I've been brewing my coffee with an AeroPress for a couple of years now and I've become aware of the huge number of variables available to me in making my morning Java. Assuming the same bean and roast level, I see

  1. amount of ground coffee,
  2. grind coarsness,
  3. temperature of the water,
  4. steep time, and
  5. using the AeroPress right side up or upside down,

as the variables I can play with to vary the taste. Some of these variables may offset each other as well. For example would steeping coarser ground coffee result in the same taste as less time steeping a finer grind? Or how about coarser ground coffee in hotter water v. finer ground at lower temperature?

I'm searching for the key variables in my control to play with to maximize the effect on taste.

  • Would you have any update on this thread? More than a definitive answer (that would help though), I am interested about your findings. Feb 3, 2016 at 0:20
  • 2
    @EricPlaton I have found that the hotter the water along with too fine a grind, the more bitter the brew tends to be. Too cool and there is insufficient extraction so the brew seems weak and watery. Steep time doesn't seem to make that big a difference I suspect because the water has cooled off. The other factors varied within reason do have some effect but it's minor. One thing I didn't list and should have is the freshness of the roasted beans. Since that post I've started roasting my own beans and after a bit of a learning curve, have never had better coffee.
    – PJNoes
    Feb 3, 2016 at 23:19
  • That is too interesting a comment to leave it as a comment. How about you post it as an answer, and perhaps mark it as the answer (or Evan's one?) ? Feb 4, 2016 at 0:16

2 Answers 2


A few other factors to consider:

  • Freshly ground beans.

  • How you store your coffee beans. You basically want to keep them reasonably cool and away from oxygen, sunlight, moisture and variations in temperature (which is why you don't keep them in the freezer except for long term storage). Generally in the pantry in an opaque, air-tight container. I one-way valve is recommended as recently roasted beans will emit CO2. I bought a stack of 250g resealable foil bags with the one-way valve from a local roaster and would use each bag a few times. These days I use AirScape canisters.

  • The water you use. If you wouldn't enjoy drinking your tap water, don't use it to brew coffee. Use the same water you use for drinking water.

  • The amount of water you put in the Aeropress vs. the amount of water and/or milk you add afterwards (if any).

  • How vigorously you stir with the paddle. Generally you want to stir just enough to ensure all the grounds are thoroughly wetted, and that there are no air pockets. Stirring too much can over-extract which will increase the bitterness.

  • When pressing into the cup, do you only press until you hear the air hissing through, or do you keep going and compress the puck, squeezing out every bit of water you can?[1] The latter can over-extract and increase bitterness.

  • Using paper filters vs. a metal disc filter. Also, some people believe pre-rinsing a paper filter makes a difference.

Obviously there are a lot of variables, and people can become amazingly pedantic. Fun if you don't mind a bit of experimentation.

With regards to water temperature, the general wisdom is that you want the slurry of coffee and water to brew at around 95°C, which is just a bit under boiling for optimal extraction. This video gives some pretty good advice on this. Pre-heating the Aeropress would probably make the biggest difference here[2]. I usually just wait until the water in the kettle stops bubbling before pouring. Apparently it is possible to burn the grounds if you hit them with water that is boiling.

The other bugbear I have is with retention in coffee grinders. Retention is when grounds are left up in the works of the grinder, and often the grounds can come out very staticy and cling to everything and make a mess. This grosses me out as it means old grounds from previous grinding will be dropped in with the fresh grind. Weighing the beans before and after can show a variation of half a gram or more. Urk.[3] However I've found that sprinkling a couple of drops of water on the beans before grinding almost completely eliminates retention for me.[4]

[1] There's a term for over-squeezing the grounds that escapes me at the moment.

[2] Having lived a lot of my life in drought areas, using and then discarding the water to pre-heat my Aeropress or French press is something I find surprisingly hard to do.

[3] I did mention people can become amazingly pedantic, didn't I?

[4] Known as the Ross Droplet Technique

  • 1
    Thanks, that's very comprehensive. FWIW, I control most of the variables you've listed very well, although I do use the paper filters. I'm really asking about variables that aren't as obvious determiners of taste as well as variables that might offset each other. For example, temperature of the water vs time steeping, OR, grind coarsness vs temperature, OR, time steeping vs. coarseness, etc.
    – PJNoes
    Mar 9, 2015 at 19:17
  • 2
    A good objective answer for a reasonably subjective question.
    – James
    Mar 17, 2015 at 13:06

Assuming the same beans and roast level, I think the variables that affect the taste most are the freshness at all stages. All other variables make the difference between great and merely good, but they may not affect taste in ways as noticeable as freshness.

Freshness at all stages means the roast freshness and the ground freshness, as well as the fruit itself.

A tricky aspect of this answer is that "fresh" does not necessarily mean the "shortest life". For example, I like working with green beans that came just a few months ago at most, after they get stable in their new climate. After roasting, the best taste comes up 2-3 days later in our case. And brewing comes right after grinding---always. This example is for illustration purpose; numbers may not serve elsewhere. The point is really freshness along the bean lifetime, and the fuzziness of freshness.

This answer lacks references. I will try to back all that up.

  • 1
    I agree with freshness being proably the most important. To that end I've ordered a small roaster, but haven't got it yet. I'll be very interested to see how my coffee improves since I don't really know how old the beans are that I'm currently buying. I know this is important because not long ago my wife brought me home some roasted beans that had a expiration date 9 months away. The coffee tasted like cardboard - horrible! So I do have an appreciation for freshness :-)
    – PJNoes
    Mar 9, 2015 at 19:20

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