Here's a quick rundown of the Aeropress method I use every morning. I end up with a relatively crema-y shot. You'd never mistake it for one from an espresso machine, but there's a good layer all across the top.
This is completely unscientific and I can't identify which steps here are the relevant ones for the good results, but maybe if you experiment with some of these adjustments you can identify what works and what doesn't.
The beans I use vary; I generally grab a light or medium roast off the shelves at Trader Joes and grind it one click down from the finest setting on the in-store grinder. (The finest setting purports to be for Turkish coffee; the one I use is labeled 'espresso'.)
I store the ground coffee in its can in the fridge for up to a week or a week and a half, depending on how long it takes me to drink it all. Today I'm using Trader Joe's Jamaica Blue Mountain Coffee, a delightful medium roast. (I just now learned that Serious Eats says it's the best bet for Trader Joe's coffee.)
Melted snow from the Wasatch Mountains, filtered through whatever the county of Salt Lake does before it gets to my kitchen tap, and heated on the stove until just before the boil. There are tiny bubbles forming on the bottom of the kettle, but few of them are rising to the surface of the water.
I'm pretty loosey-goosey about my brewing method, but the results are very consistent. This leads me to believe it's the equipment and the beans that are generating the great results, not anything I'm doing right.
- Set up the Aeropress for inverted brewing.
- For one shot, use a generous scoop of ground coffee. Tap the assembly on the counter so the mound of coffee flattens out.
- Slowly add your just-off-the-boil water. (I use a gooseneck kettle for easy, controlled pouring.) Rotate the Aeropress as you pour and do so until you can no longer see any dry grounds. (The chamber should be about 2/3 full when this is complete.)
- Stir slowly until you get that lovely uniform light brown color on the top of the mixture. I use the handle of the scoop for stirring.
- Place the cap and filter on top of the assembly and wait 15-60 seconds. (My own brewing time varies wildly, depending on what distracts me during that time.)
- Press. With this fine grind and filter, you'll have to press a little harder than with the coarser grind. As you press you'll see foamy buildup gather on top of the grounds. You'll have to press extra hard at the end to squeeze all of that through, but it will drip down onto your shot at the end and form that delightful crema.
As I pay more attention each morning, I've noticed a couple more things:
- My results vary significantly. I think the contributing factors are the grind and how hard I press at the end.
- I never use soap on my Aeropress equipment. I rinse it with tap water after each use, but never run it through the dishwasher. There may be buildup of coffee oils on the surfaces that helps (or hinders??) the foam making process.
For the past few weeks I've been casually experimenting with my morning coffee and coming up with very inconclusive results. (As I mentioned below, all I've come up with are a bunch of totally surefire ways to absolutely demolish the crema, and no methods of preserving it.)
This half-butted casual science ends now! I just bought a hand grinder and an app full of AeroPress recipes; thusly armed, I'm going to experiment more formally. Well, a little more formally. I'll track the results here and update this answer when and if I come up with a reliable way to generate and preserve the foam on my AeroPress shots.
Edit The Third:
The results are in: I've figured out how to stop killing my crema. It turns out that the combination of freshly ground beans and the mesh metal filter is somehow stopping the crema from getting through to the cup. Eight attempts with hand-ground beans failed miserably, and my first attempt after reverting to store-ground beans (with the 'somewhat loosey-goosey' method above) generated a nice layer of foam in the cup.
However, the plot thickens. My colleague Robert asserts:
Never had a problem getting crema with aeropress. Lots of fresh coffee ground to a powder, very little very hot water. Makes my ubercoffee syrup shots I talked about a year or more ago... with plenty o crema. Dilute to taste (which I never did < jitter >).
...and I'm not entirely sure, but if memory serves, switching to the fine metal mesh filter meant bye-bye to crema. It's been a bit too long to remember for certain. I just reused the same paper filter over and over for months (actually, I used two to keep them from blowing out).
So it would seem that:
- Freshly, very finely ground coffee + paper filter + not much water = crema city
- Coffee ground fine in the store + metal filter + water = crema town
I'd be interested to see others' results from experiments like these.