What Makes a Good Coffee? Understanding Extraction Yield with the Atago Refractometer

By Tolga Seçkin October 5, 2026
Extraction Yield article cover

You finish your cup, and can’t help but think that something special was there — sweetness, a kind of balance, the pull to drink it again. But you can't quite say why it worked. Do you leave that to chance, or do you try to replicate the experience? That's the question Atago is built to answer.

Taste vs. Data

In coffee, "good" is often treated as something personal — it depends on the origin, the barista, or how your morning is going. But decades of research by the Specialty Coffee Association (SCA) point to something more concrete: good coffee has a measurable definition. That definition lives in a number called Extraction Yield. A coffee bean holds hundreds of compounds — acids, sugars, lipids, amino acids. However, you don't want all of them in your cup. When the right percentage is in place, flavour lands in balance. Too little or too much, and something goes wrong. Finding that window consistently is what the measurement is for.

What Is Extraction Yield and Why Does It Matter?

Extraction Yield (EY) tells you what percentage of the soluble material in your ground coffee made it into the liquid. The SCA target range is 18% to 22%.

How Does the Atago Refractometer Work?

Atago measures the concentration of dissolved solids in your coffee — called TDS (Total Dissolved Solids) — through light refraction. You place a few drops on the prism; as light passes through, the dissolved compounds bend it. The device converts that bend into a percentage.

TDS alone doesn't give you the full picture. For extraction yield, you need this formula:

EY (%) = [ TDS (%) × Brewed Coffee (g) ] ÷ Ground Coffee (g)

Three numbers: the TDS from Atago, the weight of liquid in your cup, and the weight of ground coffee you started with. That's all it takes. 

Step by Step: Calculating Extraction Yield with Atago

1. Weigh everything. Record your dry dose (g) and the brewed liquid you produced (g). A reliable coffee scale is non-negotiable.

2. Let it cool slightly. Very hot liquid can skew the reading. A couple of minutes, or a single cooler drop, is enough. Using a barista-grade thermometer can be very useful in this process.

3. Calibrate and measure. Zero with distilled water, then spread 2–3 drops of coffee evenly across the prism.

4. Read the TDS. For the sake of this example, we will be using 1.35%.

5. Run the formula. EY = (1.35 × 200g) ÷ 15g = 18.0% — you're at SCA's lower boundary. A finer grind or longer brew time will push you toward 20%.

How to Use These Numbers in Practice

Different brewing methods naturally produce different concentrations, so TDS should always be read in context. The table below gives you a practical reference point for several common brew methods, showing the typical TDS range, extraction yield and brew ratio for each. Make sure to use these numbers as a starting point rather than a strict rule. If your coffee tastes unbalanced, they can help you identify which part of the recipe may need adjusting.

Brew Method

Target TDS (%)

Target EY (%)

Typical Ratio

Filter / Pour Over

1.15 – 1.45

18 – 22

1:15 – 1:17

Espresso

8 – 12

18 – 22

1:2 – 1:2.5

French Press

1.2 – 1.5

18 – 22

1:14 – 1:16

Cold Brew (concentrate)

1.3 – 1.7

18 – 22

1:8 – 1:10

What Sets Atago Apart?

Most refractometers are calibrated for sugar solutions, not coffee. Atago's coffee-specific models — the PAL-COFFEE BX/TDS and PAL-COFFEE TDS — are adjusted for coffee's actual optical properties. Built-in Automatic Temperature Compensation (ATC) means you don't need to wait for your sample to fully cool. One drop is enough, it's easy to clean, and it fits in a pocket. Beyond convenience, the readings are consistent. If you hit 20% today with a given recipe, the same parameters should give you the same result tomorrow. In a professional setting that matters for quality control. At home it accelerates learning; you stop guessing and start adjusting.

Good Coffee Is About Understanding Your Brew

A refractometer gives you something taste alone cannot: a number you can compare from one cup to the next. But extraction yield is about more than just chasing a perfect percentage; it is about understanding why a coffee tastes the way it does, and knowing what to change when it does not taste quite right. Grind size, water temperature, brew time, coffee-to-water ratio and the coffee itself all affect your final cup. Tools such as the Atago refractometer simply make those relationships easier to see.

Whether you measure every brew or rely mostly on taste, learning the principles behind extraction gives you more control, and makes it much easier to recreate the cups you actually enjoy. Ready to experiment with your own brew? Explore our coffee beans and brewing equipment, or visit The Unusual Space and let our baristas make you a cup.

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