AeroPress Guide: How the Press Works and How to Brew a Better Cup

The AeroPress is a small plastic coffee maker that works like a giant syringe. Ground coffee steeps in hot water inside a tube, and then a plunger pushes the coffee out through a paper filter and into the mug below. AeroPress says the Clear brews and cleans up in about 2 minutes. The brewer controls every variable: how fine the coffee is ground, how hot the water is, how long it steeps and how hard it is pressed. Below are how the press works, the maker's recipe, the upside-down "inverted" method, what the filters change, and what a mile of altitude does to the water (shop coffee and tea tools).

Where the AeroPress came from

The AeroPress was invented by Alan Adler, an engineer who, according to the company's own history, has been honing his inventing skills since he was 13, taught a sensors course for mechanical engineering students at Stanford University and invented the Aerobie flying ring, which set a Guinness World Record for the farthest thrown object. Adler was unhappy with the coffee he got from home coffee makers. He spent months studying which variables in brewing change the taste, then designed a manual press to brew under the conditions he settled on. The company says the work began in his garage in Palo Alto, California, took two years and more than 30 prototypes, and ended with the AeroPress being introduced at Coffee Fest Seattle in November 2005. In the company's words, Adler used air pressure to shorten the brew time and reduce bitterness.

How the press makes coffee

Brewing coffee is a process called extraction: hot water dissolves flavor compounds, acids, oils and caffeine out of the ground beans. Brewers get there in two broad ways. In percolation, water passes through a bed of coffee once and drips out, as in a drip machine or a pour-over cone. In immersion, the grounds sit in the water for a set time, as in a French press. The AeroPress uses immersion first and then something neither of those methods has: pressure.

AeroPress calls its design "3 in 1" and names the three parts on its product page for the AeroPress Clear: fast immersion, micro-filtration and air pressure.

  • Fast immersion. The grounds steep for 30 to 60 seconds in the maker's basic recipe. AeroPress says the short steep minimizes bitterness, acidity and over-extraction, which is what happens when the water keeps pulling compounds out of the coffee after the pleasant ones are already in the cup.
  • Micro-filtration. A thin round paper filter sits in a cap screwed onto the bottom of the tube, called the chamber. AeroPress says this step is for zero grit, meaning no fine particles of ground coffee in the cup.
  • Air pressure. When the plunger goes down, it traps a cushion of air above the coffee. Pushing on that air forces the liquid through the coffee and the filter quickly, and AeroPress credits this step with a smooth, full-bodied cup.

The AeroPress Clear is made from what the company calls crystal-clear, shatterproof Tritan, a plastic with the clear look of glass but not its fragility, and holds 10 ounces, or one to two cups. AeroPress says it comes with a scoop, a stirrer and paper filters (shop the AeroPress Clear). Because the chamber is clear, the whole brew is visible: the grounds blooming when the water hits them, the color of the coffee as it steeps and the level dropping as it is pressed.

The maker's recipe, step by step

The AeroPress instructions for the Original and Clear presses start with one heaping scoop of store-bought, medium ground coffee. The medium-fine version of the same recipe puts that heaping scoop at 16 to 18 grams.

  1. Heat the water. AeroPress says to heat water to 185°F (85°C) with a kettle, and that boiling water is fine for anyone without one.
  2. Set up the press. Separate the plunger from the chamber. Put a paper filter in the filter cap and screw the cap onto the chamber. Stand the chamber on a sturdy mug.
  3. Add coffee and water. Add the coffee and shake the chamber gently to level it. Pour water to the number 4 printed on the side of the chamber. A little coffee dripping into the mug at this point is normal.
  4. Stir and seal. Stir gently for about three seconds. Then, in the maker's words, quickly insert the plunger about half an inch into the chamber, then pull up slightly to create a vacuum to stop drip-through. A vacuum here means a pocket of lowered air pressure that holds the liquid in place.
  5. Wait. Wait 60 seconds.
  6. Press. Press down on the plunger with gentle, constant pressure, without pushing too hard, until a roar or hissing sound starts. That sound is the air pushing the last of the coffee through the bed of grounds.
  7. Clean up. Remove the filter cap. Over a sink or bin, push the plunger the rest of the way until the used grounds pop out as a round coffee puck. Rinse the cap and the plunger end under fresh water, and clean the press with gentle soap and a soft cloth every two weeks.

Grind size and steeping time

Grind size controls how fast extraction happens. Smaller particles expose more surface to the water, so a fine grind gives up its flavor faster than a coarse one. The AeroPress instructions build that into the recipe. With store-bought medium grind, the wait is 60 seconds. With a medium-fine grind, the wait drops to 30 seconds. The recipe pairs the finer grind with the shorter steep.

The Specialty Coffee Association's Golden Cup Standard calls for a solubles extraction yield of 18 to 22 percent. Extraction yield is the share of the ground coffee's weight that dissolves into the water. Grind, time and temperature are three dials that all move the same number. Moving any one of them changes the cup, so the simplest way to adjust is to change one dial at a time and taste the difference.

Water temperature, and brewing a mile high

The AeroPress target of 185°F matters in Denver. Water boils at a lower temperature as elevation rises, because there is less air pressing down on its surface. Colorado State University Extension lists the boiling point of water as 212°F at sea level and about 203°F at 5,000 feet. The National Center for Home Food Preservation at the University of Georgia lists 201°F at 6,000 feet. Denver sits about a mile, or 5,280 feet, above sea level, and the Colorado State Capitol marks that mile on its 13th step, so a Denver kettle at a full boil reads roughly 202°F.

A lower boil caps how hot a Denver kettle can get. For the AeroPress recipe, that cap makes almost no difference, because the maker's target already sits about 17 degrees below a Denver boil. The instructions also say boiling water is fine, so a Denver brewer following either path is working inside the maker's recipe.

Temperature can also matter less to the final taste than it seems. Researchers at the University of California, Davis, Mackenzie Batali, William Ristenpart and Jean-Xavier Guinard, made drip-brewed coffee at 87, 90 and 93°C (about 189, 194 and 199°F) and adjusted grind size, the ratio of coffee to water and the flow of water so that each batch reached the same strength and the same extraction yield. Writing in Scientific Reports in 2020, they found that across that range the brew temperature had no appreciable impact on the coffee's sensory profile, its taste and aroma as rated by a trained panel of 12 tasters. The study tested a drip brewer, not the AeroPress, but it points to a practical idea: if the water runs cooler, a slightly finer grind or a longer wait is a way to bring strength and extraction back to where they were.

A kettle that holds a set temperature removes the guesswork. Fellow describes the Stagg EKG Pro as an electric kettle with temperature control from 104°F to 212°F, a hold mode that keeps water hot for 15, 30, 45 or 60 minutes, a 30-ounce capacity and a gooseneck spout for slow pouring. Fellow also gives it an altitude setting to prevent boiling over by customizing the elevation for the user's location, and a built-in timer for pour-over and steeping, which covers the 30 or 60 second wait (shop the Fellow Stagg EKG Pro kettle). The Denver altitude cooking guide covers what the same thin air does to beans, candy and baking.

A Denver brew card

The card sets the maker's recipe beside the boiling points from the two university tables. The Denver boiling point is this guide's own estimate between the 5,000 and 6,000 foot figures, and changes in air pressure from the weather move it a little from day to day.

Step Maker's recipe In a Denver kitchen
Coffee 16 to 18 g, one heaping scoop Same
Grind and wait Medium: 60 seconds. Medium-fine: 30 seconds Same; a slightly finer grind or longer wait offsets cooler water
Water level To the 4 mark Same
Water temperature 185°F (85°C), or boiling water A full boil here is about 202°F, about 17°F above the target
Stir About 3 seconds Same
Press Gentle, constant pressure until the roar or hiss Same

Standard or inverted

The standard method is the one above: the press stands upright on the mug, filter end down. The inverted method turns it upside down. The plunger goes in first, the press stands on the plunger end, coffee and water go in through the open top, and the filter cap goes on last before the whole thing is flipped onto a mug and pressed.

AeroPress explains on its help center why people do this: to stop coffee dripping through before the steep is over, to control longer steeping times, and to use coarser grind sizes. The company also strongly discourages it. Brewing upside down makes the press less stable, it says, and prone to mishaps that can expose the brewer to burns from hot liquid.

The company offers two ways to stop drip-through with the press standing upright. The first is already in the basic recipe: setting the plunger about half an inch into the chamber holds the coffee in place, the way a finger over the end of a straw holds the liquid inside it. The second is the Flow Control Filter Cap.

The Flow Control Filter Cap

The Flow Control Filter Cap replaces the standard cap on the bottom of the press. AeroPress says it has a pressure-actuated valve, meaning a small valve that stays shut until pressure opens it. The valve does not open until pressing begins, so no coffee drips through during the steep, however long it runs. That gives the brewer full control over grind size and brewing time, including the coarser grinds and longer steeps that the inverted method is used for.

AeroPress lists a few other points on its page for the cap:

  • Crema. With a paper filter and dark-roast coffee, the company says the cap creates espresso-like crema, the thin layer of fine foam on top of a shot of espresso.
  • Filters. It works with paper and metal filters, in the Standard size.
  • Fit. It fits the AeroPress Original, Go, Clear, Premium, Steel and Go Plus, but not XL size coffee makers.
  • Cleaning. It cleans with a quick rinse and can go on the top rack of the dishwasher. A used paper filter can be brushed off with the end of the stirrer.

The company says the cap opens up recipes from classic to cold brew to espresso-style drinks and lattes (shop the AeroPress Flow Control Filter Cap).

What the paper filter does

The filter is the smallest part of the press and does a large share of the work. AeroPress describes its paper micro-filters as ultra-thin and tightly woven, with micro-sized holes, and the company credits this micro-filtration with a cup that has zero grit. AeroPress also says the paper absorbs bitter-tasting oils for a cleaner, brighter cup and preserves clarity and delicate flavor, especially in light and medium roasts. Clarity here means a cup in which separate flavors are easy to pick out, rather than a heavier, rounder texture.

The filters are made from natural, unbleached, food-safe paper, and AeroPress describes them as biodegradable and home compostable, so a used filter can go into the compost with the coffee puck (shop AeroPress paper micro-filters).

Three ways to change the cup

  • For a quicker cup, keep the dose and stir, and go one step finer on the grind with the 30 second wait.
  • For a longer steep, use a coarser grind with the Flow Control Filter Cap, which keeps the coffee in the chamber until pressing begins.
  • For a latte-style drink, brew with a paper filter and a dark roast through the Flow Control Filter Cap, then pour the coffee over warm milk.

For the beans, shop coffee. The press, its caps and its filters sit together in one place (shop the AeroPress collection). The shop is at 263 Josephine Street in Cherry Creek, Denver, where visitors can ask staff questions, and products ship nationwide from theambrosianpantry.com.

The AeroPress looks like a gadget, but it is a lesson in how coffee works. Every cup is the same three choices, grind, time and heat, settled in a few minutes, and because the press puts each of those dials in the brewer's hands, it teaches as it brews. A Denver kitchen loses a few degrees at the kettle and need not lose anything in the cup, because a recipe built on 185°F was never asking for a full boil in the first place.

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