A couple of things that may be of use (and may not):

1. Look into the AeroPress Timer app, and work your way through the recipes. I did so every time I got a new grinder, so I'd know what settings to use for that grinder in particular. So in general, I experimented with only one variable - the grind - until I found the right setting. By the third time through the list of recipes, I was starting to change other variables in order to tweak each recipe to my tastes. And .... it allowed me to get to know the brewer in a way that helped me understand it. The recipes also vary things like stirring/breaking the crust, steep times, the speed of the pour (which also causes agitation, and can break the crust), stuff like that.

2. I don't like inverted recipes. I find them a little messy, and kind of a hassle. On the other hand, I DO like the effect they sometimes get, and how they don't allow the coffee to seep through until you are ready for it to go through. SO. I use the Fellow Prismo attachment, and brew all recipes non-inverted. I also use filter papers, just sitting on top of the metal filter that comes with the Prismo. It has the advantages of inverted brewing, without the disadvantages.

My 13 year old A-P has been my daily driver for all of 2021, usually 3x/day. I think water temp is very important and I believe Alan's advice of 85C/185F is the best for me with city to city+ Ethiopians , having tried hotter water many times. I have a standard method I like that takes 1.5 minutes. After 10 different espresso machines, only my very first one is left but no longer used. Life is so much easier without that hassle and I can sip on a coffee often until the last is room temp instead of gone in 30 seconds.

lukehk wrote:I use Michael Fabian's method with a 4 minute steep. Produces results similar to a cupping but this recent blog from Jonathan Gagne looks interesting https://coffeeadastra.com/2021/09/07/re ... aeropress/

Mr. Gagne said:
"One trick that allowed me to get the most consistent brews was to absolutely avoid stirring in circular motions. Doing so will cause the coffee particles to deposit into a dome-like shape, and this bed shape will cause most of the flow to happen on the edges of the coffee bed when the plunger is pushed in. "
This reminds me of "tea leaf paradox".

5cylinders wrote:Recently I have settled on using Aeropress in hybrid method. Instead of inserting plunger right after pouring to stop the dripping , I do it at 1:00, press at 2:30 (sometimes at 3:00). The cup is not bad to me.
The problem is : Aeropress forms a very deep crust. I'm not sure how it affect extraction and what I can to with it. I take some tests, stiring immediately after pouring, at 1:00 right before inserting plunger, right before pressing, 30 seconds before pressing, or simply ignore it. The results are inconsistent, now I'm comfused even more.
Any help would be greatly appreciated.
Thanks.

ground coffee will float from trapped CO2 which is how the crust is formed. because the Aeropress is a narrow column the crust will be deeper. Like any crust agitation will cause it to sink referred to as breaking the crust'and it effectively stops the brew in immersion unless the sunk bed is agitated again. Blooming the coffee will prevent the crust from developing so if you don't like the crust you might want to try that. blooming/crust development sits at opposite ends and I find them to be is quite misunderstood in the coffee world. people tend to be more check box driven but don't really know why what's going on.

historically terms like the crust or breaking the crust have been used for cupping which is a very basic way of immersion coffee to grade coffee and we can see the same thing happening in a french press. when you let a crust develop in percolation (no bloom) you get that rising cake look in the coffee bed that Asian markets seem to covet. But it's not magic it's just coffee floating on top of the water no different than immersion brewing the difference is water is always escaping and replaced with fresh water. contrary to trending pour-over methods it's a legitimate method where you do an initial wetting the ground in a swirling motion then once all the coffee is wet you switch to a center pour with no pause for a bloom. the center pour will put the water under the crust and cause a look of the crust rising like a cake, even in multi-pour methods if you keep to a center pour the crust never really gets fully broken and will continue to float. once the crust is developed agitation to that crust will cause it to sink so a switch from a centre pour to a circular can break the crust. Typically with these methods, the final result will be a concaved look of the coffee bed as the water escapes and leaves the coffee along the walls of the brewer. With a continuous crust, extraction is from diffusion from the concentration gradient closer to the crust and less about water percolating through a sunk bed, the brew is also quicker. There are so many varied versions of these creating very inconsistent results which is why the west has abandoned these eastern methods but often the brew is more tea-like, and this may be why it is is a more desired method in Asian cultures.

when you bloom coffee it releases trapped C02 causing the coffee to be saturated with water and heavier so it sinks. Coffee with depleted CO2 will develop less of a crust and coffee will sink a lot easier even without a bloom. so depending on the amount of trapped CO2 (or how fresh your coffee is) you may need to bloom longer or agitate more aggressively and the inverse is true, depleted CO2 (or old coffee) means you don't need to bloom aggressively or at all. blooming is desired for percolation as it puts the coffee where you want it, at the bottom, to allow water to pass through which is the definition of percolation.

With hybrid brewers or steep and release type systems whatever your method you want to end off with the coffee resting at the bottom of the brewer for that "release" part to be percolation. with the AP it is forced out with pressure but it's still percolation and for the most consistent results you will want the coffee bed sitting at the bottom. so with the AP I would either bloom or break the crust but don't "stir" the coffee. breaking the crust is just agitating it sufficiently so the coffee sinks and you don't want any swirling or circular motions. back and forth are probably better but you don't want this to be too aggressive. you may go deep or shallow but do it consistently and the same each time.

Thank you for the detailed explanation. Very helpful, and practical.
I blame myself for being paranoid about the curst. For me it used to be like a sullen butler in a thriller who is not even a murderer, or a cloud of which the only job is to make a meteorologist sullen.
Now I can move on, under the guidance of everyone here.

I know that James Hoffman says it is an unecessary complication but I like the upsidedown way of Aeropressing- if nothing else it seems much more convenient to me.

- I put the plunger in- same every time, dump in my grounds, shake to level, add 25g or so of water, strir than in very gently then take 20-30 seconds to fill the cylinder ( works out to just about 200g)

I have the cap with filter sitting on top of the cup - a drop of water to wet the filter (so it sticks when I flip it over later and does not drop out) and then cover the cylinder with that just sitting on top.

At 1 minute after the pour is done I lift the cap off and give one gentle down-and back swish to dissipate the crust, and screw on the cap properly.

At 2 minutes in, I flip the whole thing over onto the cup and rest my arm on the top - it slowly - 30 seconds or so, goes down. The whole process is about 3 minutes of steeping time. Good every time, though in fact, I recently reduced the coffee dose by quite a bit and have much better coffee as a result - somehow I'd got into a groove of putting 17 or 18 grams in there for the 200 g of water; 12-13 is way better.

Andrew,

Your post has honestly made my day ....I have heard people talk about all these but your detailed post has shed some light on the how and the why. Beautiful man....this is a testament to the coffee knowledge you have. Just curious on your brewing style ....so do you use agitation in only percolation and not in immersion ? . My recent cups with large Vietnamese phin rivals any kalita or melitta and is a bench mark definition in filter coffee , where the grounds are held at the bottom by the spreader and all water mass dripping through it. Too much agitation especially in a immersion setup does no good.

I have also heard that breaking the crust in full immersion causes the grounds to " fall out of suspension " and drastically reduce extraction. But why does it reduce extraction. Wonder what the science behind that is . Just because it falls to the bottom why would that impede with extraction. So if this indeed true , will all old coffees (with no crust formation ) fair poorly in a immersion setup. Wish I knew the answer.

in immersion, a crust develops and is not really suspended within the water but on top of the water. coffee will naturally sink to the bottom as it absorbs water and this is a similar effect to blooming coffee as the act of blooming will cause the coffee to absorb water which will keep it at the bottom. old coffee will still float it will just sink more easier. in immersion, extraction happens through diffusion, and when the coffee sinks the extration effectively stops and you would have to agitate if you wanted to extract more. with diffusion there is an area of high concentration (the crust) and there is water movment through the high concentration to low concentrations I think mostly by convection. once the crust is broken the area of high concentration disperses. When the coffee sinks and forms a bed it becomes the new area of high concentraion but diffision doesn't happen because there is no agitation and water is not really passing through this sunk bed. this type of extraction is like a tea bag. if you drop a tea bag in hot water not a whole lot happens, the tea bag is an area of high concentration and the surrounding water is an area of low concentration but when you shake the tea bag (agitate) the low concentration area gets a burst of tea stuff but if you never shake the tea bag you get some pathetic tea.

cupping is done with immersion and once the crust is broken and the surface is skimed the coffee sits there until it's cool enough to cup (slurping it from spoons, not drinking it). this wait is about 5 min. multible passed are made cupping the coffee as it cools and it can go for quite a long time until the coffee even reaches room temperature. All this time the coffee sits at the bottom and if left undisturbed it doesn't make the coffee stronger or increases the extraction. so it may seem odd but in immersion a sunk bed of coffee doesn't do anything to the extraction as long as you don't disturb it. this is exactly what I do with immersion brewing like a french press, after I break the crust I don't press I let it sit so it cools and all the floating bits sink, then when ready I leave the press fully exenteded because if you press it then it will distrub the coffee and I decante it out. The cups are actually much cleaner than immediately pressing and pouring out the coffee.

DamianWarS wrote: When the coffee sinks and forms a bed it becomes the new area of high concentraion but diffision doesn't happen because there is no agitation and water is not really passing through this sunk bed. .

Rate of Diffusion in immersion method is directly proportional to the concentration gradient . Bigger the difference in gradient , higher the diffusion and I agree. That's the main reason percolation is way better in extraction.
But you state that when coffee sinks to the bottom , it becomes the new area of high concentration. So what exactly stops the diffusion process.
Just because grounds switched places from top of the brew chamber to the bottom, why does it stop diffusion process. Is this because the concentration gradient got reduced perhaps ?.

I don't know why diffusion stops and I suspect it's something to do with convection or a lower concentration like you mentioned the rate of diffusion is proportional but whatever happens, it does stop, at least on practicle applications. I do know TDS readings are higher closest to the slurry than at the top of the brew so there still is a concentration gradient but I'm sure it is not as great as what it formally was. diffusion is likely still happening but at such a slow rate it doesn't do much and if never disturbed it really doesn't impact the brew so long as you're not leaving it for like an hour. cupping uses immersion and no filters and a cupping session after the crust is broken could be 20 min easily so if diffusion is happening it's too slow to matter. So I may have misspoke and there isn't much value in calling it a higher concentration in practice but the broader point is that it's no longer extracting.