Conical or Flat Burrs? An Experiment With Frozen Coffee

Is Freezing Coffee Still a Cardinal Sin?

In short, the answer is no, it never was, but we were doing it all wrong. So, the coffee enthusiasts who once swore that freezing coffee was a disaster were correct in a way. Oh, how times have changed! Within the last decade or so, coffee professionals and scientists discovered that properly freezing coffee can yield serious benefits—extending shelf life and improving grind consistency and extraction. Just promise us you won’t throw an open bag of beans in your fridge or freezer. That is not the way! Check out our previous coffee-freezing experiment for a refresher on the benefits of freezing coffee.  

Freezing coffee beans makes them more brittle, which changes how they shatter when ground. This leads to a more uniform particle size and, in turn, better and more consistent extractions.

But here’s the question we’re putting to the test: Does freezing coffee have an even more significant impact when using a conical burr grinder compared to a flat burr grinder?

Conical vs. Flat Burrs: Why Would It Matter?

If you’re wondering why there would be any difference, that's a fair question. The key lies in how these two types of grinders produce coffee grounds.

• Flat burrs tend to create a mono-modal particle size distribution. This means most coffee particles are roughly the same size, with a few smaller and larger ones mixed in.

• Conical burrs, on the other hand, create a bi-modal distribution. Instead of one peak, there are two—one for coarser particles and another for finer ones. This difference in particle size distribution is one of the main reasons why conical and flat burr grinders create different flavor profiles.

While Charles is more partial to conical burrs, he found that their tendency to produce more fines can make extractions a bit finicky. The hypothesis? Freezing beans might help smooth out that inconsistency, making conical burr extractions more reliable and even improving flavor clarity.

The Experiment

To test this, we used two high-quality single-dosing grinders:

1. Eureka Mignon Oro (65mm flat stainless steel burrs)

2. Weber KEY (83mm conical TiN-coated Mazzer burrs)

We prepared 10 doses for each grinder:

• 5 doses were kept at room temperature

• 5 doses were frozen before grinding

Next, we pulled espresso shots with each dose, measuring total dissolved solids (TDS) with a refractometer and calculated the extraction percentages. Refresher: a refractometer tells you how much coffee is in your coffee. Based on previous research, we expected increased extraction for both grinders when using frozen beans. But if the theory held, the effect would be stronger with the conical burr grinder.

The Results: Was Professor Charles Right?

Short answer: Yes! The data backed up his hypothesis.

Flat Burr (Eureka Mignon Oro)

• Room Temp Beans → 19.7% extraction

• Frozen Beans → 20.0% extraction

• Increase: 1.5%

That’s a minor improvement, but if you’re a coffee nerd chasing every last drop of flavor, 1.5% can be extremely impactful on espresso outcomes, including flavor, body, and clarity. 

Conical Burr (Weber Key)

• Room Temp Beans → 18.1% extraction

• Frozen Beans → 18.9% extraction

• Increase: 3.9%

A nearly 4% boost in extraction is a massive improvement. Not only that, but the difference in taste was far more noticeable. The frozen conical burr shots were smoother, with less of the lingering bitterness that sometimes comes with imperfect extractions.

Should You Freeze Your Beans?

This was a small test, but the results suggest that freezing beans can be beneficial if you’re using a conical burr grinder. When dialing in espresso, every method of controlling extraction is another tool in your toolbox. You won’t use every tool for every shot, but it’s good to have options—and unlike a 10mm socket, you can’t lose the concept of freezing coffee.

If you have a conical burr grinder, we highly recommend giving frozen beans a try. If you do, let us know what you think in the comments. And if you’re always looking for ways to tweak your coffee routine, well, you’re in good company. Cheers!

Further Reading:

• WEBER WORKSHOPS Bean Cellar: Experimenting with Freezing Coffee