Freezing and Microwaving Coffee Beans


Hi everyone!

I usually keep my coffee beans frozen for long term storage. Normally I bring them up to room temperature before using them, but it got me wondering, how would the temperature of the beans affect the brew? I did some experiments to find out.

As I wrote in this post about storing coffee beans, I recommended to avoid using the beans right out of the freezer. The reason being when frozen beans contact the warmer air, it will cause condensation of the moisture around leaving the beans slightly wet. As you can imagine getting your beans wet before you want to use them is not a good thing. So the point was to keep the beans left in your frozen bag dry, not about the temperature of the beans.

As a side experiment, I thought if I’m going to test for the impact of temperature I should also test for hot beans as well. So I will be microwaving some beans to see if that has any impact. I cannot imagine how anyone would end up with hot beans but hey, it could be interesting.

The experiment

I will compare 3 samples. One that was in the freezer for half a day, another that was microwaved, and one at room temperature for control.

Of course I used the same beans from the same bag for the 3 samples (I used the ROKUMEI BLEND, which I reviewed in Japanese). I will use the same ratio of 9g of coffee to 150g water. To eliminate the factor of technique as much as possible, I used the HARIO SWITCH immersion brewer.

In order to minimize the effect of different storage conditions, I did not freeze the beans for so long. I put 9g of beans in to a ziplock bag and put them in the freezer for about 4 hours, which should be enough to lower the temperature.

For the microwaved beans, I microwaved 9g of beans for 1min at 600W. They were very hot. I could not touch them without getting burned.

Grinding the beans

Now that I have the samples, the first thing to do is to grind them. I used the TIMEMORE SLIM PLUS grinder at the same grind setting.

Visually they didn’t seem to have a noticeable difference.

The beans I used were quite a light roast, so they usually provide quite a bit of resistance when grinding. But I did feel that the frozen sample seemed to be a little bit lighter. On the other hand, the hot beans seemed to grind a bit smoother with fewer hick-ups.

But to be honest the difference was very small.

Taste Test

I only have one HARIO SWITCH dripper, so the brews need to be prepared in order. This means that the cup prepared first will be significantly colder than the last cup prepared.

To minimize this difference, I taste tested the 3 cups after they were sufficiently cooled down.

An pretty much as expected, there wasn’t a very significant difference between the three.

To me, it did feel like the frozen one had a bit more edginess to it than the others. It gave me the impression that the beans were slightly over extracted, as though it was ground slightly finer. It might be that frozen beans lead to more fines being produced.

The coffee beans I used are a pretty lightly roasted bright blend with a clean acidity. The acidity does not linger making it very well balanced, but with the frozen sample the acidity did seem to stay a bit longer then I would like.

On the other hand the microwaved beans really did not show any differences compared to the room temp sample. This was a bit of a surprise in the sense that I expected microwaving beans would degrade them. I was half expecting a very bad cup, but it was very normal. It turns out that 1min at 600W will not do too much harm to the beans.

So to conclude, as far as I can tell the temperature of beans do not make a very large impact on the brew. But I would still try avoid brewing with frozen beans.

You definitely do not need to microwave your beans. But since it did not seem like microwaving beans do not affect them, I could imagine microwaving frozen beans to bring them back to room temperature in a pinch.

Let me know if you have ever tried something similar. Did you find anything different?