Bed Depth: Why It Matters

By Scott Rao

Republished by ST. DION Coffee with permission.

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From ST. DION

At ST. DION, we believe exceptional coffee comes from understanding the fundamentals. In this article, Scott Rao explains why coffee bed depth is often an overlooked variable that can have a significant impact on extraction quality and cup clarity.

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Bed Depth: Why It Matters

As third-wave coffee has evolved over the past 25 years, several long-term trends have emerged. Roasts have become lighter, roasters are using fresher green coffee than ever before, café menus have become more focused, and filter coffee servings—particularly in the United States—have become smaller.

These trends have undoubtedly improved cup quality, but brewing increasingly smaller doses has also introduced new challenges.

I’m all for brewing small amounts of coffee. I’d rather taste several small portions of different coffees than one large mug of one coffee. However, I often see cafés trying to batch brew less than two liters in commercial brewers or preparing very small pourovers, such as 15 g doses in a Kalita 185, NextLevel Pulsar, or Filter3. The problem is that these brews often create coffee beds that are simply too shallow.

Why Does Bed Depth Matter?

If a coffee bed is too deep, a much coarser grind is required to maintain proper flow. While the resulting cup may still be enjoyable, extraction efficiency is reduced, leaving more soluble material behind.

More commonly, brewers fail to grind coarse enough for deep beds. This leads to clogged filters, increased channeling, and astringent flavors. The problem is especially common with grinders that produce excessive fines and with large batch brews.

Shallow coffee beds create a different issue.

Let’s assume that some degree of channeling occurs during nearly every percolation brew. What matters is not simply whether channels form, but whether they reach the bottom of the coffee bed.

Channels that terminate within the coffee bed are generally harmless. Channels that reach the filter, however, can carry larger, astringency-causing compounds into the cup.

Because shallow beds provide fewer opportunities for channels to stop naturally, they are generally more prone to producing astringent brews.

Finding the Sweet Spot

The traditional guideline for commercial batch brewing was maintaining a coffee bed approximately 3–5 cm deep.

For single-cup brewers, ideal bed depth depends on brewer geometry, filter design, and coffee characteristics. Based on experience with dense, lightly roasted coffees, I’ve found these dose ranges to work particularly well:

Brewer

Recommended Dose

NextLevel Pulsar

30–35 g

Kalita 185

25–30 g

V60

20–25 g

Fellow Stagg X

25 g

Kalita 155

15–18 g

Pulsar Mini

15 g

AeroPress

18–20 g

Filter3

20–22 g

These recommendations apply to dense, lightly roasted coffees. I cannot say what is optimal for darker roasts.

Of course, any dose can be used in any brewer. The point is simply that when bed depth becomes substantially shallower than these recommendations, the likelihood of astringency increases.

These doses represent practical “safe zones,” providing sufficient bed depth while allowing a grind fine enough to achieve high extractions without excessive channeling.

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About Scott Rao

Scott Rao is one of the specialty coffee industry’s most respected authors, educators, and consultants. His work on coffee roasting, extraction, and brewing has influenced coffee professionals around the world.

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Originally written by Scott Rao. Republished by ST. DION Coffee with permission.

Original article: https://www.scottrao.com/blog/2025/11/11/bed-depth-why-it-matters