The inventor of the Aeropress, Alan Adler, recommends a slow press on the Aeropress. He uses his forearm to push down on the Aeropress. This imposes somewhat of a limit on the pressure you can exert because if you push down too hard your arm will quickly get uncomfortable.
For months, I had been using quite a fine grind on the Aeropress. I was making a lot of tasty brews and I was able to detect the flavours in the coffees well. Bitterness was not overwhelming. But my brews were somewhat inconsistent. Some brews were cloudier than others. I had come to accept that a cloudy brew is part of the Aeropress experience.
In a recent post for the Steampunk Coffee blog, I wrote:
"I suspect this is because pushing too hard can cause blockages in the Aeropress filter. But, I am yet to research this topic in more depth."
A recent white paper by Nasko Panov of NP's Coffee Science blog conducted a number of experiments to verify what causes the cloudiness—also called "turbidity"—of an Aeropress brew. He used a spectrophotometer to conduct the experiments, a tool I do not have (nor knew existed until reading Nasko's paper).
This paper proved that pushing slower does indeed make a clearer brew, proving what I had suspected about the slow press. I have been having such a good experience with a slow press that I've come to associate coarser grinds with better brews on the Aeropress. There is a fine line between deliciousness and a somewhat flat brew but a grind closer to what I'd use for pour-over seems to be a good balance. This is around the 20 mark on my Baratza Encore (with room for experimentation).
My reasoning, however, was not sound. I thought that pushing too hard would cause blockages in the filter. This paper suggests the degree to which the Aeropress cap is screwed on impacts the cloudiness of the final brew. The harder the cap is screwed on, the less turbid the brew would be. This is because pushing hard opens up gaps between the filter and the plastic cap, thus allowing more grounds to fall through.
This evidence further affirms my conviction that a lighter push is better. I should remind you that you can achieve a lighter push through a coarser grind. I was always using a fine grind and this was what was causing problems. My brews were visibly cloudy. I only realised coffee did not need to be as cloudy when I brewed with the Kalita Wave, a device capable of making a much "clearer" brew.
When I look back to photos of my first brews, I did not notice this cloudiness. I think this was because I was using preground coffee which was a bit better in terms of pressing. My first brew was very coarsely ground. I started to use a finer grind as soon as I got my own grinder. I only really started to notice the cloudiness in my brews toward the end of the year.
This is a welcome discovery because cloudy brews, for me, are not as tasty as clearer ones. I am definitely going to stick with a coarser grind and push more slowly using the plunger.
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