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As pointed out here, my coffee powder seems to have caught moist. Since it is in a significant quantity and a very nice powder, I don't want to waste it. Is there any solution to this problem? The obvious one that came to my mind was heating it up on a low flame, but I don't know the pros and cons of it. Can someone help me with this?

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  • By coffee powder do you mean an instant coffee or perhaps a finely ground coffee? Heating probably makes sense, but an open flame would invite combustion. So I'd use other heat sources if available.
    – hardmath
    Jan 2, 2023 at 5:34
  • A finely ground coffee it is @hardmath. Which heating mechanism would you recommend?
    – Niranjan
    Jan 2, 2023 at 5:46
  • If it got moist, it's probably already too late. You can warm it to dehydrate it, but it's likely the flavor won't be the same. It's why the recommendation not to freeze coffee. Humidity in the container condenses, and if the container is opened while it's still cold, humidity in the air condenses on it. The moisture makes the coffee rapidly go stale. Worst case, mold can start to grow, which will give it a bad taste long before it's visible. Warming it to dehydrate it will also speed oxidation. But you've got nothing to lose. Try it and see if it's still drinkable. If so, use it up quickly.
    – fixer1234
    Jan 2, 2023 at 21:58
  • @fixer1234 I tried heating it up, you were right, there is a change in taste, but fortunately it isn't that big. I am happy that my coffee is saved :)
    – Niranjan
    Jan 3, 2023 at 12:19

2 Answers 2

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I'll take it as given that the problem you have comes from moisture in your finely ground coffee. Indeed studies show finely ground coffee, other variables being held constant, has a greater hygroscopic tendancy (absorbing moisture from the surroundings during storage) and a higher angle of repose α:

Angle of repose is useful in order to acquire information regarding solid flowability. According to Shittu & Lawal (2007), during powder reconstitution, water molecules that hydrate the product's surface tend to reduce cohesivity between particles, allowing a rapid water penetration; thus, powders that possess high angles of repose, have higher difficulty to incorporate water. All factors tested (roast level, grind size and storage time), and the interactions between them, significantly influenced the angle of repose (α).

I'll report the experiment that I did with removing moisture from used espresso coffee grounds by repeated microwaving. This is no guarantee that it will resolve the problem reported by the OP, where in an earlier Question South Indian filter not brewing properly it was said:

I don't know why, but suddenly it is taking longer to finish the brew and sometimes (mostly from the second time) the water doesn't even go down. It just stays in the upper part of the instrument.

This method of brewing is unfamiliar to me, and the description "to brew without using the middle small instrument which looks like the one used in a french press" sounds like it is akin to a pour over (the tag was used there and here).

The possibility of drying coffee grounds was dismissed in this previous Answer:

I wouldn’t attempt to dry wet grounds - the quality would likely suffer and for brewing they will be made wet again, which would make the drying step moot.

However there is perhaps something about the method of brewing at issue here that avoids these objections. So to proceed with the experiment:

experiment drying

On the left is a frozen portafilter basket with used espresso grounds, which presents something of a maximally moist batch of coffee grounds. I emptied the basket into a spare microwaveable dish (a creme brulee crock).

Setting my 1200W microwave to 30 seconds, I ran it and checked to see how hot or warm the dish and its contents became. In the first run the contents became noticeably steamy, but then heating declined (water is specifically absorbing of the microwave radiation). After a dozen runs the used grounds seemed to be contributing nothing to the warming of the dish (an empty crock by itself gets warmed but not hot in 30 seconds).

To the touch the grounds now feel dry, and as a test I put the dish in the freezer for 30 minutes. This produced no clumping or grounds sticking to the dish. So I'm going to say this was a quick and effective technique to dry the grounds per se, without resort to expensive desiccant supplies or DIY vaccum freeze drying equipment.

Finally we invoke the platitude that an ounce of prevention is worth a pound of cure: storing the fresh coffee ground in packaging that prevents moisture absorbtion is easier than trying to fix a problem later on.

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  • Thanks for the detailed answer, sorry I had missed it completely and hence the delay in accepting. I tried your method and it worked for me too.
    – Niranjan
    Mar 17, 2023 at 15:30
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If you're looking to get rid of the moisture in your coffee, then you can try one or more of the following methods. The first option is to pour your coffee into a glass jar and store it in a cool, dry place. This will help to reduce the amount of moisture that's present. Another method is to put ground coffee into an airtight container and store it in a sealed bag or container away from light. The high levels of carbon dioxide that are produced during storage will cause the water molecules within the grounds to break down, leading to decreased absorption of water by the beans. Finally, you could also try using an air drier.

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    Welcome, and thanks for weighing in. The points in the answer don't seem correct and I'm wondering if there's some documentation you could link to. For example, storing it in an air-tight container in a cool, dry place will prevent it from absorbing moisture from the air during storage but would lock in the existing moisture rather than dry it out. Freshly-roasted coffee releases some free carbon dioxide (the reason for the valve on the package), but that wouldn't be a factor with repackaging older coffee. Also the CO2 doesn't breakdown water molecules or decrease absorption of water (cont'd)
    – fixer1234
    Jan 6, 2023 at 17:43
  • vapor to reduce staling. Internally trapped CO2 needs time to be displaced by liquid water at the start of brewing, the purpose of the blooming stage. A dessicant (air drier) will absorb and hold free moisture so it isn't available to be absorbed by the coffee, but most forms that would be suitable for use with coffee don't aggressively attract water in a way that would adequately dry out moist coffee. But if you could find the right one, use a lot of it in relation to the coffee and a lot of mixing, and then separate the coffee for use, you might have hit on a solution.
    – fixer1234
    Jan 6, 2023 at 17:43

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