Jonathan Gagné

Astrophysicist and coffee researcher; author of The Physics of Filter Coffee and The Physics of Espresso, and writer of the Coffee ad Astra blog on brewing science and equipment.

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The Importance of Bed Depth 28 Nov 2025

What they believe

Dripper diameter, with other brew variables held fixed, does not change extraction or taste — only batch size.

changing the dripper diameter, keeping all other important variables fixed, has no impact on the brew mechanics and the resulting cup, in an "idealized" scenario

coffeeadastra.comSaid 28 Nov 2025This on korrents
Conical burrs tend to be less unimodal and less uniform than flat burrs, though the two overlap a lot.

Conical burrs appear on average less unimodal and less uniform, although there is a large overlap meaning that one can easily find a specific flat burr that is less unimodal and less uniform than a specific conical burr.

coffeeadastra.comSaid 21 Sept 2023This on korrents

The bold line is korrents’ wording; the quote is theirs. These 2: what they wrote before what they said aloud, one per source, newest first.

All 11 beliefs, on korrents

Feed

As its own page →

Everything, newest first — across every channel.

Sources

28 November 2025

Jonathan GagnéKorrents 28 Nov 2025

From one piece The Importance of Bed Depth 3 beliefs · coffeeadastra.com

korrents.com
A deeper coffee bed reduces astringency by trapping long molecules on particle surfaces, not by pore-size filtration.

Their words

the coffee bed would act on these molecules by filtering them out a bit like oxygen adsorbers keep oxygen in; it just provides a gigantic maze of free surface area for them to stick on, and hopefully the microscopic fluid velocity is gentle enough to not drag them along.

The Importance of Bed Depthcoffeeadastra.com
korrents.com
Coffee bed depth, unlike bed width, significantly affects flavor in a way other brew variables cannot easily compensate for.

Their words

the depth of a coffee bed, contrary to the width of the coffee bed, is a variable that impacts the flavor of the coffee being brewed significantly, and in a way that you cannot easily compensate for by changing other brew variables.

The Importance of Bed Depthcoffeeadastra.com
korrents.com
Dripper diameter, with other brew variables held fixed, does not change extraction or taste — only batch size.

taste

Their words

changing the dripper diameter, keeping all other important variables fixed, has no impact on the brew mechanics and the resulting cup, in an "idealized" scenario

The Importance of Bed Depthcoffeeadastra.com

Jonathan GagnéRecommends 28 Nov 2025

Usestheir ownrcmnd.app
Pulsar Mini

Their words

In other words, I still use exactly the same recipe that I developed for the Pulsar when I brew with the mini, I just brew with a dose smaller by a factor 0.6 (e.g., 15 grams instead of 25).

coffeeadastra.com

14 August 2025

Jonathan GagnéBlog 14 Aug 2025

The Physics of Espresso is out !!
physics

9 March 2024

Jonathan GagnéBlog 9 Mar 2024

Recent Insights into Espresso Dynamics April 14 Chicago Conference

21 September 2023

Jonathan GagnéKorrents 21 Sept 2023

From one piece What I learned from analyzing 300 particle size distributions for 24 espresso grinders 3 beliefs · coffeeadastra.com

korrents.com
Burr geometry matters more than burr size for how uniform and unimodal a grinder's output is.

Their words

It therefore appears that burr geometry may be more important than burr size in determining unimodality and uniformity.

coffeeadastra.com
korrents.com
Grinders that produce fewer fines (more unimodal) also tend to produce more uniform particle sizes.

Their words

Contrary to popular hearsay, more unimodal grinders appear to also be more uniform on average.

coffeeadastra.com
korrents.com
Conical burrs tend to be less unimodal and less uniform than flat burrs, though the two overlap a lot.

Their words

Conical burrs appear on average less unimodal and less uniform, although there is a large overlap meaning that one can easily find a specific flat burr that is less unimodal and less uniform than a specific conical burr.

coffeeadastra.com

13 September 2023

Jonathan GagnéRecommends 13 Sept 2023

Lovedtheir ownrcmnd.app
Pulsar dripper

Their words

After years of development, I'm super happy to report that the dripper I dreamed of for so long is finally out!

coffeeadastra.com
Likedrcmnd.app
Lvl-10 dripper

Their words

I was super excited when I saw the Lvl-10 dripper, because it was very close to what I wanted to achieve, and as I expected, it performed very well in terms of extraction quality.

coffeeadastra.com

1 August 2022

Jonathan GagnéKorrents 1 Aug 2022

From one piece The Mechanism Behind Astringency in Coffee 3 beliefs · coffeeadastra.com

korrents.com
The compounds responsible for astringency in coffee require very high water temperatures to dissolve efficiently.

Their words

The case of astringent compounds is particularly interesting, because they require a very high temperature to be dissolved efficiently in water.

The Mechanism Behind Astringency in Coffeecoffeeadastra.com
korrents.com
Grinding coffee too fine liberates more astringent compounds by breaking more coffee cells, causing astringency no matter how evenly water flows.

Their words

Grinding too fine will liberate a lot more astringent compounds by breaking more coffee cells, which will result in an astringent cup regardless of how even the water flows through the coffee bed.

The Mechanism Behind Astringency in Coffeecoffeeadastra.com
korrents.com
Avoiding astringency in coffee is fundamentally a filtration problem rather than simply a matter of flow evenness.

Their words

Therefore, avoiding astringency is not directly a matter of flow evenness, it is actually a filtration problem !

The Mechanism Behind Astringency in Coffeecoffeeadastra.com

16 July 2022

Jonathan GagnéKorrents 16 Jul 2022

From one piece More Even Espresso Extractions 2 beliefs · coffeeadastra.com

korrents.com
Flat burr grinders tend to deposit ground coffee preferentially on one side of the portafilter, an effect worsened by higher grinder RPM.

design

Their words

flat burrs tend to send the coffee preferentially on one side of the portafilter (to the right side with the design of EG-1), an effect probably worsened by the use of high rpm.

More Even Espresso Extractionscoffeeadastra.com
korrents.com
Adding hydraulic resistance beneath an espresso puck reduces channeling by slowing the flow of water and making it more even across the coffee bed.

Their words

I now suspect that adding a source of hydraulic resistance under the puck that is non-negligible compared with the espresso puck itself is desirable to reduce the impact of channels because it slows down the flow of water where it would tend to become otherwise too fast and as a consequence less even across the surface of the coffee bed.

More Even Espresso Extractionscoffeeadastra.com

18 March 2022

Jonathan GagnéBlog 18 Mar 2022

The Physics of Coffee Class
physics

23 October 2021

Jonathan GagnéBlog 23 Oct 2021

Restraining Flow to Mitigate Channels

8 September 2021

Jonathan GagnéBlog 8 Sept 2021

Reaching Fuller Flavor Profiles with the AeroPress

The whole feed →

Beliefs

Korrents What they believe 11 beliefs — each backed by an exact quote.
Each is a — compiled by korrents.com, not by them: the one-line wordings are korrents', the quotes are theirs.
Recent
- Dripper diameter, with other brew variables held fixed, does not change extraction or taste — only batch size.
  
  changing the dripper diameter, keeping all other important variables fixed, has no impact on the brew mechanics and the resulting cup, in an "idealized" scenario
  
  The Importance of Bed Depth Said 28 Nov 2025
  
  Full record — everyone who holds this →
  
  taste
- Coffee bed depth, unlike bed width, significantly affects flavor in a way other brew variables cannot easily compensate for.
  
  the depth of a coffee bed, contrary to the width of the coffee bed, is a variable that impacts the flavor of the coffee being brewed significantly, and in a way that you cannot easily compensate for by changing other brew variables.
  
  The Importance of Bed Depth Said 28 Nov 2025
  
  Full record — everyone who holds this →
- A deeper coffee bed reduces astringency by trapping long molecules on particle surfaces, not by pore-size filtration.
  
  the coffee bed would act on these molecules by filtering them out a bit like oxygen adsorbers keep oxygen in; it just provides a gigantic maze of free surface area for them to stick on, and hopefully the microscopic fluid velocity is gentle enough to not drag them along.
  
  The Importance of Bed Depth Said 28 Nov 2025
  
  Full record — everyone who holds this →
Show 8 more

Conical burrs tend to be less unimodal and less uniform than flat burrs, though the two overlap a lot.

Conical burrs appear on average less unimodal and less uniform, although there is a large overlap meaning that one can easily find a specific flat burr that is less unimodal and less uniform than a specific conical burr.

What I learned from analyzing 300 particle size distributions for 24 espresso grinders Said 21 Sept 2023

Full record — everyone who holds this →

Grinders that produce fewer fines (more unimodal) also tend to produce more uniform particle sizes.

Contrary to popular hearsay, more unimodal grinders appear to also be more uniform on average.

What I learned from analyzing 300 particle size distributions for 24 espresso grinders Said 21 Sept 2023

Full record — everyone who holds this →

Burr geometry matters more than burr size for how uniform and unimodal a grinder's output is.

It therefore appears that burr geometry may be more important than burr size in determining unimodality and uniformity.

What I learned from analyzing 300 particle size distributions for 24 espresso grinders Said 21 Sept 2023

Full record — everyone who holds this →

Avoiding astringency in coffee is fundamentally a filtration problem rather than simply a matter of flow evenness.

Therefore, avoiding astringency is not directly a matter of flow evenness, it is actually a filtration problem !

The Mechanism Behind Astringency in Coffee Said 1 Aug 2022

Full record — everyone who holds this →

Grinding coffee too fine liberates more astringent compounds by breaking more coffee cells, causing astringency no matter how evenly water flows.

Grinding too fine will liberate a lot more astringent compounds by breaking more coffee cells, which will result in an astringent cup regardless of how even the water flows through the coffee bed.

The Mechanism Behind Astringency in Coffee Said 1 Aug 2022

Full record — everyone who holds this →

The compounds responsible for astringency in coffee require very high water temperatures to dissolve efficiently.

The case of astringent compounds is particularly interesting, because they require a very high temperature to be dissolved efficiently in water.

The Mechanism Behind Astringency in Coffee Said 1 Aug 2022

Full record — everyone who holds this →

Adding hydraulic resistance beneath an espresso puck reduces channeling by slowing the flow of water and making it more even across the coffee bed.

I now suspect that adding a source of hydraulic resistance under the puck that is non-negligible compared with the espresso puck itself is desirable to reduce the impact of channels because it slows down the flow of water where it would tend to become otherwise too fast and as a consequence less even across the surface of the coffee bed.

More Even Espresso Extractions Said 16 Jul 2022

Full record — everyone who holds this →

Flat burr grinders tend to deposit ground coffee preferentially on one side of the portafilter, an effect worsened by higher grinder RPM.

flat burrs tend to send the coffee preferentially on one side of the portafilter (to the right side with the design of EG-1), an effect probably worsened by the use of high rpm.

More Even Espresso Extractions Said 16 Jul 2022

Full record — everyone who holds this →

design
All 11 beliefs →

What is a korrent?

A korrent is a belief a person has stated in their own words: one sentence stating the claim, backed by a quote and a source, kept at korrents.com.

Under a name here, the quoted block is what they actually said. The korrent beneath it is the claim those words support, in korrents' wording — tap it to see the record, its source, and who else holds it.

Nobody here wrote their own korrents. They are compiled from public statements, and a person can change their mind, which is recorded too.

Recommends rcmnd

rcmnd What they recommend 5 things — each backed by an exact quote.
Compiled by rcmnd.app, not by them: the quotes are theirs, and each links to the post it was copied from.
Recent
- Uses Pulsar Mini 28 Nov 2025
  
  In other words, I still use exactly the same recipe that I developed for the Pulsar when I brew with the mini, I just brew with a dose smaller by a factor 0.6 (e.g., 15 grams instead of 25).
  
  coffeeadastra.com 28 Nov 2025
  
  their own
  
  What others say about Pulsar Mini →
- Liked Lvl-10 dripper 13 Sept 2023
  
  I was super excited when I saw the Lvl-10 dripper, because it was very close to what I wanted to achieve, and as I expected, it performed very well in terms of extraction quality.
  
  coffeeadastra.com 13 Sept 2023
  
  What others say about Lvl-10 dripper →
- Loved Pulsar dripper 13 Sept 2023
  
  After years of development, I'm super happy to report that the dripper I dreamed of for so long is finally out!
  
  coffeeadastra.com 13 Sept 2023
  
  their own
  
  What others say about Pulsar dripper →
Show 2 more

Mixed on AeroPress 7 Sept 2021

While I have enjoyed the AeroPress a lot in the past especially when travelling, I have always had one big complaint about it: getting a thick coffee bed to minimize uneven flow when pressing out the water limits the brew ratios that can be used.

coffeeadastra.com 7 Sept 2021

What others say about AeroPress →

Recommends James Hoffmann's AeroPress videos 7 Sept 2021

I highly recommend watching all three of his videos, because the tests and discussions he presented are of a very high quality.

coffeeadastra.com 7 Sept 2021

What others say about James Hoffmann's AeroPress videos →
All 5 recommendations →

Where they publish

Blog Coffee ad Astra His blog on the physics and chemistry of coffee brewing and equipment.
Open coffeeadastra.com
Recent
- The Importance of Bed Depth 28 Nov 2025 In this post, I discuss the impact of bed depths on brewing filter coffee, and how this impacts my favorite brew parameters with the Pulsar and the Pulsar mini, and I offer some reasons why I think bed depths affects fl…
- The Physics of Espresso is out !! 14 Aug 2025 Hello all ! I am so thrilled to announce that my second book The Physics of Espresso is finally out ! This one took a while longer than I expected, and you’ll understand why when you get your hands on it. It contains hu…
- Recent Insights into Espresso Dynamics April 14 Chicago Conference 9 Mar 2024 I will be presenting a conference on the topic of espresso dynamics during SCA 2024 in Chicago !
Show 7 more

What I learned from analyzing 300 particle size distributions for 24 espresso grinders 21 Sept 2023 This post presents a deep analysis of 300 particle size distributions for various espresso grinders
The Pulsar Dripper 13 Sept 2023 This post presents the Pulsar dripper with my current favorite brewing recipe.
The Mechanism Behind Astringency in Coffee 1 Aug 2022 In this post, I discuss my updated understanding of the mechanism by which astringent compounds can be extracted from coffee.
More Even Espresso Extractions 16 Jul 2022 In this post, I talk about ways in which I have recently improved my puck preparation for espresso.
The Physics of Coffee Class 18 Mar 2022 Announcing a coffee class during the Boston SCA expo
Restraining Flow to Mitigate Channels 23 Oct 2021 In the past weeks, I have been experimenting with the AeroPress combined with the Prismo attachment, and I tried one small hack that produced a surprising result. I inserted a pasta strainer mesh like the one I describe…
Reaching Fuller Flavor Profiles with the AeroPress 8 Sept 2021 In this post, I discuss the AeroPress and how it can be used to reach flavor profiles similar to cuppings and high-EY pour overs.
Link verified 5 Sept 2026. Recent items update automatically from the channel.
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