Most Aeropress arguments are not about technique. They are about which of two drinks the people arguing are making, and neither side says so out loud. One camp brews at roughly the ratio of a pour-over and drinks what comes out of the chamber. The other brews at close to twice that strength, presses a small volume, and adds hot water in the cup. Both are following someone credible. They are not making the same drink, and most of the disagreement disappears once that is on the table.
The ratio selects the drink. Around 60 grams of coffee per litre of water gives you a filter-style cup you drink as it comes. Around 100 grams per litre gives you a concentrate that expects to be diluted afterwards. Neither one is espresso. Anette Moldvaer's baseline is 12 g to 200 ml, steeped 30 to 60 seconds, which works out at 60 g per litre and sits in the same place as the single ratio that covers every filter brewer in the house. James Hoffmann lists roughly 100 g per litre for a short strong Aeropress. That is a concentrate by design, and it is built to meet water later.
What dilution changes, and what it leaves exactly as it was
Adding hot water to the cup moves one number. It lowers the concentration of dissolved coffee in the liquid. It does not touch how much you pulled out of the grounds in the first place, because that transaction finished when you pressed. Those are two separate measurements and confusing them is the most common reason people cannot fix their coffee. If that distinction is new, strength and extraction are not the same thing and the difference is where most bad coffee comes from.
The reason dilution feels so much like a fix is that concentration is a volume knob on the two faults you are most likely to be tasting. Jessica Easto, writing on coffee sensory work in How to Taste Coffee, notes that perceived bitterness has been linked to total dissolved solids, so the same coffee at higher strength reads as more intensely bitter. The same work she cites found the highest perceived sourness in brews that were high in dissolved solids and low in extraction, and the flattest, least acidic-tasting cups in brews that were low in solids and high in extraction. Concentration turns both faults up and down together.
So a harsh concentrate becomes a pleasant cup with 100 ml of water, and it is tempting to conclude that the recipe worked. Sometimes it did. If the concentrate is genuinely well extracted and simply too strong to drink neat, water is the correct answer and the cup is good. But if the concentrate is sour because the grind was too coarse or the steep too short, dilution gives you a weaker sour drink, and you will spend a month adding more water to a problem that lives in the grinder. The diagnostic to run first is whether the fault is sourness or bitterness, because they point in opposite directions.
There is a cost to the dilution route that nobody advertises. Strength tracks with body. A strong brew reads thicker in the mouth and a weak one reads thinner, and bypass water thins the texture along with the intensity. The concentrate method buys you precision over the final strength and pays for it in mouthfeel. A cup brewed at 60 g per litre start to finish arrives with its body intact because no water was added after the coffee left the grounds. Whether that trade is worth making is a preference, and it is a real one, not a rounding error.
Why the concentrate route exists at all
It is not showmanship. The Aeropress chamber is small, and a full mug at filter strength does not fit in one pass alongside the grounds. Brewing 16 g in about 130 ml and topping the cup up to 250 ml gets you a mug-sized drink from one press, at whatever final strength you decide, without brewing twice. That is a genuine mechanical constraint producing a genuine method, and it is the honest reason the two ratios both exist.
Temperature is where the Aeropress literature gets loudest and least reliable. Alan Adler's own instructions for the device specify water at roughly 175°F, well below the 195°F to 205°F range the Specialty Coffee Association uses for brewing. Both positions are defensible. Lower water with a longer steep and a fine grind can land in the same extraction window as hotter water with a shorter one, and Adler was solving for a drink he liked. What is not defensible is the reasoning that travels with it. The Aeropress recipe literature justifies the low temperature by asserting that hotter water damages nutrients in the coffee. We went looking for a peer-reviewed or official-body source for that and did not find one, and the books repeating it do not cite one either. Until somebody produces the measurement, 175°F is a taste preference, and a taste preference is a perfectly good reason to brew that way.
The espresso claim, which is the one worth killing
Press hard on a concentrate and something foamy appears on top of the cup, and a whole genre of recipe writing calls the result espresso. Espresso is defined by about nine bar of pressure, a ratio near 1:2 by weight, and 25 to 30 seconds of flow. A hand plunger generates a fraction of one bar. The foam is chamber air forced through the coffee bed, and it collapses within seconds, which is the tell. Real crema is an emulsion of oils and carbon dioxide held together by pressure, and the foam on top of your cup is not the quality signal it is sold as.
The related claim, repeated across the Aeropress recipe books, is that this method produces less acidic coffee than drip or a press. Nobody has published a measurement of Aeropress pH against a V60 of the same beans that we could locate, so the claim has never been tested against the thing it is compared to. What has been measured points away from it. Rao and Fuller, in Scientific Reports in 2018, brewed light roasts from Brazil, Ethiopia, Colombia, Myanmar and Mexico both hot and cold and measured the finished liquid. Hot brew came in between pH 4.85 and 5.10, and cold brew of the same beans landed in a comparable band, the two methods together spanning 4.85 to 5.13. That is a laboratory measurement of brews and not a study of people, and it supports one narrow point: dropping the brew water from near boiling to room temperature, a far larger change than swapping one brewer for another, barely moved the measured acidity. What the method does move is perceived sourness, which is a sensory response and not the same quantity. The acid load has not been shown to follow.
What the Aeropress will not do
It will not make espresso, and so it will not make a base that layers properly under steamed milk. A cappuccino holds its shape because espresso is dense enough to sit under foam. Aeropress concentrate mixed with milk makes a decent milky coffee and no amount of technique converts it into a flat white.
It will not repair a bad grind. The fine paper filter catches fines on the way out, which is often sold as making grind size irrelevant, and it is not true. Dust over-extracts and boulders barely extract, and both of those happen inside the chamber before the filter sees anything. The filter cleans up the cup. It cannot un-mix two different extractions that already happened inside it.
It will not make coffee for four people. It will not do what the low-acid marketing around it implies, because the comparison it rests on has never been measured, and stomach comfort is not something anyone can predict from a brewing device in any case. If coffee reliably upsets you, that is a conversation with a doctor and not a change of dripper. And it will not look like much on a counter, because it is a plastic cylinder, and it was designed by an engineer who cared about the drink rather than the object. Everything attractive about an Aeropress station is the things around it.
How you know which drink you are making
Weigh the coffee and weigh the water, including any water you add to the cup afterwards. Then divide. If the total lands near 60 g per litre you made a filter cup, whether you diluted or not, and it should taste like one. If it lands near 100 g per litre in the cup, you made something closer to a small strong coffee and it should taste denser and shorter.
Run both in the same session on the same beans. Brew the 60 g per litre cup, then brew a concentrate and dilute it to the same final strength, and drink them side by side while both are warm. If they taste identical you have learned something useful about your palate. Most people find the diluted one thinner and cleaner and the direct one rounder, and once you know which you prefer you stop reading recipes. Comparison is the whole method here, because a single cup on its own teaches you almost nothing.
One practical note about the press itself. The device needs something under it that will not slide or tip when you lean on it, and a light cup on a wet counter does exactly that. A heavy stoneware mug with a wide base solves it, and so does pressing into a squat glass server and pouring across. Neither needs to be expensive and neither needs to come from us. For this job any wide-mouthed vessel with enough mass to stay put under load will do.
The Aeropress costs about $40 as of August 2026 and it will outlive most of what sits next to it. What it will not do is choose your drink for you. The ratio does that, and until you decide which of the two you are making, you are troubleshooting a recipe that was never broken.