Why a double filter basket gives the best extraction and is essential for adjusting your coffee grinder

Why a double filter basket gives the best extraction (and is essential for adjusting your grinder)

Anyone who wants to adjust their coffee grinder for the perfect espresso must make one fundamental choice: do you work with a single or a double filter basket?

Many home baristas simply use whatever is in the piston ( portafilter ). But if you want technically correct adjustments—for flavor, extraction, and brew time—the double portafilter is always the right choice .

In this article I will explain exactly why.

What happens during espresso extraction?

An espresso machine operates at approximately 9 bar of pressure . This means that hot water is forced through a compact bed of ground coffee with considerable force.

That pressure remains constant.
What is not constant is:

• The grind
• The distribution of the coffee
• The resistance in the filter basket
• The geometry of the container

And it is precisely this last factor that is often underestimated.

Single vs. Double Filter Basket : The Fundamental Difference

1️⃣ Double filter basket

Feature: straight walls that run straight down.

That means:

• The resistance is the same everywhere
• The water experiences a uniform counter pressure
• The extraction is proportional

All coffee particles are affected by the water in the same way.

Result:
→ Balanced extraction
→ Controllable taste
→ Reliable adjustment of your grinder

2️⃣ Single filter basket

Feature: tapered walls (funnel shape).

Water always seeks the path of least resistance.

What happens at 9 bar pressure?

• Under-extraction occurs in the corners
• Over-extraction occurs in the middle
• Extraction is unevenly distributed

Result in taste:

Problem	Taste result
Underextraction	Too many acids
Overextraction	Bitterness, burnt notes

So you get two flavors in one shot at once . This makes correct adjustment virtually impossible.

Why you should always set your grinder to a double bowl

If you want to optimize your grind, you need two measurement points:

1. Lead time (25–30 seconds)
2. Taste

With a double bucket you can work technically reliably:

• You dose approximately 18 grams
• You're aiming for a ratio of about 1:2 (or 1:3)
• You see if you can get out within 25–30 seconds

Then you taste it.

*There are different containers for different brands. Read the blog post: How many grams of coffee do I need in my filter holder?

Adjusting to taste: how to do it correctly

When you're within the right time, the real work begins: tasting .

Espresso too sour?

• This indicates under-extraction (unless you are working with a single origin African coffee)
• Adjust your grind a little finer

You extend the extraction, which releases a little more bitterness and creates balance.

Espresso too bitter?

• This indicates over-extraction (unless you are using a Robusta coffee bean)
• Set your grinder to a slightly coarser setting

You let the first extraction part (where acids are released) dominate a little more.

Important:
You always work in small steps.

Why an espresso machine is actually built “for two”

A piston machine is designed to:

• Brew two espressos at the same time
• Or use one double espresso as a base for:
  • Cappuccino
  • Latte
  • Americano
  • Flat white

Technically, the machine is optimized for the double-cup design. The single-cup design is more of a practical option—not an ideal extraction solution.

Conclusion

Do you want:

• Adjusting your grinder correctly
• Understanding extraction technically
• Gaining control over taste
• Making consistent espresso

Then always use a double filter basket .

The straight design provides even back pressure, a balanced extraction and a reliable base for adjusting the flavour.

You do not adjust the grinder for time alone.
You adjust it to balance in the cup .

And that balance starts with the right container.

Frequently Asked Questions:

1. Can I also adjust my coffee grinder with a single filter basket?

Technically it is possible, but it is not reliable.

A single filter basket has tapered walls, which creates an uneven distribution of resistance. At 9 bar of pressure, water seeks the path of least resistance, which can lead to simultaneous under- and over-extraction.

This makes it virtually impossible to correctly calibrate your grind purely based on taste and extraction time.
For consistent adjustment, a double filter basket is always the right choice.

2. How many grams of coffee exactly should go into a double filter basket?

This depends on the type of basket, but for a standard 58mm double filter basket this is usually:

17–19 grams of coffee

More important than the exact gram count is:

• That you dose consistently

• That you work with a fixed ratio (for example 1:2)

• That you come out within 25–30 seconds

Only then do you fine-tune the taste.

3. Why does my espresso taste sour even though the brew time is correct?

If you're within 25–30 seconds and your espresso still tastes sour, there could be several reasons:

• Your grind is just a little too coarse

• Your temperature is too low

• You use a lightly roasted single origin (for example African profile)

• You are experiencing channeling due to poor distribution

The lead time is a guideline — taste always remains the decisive criterion.

4. Is a double filter basket also better if I only want to drink one espresso?

Yes.

You can simply make a double espresso and:

• Drink both shots separately

• Or use one shot and throw the rest away (technically a waste, but extraction-wise correct)

• Or work with a shorter ratio (for example 1:1.5)

The machine is designed for a double-bowl setup. The single-bowl setup is primarily a practical addition, not a technically ideal extraction solution.

5. What's more important when adjusting my grinder: time or taste?

Taste.

The time (25–30 seconds) is a checkpoint to see if you are in the correct extraction zone.
But ultimately you adjust your grinder to balance in the cup:

• Too sour → grind slightly finer

• Too bitter → grind slightly coarser

Small steps. Always taste.
Technology supports taste — not the other way around.

6. What if I still want to drink a single espresso?

Always first adjust your coffee grinder with a double filter basket — to the fresh espresso blend or single origin you are using.

Why?

The double bowl provides even counter pressure and therefore technically reliable extraction. This allows you to determine the optimal grind size based on:

• Cycle time (±25–30 seconds)

• Ratio (for example 1:2)

• Taste balance

Once your grind is set correctly, you can then switch to your single filter basket.

Important to understand:

A single cup doesn't provide the same uniform extraction as a double cup. The tapered shape always results in a slightly less even flow.

But — and this is crucial — your grind size will remain correctly matched to the coffee you are using.

So you compromise a little on extraction precision, but not on the basic adjustment of your grinder.

In practical terms this means:

• First calibrate technically correctly with a double container

• Then use only one cup for your single espresso

• And accept that the extraction is a little less perfect

This way you can work in a controlled manner, without disturbing your entire setup every time.