After my experience today, I am rethinking how much difference grind coarseness makes on coffee. I brewed my first Aeropress today - two brews back to back and I drank the coffees at same time comparing the tastes. This was my first time to compare different brews. I was surprised that materially different grind sizes but all else equal, did not make materially different coffees.

Both brews the Hoffmann Aeropress method. ~11.5g of coffee at 18.18:1 for both brews. 209F water. First brew grind was a Ditting Sweet 4.0. Second was a 6.0 grind.

Both coffee were very close in taste. Both were a winey, tangy, blood orange citrus taste. The 4 was a little richer. The 6 was a little brighter but again, fairly similar coffees. The 4 ended with an oatmeal cookie like taste at very end after cooling. The 6 ended with a lighter, almond cookie like taste. The 6 might have been a sharper sweetness (not sugar but closer to sugar than the 4 which was more honey), but both were overall sweet.

I would think a grind with a ~50% larger diameter would taste more different but they were fairly similar coffees.

Perhaps this is because Aeropress is an immersion brew? With immersion brews, the solvent (water) tends towards equilibrium so it's probably not very sensitive to grind size. As the coffee is in long contact with the water, it's largely going to pull out what it can until equilibrium. This is for relatively similar grind sizes, but if you go way coarse then there may be interior bits that don't touch water.

Compare against percolation / pour over, where fresh solvent is being introduced throughout the brew, and dissolution rates apply. Here grind size makes a larger difference, because different grind sizes allow access to solute at different rates.

Roger, this is about the same as I experience. I can chuck almost any grind, from fine to coarse, into my Aeropress, and the coffee comes out more or less the same every time. About the only change I make is to let it steep longer for the coarser grinds. It's the most forgiving coffee maker I own (and I have a bunch of different ones). I've never really thought about why this is so before, but Mike's explanation seems plausible to me. Thanks to you both for making me think about this.

to add to @mikelipino comments and since it seems you're already tuned into Hoffmann, JH compares percolation and immersion in this video and is able to show that immersion at the very least is the safest brewing method and is hard to mess up regardless of grind size where percolation is far less forgiving. He even concludes by talking about the Aeropress and then teases an upcoming Aeropress video which I presumed you watched since you're using his recipe. For this reason, I use my Aeropress when I travel all the time because I don't need to worry about timers and scales and I still get very repeatable results.

I would assume the long brew time and hot water would tend to give similar results. I've had my aeropress since 2007 and after many espresso machines it is now my daily driver exclusively. Over the years I have tried a very wide variety of recipes. I have finally settled on nearly exactly Alan's recipe described in the youtube video : "Alan Adler AeroPress Lecture at CoffeeCon San Francisco 2014" . So: fine grind, cooler water, short contact time with less water, and topped up afterwards in the cup with (hotter) water. My guess is that you would get more variations using a similar method. I am happy using 12g in, and filling to #2, quick north-south stir and plunge, then add water to get the final strength I like.
regards, Rich

Jeff Verellen won the World AeroPress Championship in 2011 and 2013 and is known for using a cooler brewer temp. (you can get his method on the WAC winners page). It's not so different than Alder's original

Here's his reciepe
1. Bloom 40 sec with 50ml water
2. Add 220g water (total 270) at 79°C
3. Press slowly for 30 seconds
4. Leave approx. 50g in the brewer (both water and coffee)

I applaud Verellen's version for doing something different than anyone else at the time which is what competitions are about but what's funny is it's essentially the recipe that comes in the box.

https://www.nature.com/articles/s41598-021-85787-1.pdf
https://static-content.springer.com/esm ... M1_ESM.pdf

Can you get that high of extractions with Aeropress? Doing such a fine grind, off boil water and 18.18:1 ratio, I assume my first brew would have been near the top for Aeropress.

You could certainly get to 24% extraction in an Aeropress. I've achieved 24.9% on one occasion. It was a dark roasted coffee. With a medium roast and the same brew method I got to only 23.4%. That brew method was using a fine grind but 80°C water, a 10sec steep, and a slow plunge. With a longer steep the extractions would probably have been higher. In that journal article they were mainly interested in equilibrium extractions which took at least 20 minutes to achieve. Most people don't brew that long, both because they don't want to wait and also because at some point extraction can carry one into a less tasty region, depending. More typically I've measured my Aeropress brews at around 20%.

The point was simply to illustrate that grind size does have a measurable effect on extraction. And with more typical 2-6 minute brew times the difference might be exacerbated as it could affect the rate of extraction. But to what extent one can taste those differences is harder to say.

Note the scale on the supplemental figures from the Nature paper. Per the Nature paper cited above, p. 9, paragraph 1 (emphasis mine):

"The coffee grind particle size did have a very minor effect on TDS. For the brews at Rbrew = 15 at 99 °C, both the equilibrium TDS and E are negatively correlated with the median of grind particle size with a correlation coefficient of −0.978 and −0.992 (solid lines in Supplementary Fig. S4), that is, coffee brewed with finer coffee grounds resulted in slightly higher TDS and E. The TDS was 1.36 ± 0.09% over a huge range of grind particle sizes, from a median particle size of 579 μm to 1311 μm (cf. Supplementary Fig. S1), but these small TDS differences are difficult to discern compared to the major effect of Rbrew over the entire range of brew ratios tested.

TLDR, grind size has a minor effect on TDS, but it's largely overshadowed by brew ratio.