factory Coffee Roaster’s news channel to discover useful information!

In addition, you can visit XLIII Coffee – the brand developed from the predecessor 43 Factory Coffee Roaster to enjoy high-quality specialty coffee imported directly from famous growing areas.

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