1. Introduction: The AeroPress Debate and James Hoffmann's Videos

James Hoffmann's recent AeroPress videos sparked a huge discussion in the coffee community. The author notes that "it's rare to find so little disagreement in a deep discussion about coffee extraction methods," and says Hoffmann's experiments and conclusions align well with his own physical understanding of brewing.

"Everything James argued and concluded fit perfectly with my current understanding of the physics of coffee extraction."

Reference videos:

• Part 1 – The AeroPress
• Part 2 – Understanding the AeroPress
• Part 3 – The Ultimate AeroPress Technique

2. The Limitations of the AeroPress and the Author's Dilemma

The author, who frequently used the AeroPress while traveling, had one persistent frustration. A thick coffee bed is needed for water to flow through evenly, which limits the usable brew ratio. For example, with 18 g of coffee, only about 260 mL of water fits, capping the ratio at roughly 1:14.

This tends to produce coffee with bright acidity but insufficient sweetness — a classic sign of underextraction.

3. Discovering the Potential of Long Immersion Times

Alongside Hoffmann's videos, the author came across a UC Davis research paper on "very long immersion brewing." The paper showed that extraction yield — how much material is dissolved from the grounds — is nearly unaffected by brew ratio when immersion lasts an hour or more.

"Reading that paper made me rethink the AeroPress problem. I wanted to try a much longer immersion time."

Key idea:

• As coffee grounds and water approach near-equilibrium, the chemical concentration difference between the inside of the particles and the slurry diminishes.
• This means you can achieve a flavor profile similar to a high-extraction drip brew that has nearly run to completion.

4. A New Perspective on Brewing Temperature

In his videos, Hoffmann mentions an interesting observation: preference for extraction temperature shows a "double hump."

• Brews taste best near 80°C and again above 90°C, with a dip in preference for temperatures in between.
• The author had never brewed AeroPress above 90°C, partly assuming the AeroPress's good insulation was a limiting factor.

5. The Experiment: The Shocking Results of 99°C and a 10-Minute Immersion

The author tries something he had never attempted before: 99°C water and a 10-minute immersion.

"I was stunned by the extreme sweetness in the cup. So I decided to experiment further and develop a repeatable recipe."

• Hoffmann noticed only modest improvement at 2–4 minutes, but the author felt that 10 minutes was well worth it for home brewing.

6. The Complexity of Extraction: The Cause of Astringency

Even after 10 minutes of immersion, the author found that astringency could still appear when pressing the plunger.

"Even though the slurry was already saturated with coffee compounds, pressing the plunger hard still produced astringency. That was genuinely surprising."

• The author hypothesizes that large molecules called polyphenols are the culprit.
• These molecules cling to the surface of coffee particles and can be forced into the cup by rapid localized flow rates (channeling) during pressing.

7. Preventing Astringency: A Flat Coffee Bed and Gentle Plunger Pressure

Avoiding astringency comes down to not pressing the plunger hard and keeping the coffee bed flat.

"James also noted that brews where he had to press hard tasted much worse — which matches my experience exactly."

• Grind size and particle distribution matter: too coarse and 10 minutes of immersion won't extract enough; too fine and the plunger becomes unworkably hard to press.
• A narrow particle size distribution with fewer fines is ideal.

8. Brewing Tips: The Importance of Stirring and Swirling

• Avoid circular stirring!

  "Stirring in circles causes the coffee bed to pile up in a dome shape, so when you press the plunger, water only flows along the edges. This resulted in a flat, astringent cup."

• Back-and-forth stirring wets the grounds more evenly.
• Swirling once after stirring, and again at the 5-minute mark, helps the bed settle flat.

9. The Advantages of the Prismo Attachment

• Using the Fellow Prismo prevents side bypass (water escaping around the coffee bed) and reduces filter clogging.
• Tip:
  • When using the Prismo, pour in half the water first, add the coffee on top, then pour the remaining water.

    "This keeps the fines suspended, reduces filter clogging, and lets you use a finer grind without problems."

10. The Author's AeroPress Recipe (Summary)

1. Place the AeroPress on a sturdy mug for stability.
2. Insert a dry filter and screw the cap on firmly.
3. Add 18 g of coffee and shake gently side to side to level it.
   • With Prismo: pour in half the water first, then add the coffee on top.
4. Pour 100°C water until the AeroPress is full (approximately 260 g).
5. Stir back and forth (no circular motion).
6. Rest the plunger lightly on top.
7. Remove from the scale and swirl once.
8. At 5 minutes, swirl once more.
9. At 9 minutes (or later), press the plunger very gently.

"With this recipe I achieved an average extraction yield of 23.5% — calculated only from the compounds actually dissolved in the cup."

11. Changes in Extraction Yield and Flavor

• With long immersion, the concentration inside the coffee particles and in the slurry converge toward equilibrium, producing a flavor profile similar to high-yield drip (percolation) brewing.
• The result was noticeably sweeter, and sweeter than comparable brews from other methods.

12. AeroPress Characteristics: Undissolved Solids and Pressure

• Because the AeroPress uses pressure (0.5–1 bar), more undissolved solids end up in the cup compared to regular drip (0.008 bar).
• However, the author says he "did not find that this worsened the flavor or diminished the character of the beans."

13. Cautions for Grind Size and Roast Level

• Too fine a grind makes astringency likely; too coarse risks underextraction.
• For dark roasts, brewing at 100°C can amplify bitterness and burnt notes — the author recommends lowering the temperature in that case.

14. Experimenting with Re-Stirring Mid-Brew

• The author tried opening the cap at 5 minutes and stirring again, but found that the coffee bed did not settle flat again, making astringency worse.
• He concludes that swirling only at 5 minutes is more effective.

15. Similarities to Cupping

• The author notes a strong resemblance between this long-immersion method and cupping — the industry-standard technique professionals use to evaluate coffee quality.
• He argues that the long immersion time in cupping serves not just to let the brew cool, but also to achieve near-equilibrium extraction.

16. TL;DR & Practical Tips

• Try immersing for 10 minutes or more.

  "The AeroPress can produce a flavor profile similar to high-extraction drip coffee."

• Use 100°C water (especially for light roasts).
• Press the plunger very gently.
• Keep the coffee bed flat.

  "Even when the slurry is saturated, uneven flow can still produce astringency."

• Use a Prismo if you have one.

  "It prevents side bypass and reduces filter clogging."

• This method produces flavors similar to high-extraction drip or cupping, but roughly 3% of the coffee is lost to the concentrated water retained in the grounds (about 0.5 g per 18 g dose).

Key Terms

• AeroPress
• Immersion Time
• Extraction Yield
• Astringency
• Polyphenol
• Plunger Pressure
• Flat Coffee Bed
• Prismo
• Swirling
• Grind Size
• Fines
• High Extraction Yield
• Cupping
• Brew Ratio
• Undissolved Solids

Closing

This piece is an excellent resource that takes a scientific and experimental approach to drawing out deeper, sweeter flavors from the AeroPress. Just remember: 10-minute immersion, 100°C water, gentle plunger pressure, and a flat coffee bed — and your AeroPress brews will reach a whole new level! Feel free to ask any questions 😊