TDS (Total Dissolved Solids) In Coffee, Why Baristas Measure It

Walk into any specialty coffee bar and you’ll see gadgets on the counter that look more at home in a chemistry lab than a café.

One of them is a refractometer. It’s there for a reason: baristas measure TDS, or Total Dissolved Solids, in coffee to make sure what ends up in your cup isn’t guesswork.

TDS is the percentage of dissolved coffee solids in your brew. In simple terms: how much coffee is actually in your coffee, not counting the water. And yes, it makes a big difference.

TL;DR

TDS measures the percentage of coffee solids in your cup. Baristas track it to control extraction, balance flavor, and keep results consistent. For most brews, 1.15 -1.35% works for filter, 8 -12% for espresso. Go outside those ranges and the difference is obvious.

 

What TDS Actually Measures

 

TDS is expressed as a percentage. If your filter coffee has a TDS of 1.25%, that means 1.25% of your cup’s weight is coffee solids; the rest is water.

It’s not about whether your coffee is “strong” in the casual sense.

You can have a high-TDS coffee that still tastes thin if it’s over-extracted, or a low-TDS coffee that tastes intense because the flavors are concentrated but balanced.

A refractometer measures how light bends through your brewed coffee. The more solids in the liquid, the more the light bends. That reading gets converted to a TDS percentage.

 

Why Baristas Care About TDS

 

Consistency Between Cups

 

Without a metric, you’re relying on taste memory, which changes day to day. TDS gives a repeatable number. If yesterday’s filter coffee tasted perfect at 1.30%, you can aim for the same tomorrow.

 

Diagnosing Taste Problems

 

TDS works hand in hand with extraction yield.

Too low a TDS usually means under-extraction, you’ll get a weak body, possibly sour flavors. Too high a TDS often points to over-extraction, think bitterness and dryness.

This is the same territory where questions about dealing with sour-tasting coffee come in. TDS doesn’t tell you why something tastes off, but it helps you confirm if the brew strength is part of the problem.

 

Matching the Brew Method’s Range

 

Different brew methods have different ideal TDS ranges:

If your espresso comes out at 6% TDS, something went wrong, grind size, dose, or yield.

 

The Link Between TDS And Extraction Yield

 

Measuring TDS isn’t just about getting a number. When combined with the beverage weight and dose, you can calculate extraction yield, the percentage of the coffee grounds that actually dissolved into your cup.

Example:

- Dose: 18g coffee

- Yield: 36g espresso

- TDS: 10%

Extraction yield = (36 × 10%) ÷ 18 = 20%
That’s right in the SCA’s “ideal” range of 18–22%.

Why does this matter? Because a high TDS with a low extraction yield can taste overpowering yet flat, while a low TDS with high extraction yield can be watery but still bitter.

Most brewers aim for a balanced cup that falls within the Golden Cup range of about 1.15–1.35% TDS, or roughly 11.5–13.5 grams of dissolved solids per liter.

 

TDS In The Real World

 

Outside of competitions and training labs, most coffee drinkers never measure TDS. And that’s fine, unless you’re chasing precision.

For us as roasters, TDS readings are part of quality control. We know how our beans behave at different brew strengths.

If we change a roast profile, we check how it affects extraction. That’s how we make sure your coffee doesn’t suddenly shift from balanced to harsh.

For a home barista, TDS is a tool, not a rule. If you have a refractometer, use it to learn your preferred brew strength. Then use your palate first, numbers second.

 

Why TDS Isn’t Everything

TDS is just one metric. It won’t tell you:

- If the coffee is fresh or stale

- Whether the flavors are pleasant

- If your water quality is good

You can hit the perfect TDS and still end up with a terrible cup if the beans are old or poorly roasted. This is where freshness and roast-to-order coffee matter more than lab numbers. Old supermarket coffee with the “right” TDS still tastes like cardboard.

For a practical example, take a look at ways to deal with bitter-tasting coffee. Brew strength alone won’t fix fundamental quality issues.

 

Water Quality’s Role in TDS

 

Water is 98–99% of your coffee, so it has a massive influence on both TDS readings and taste. Hard water can lead to higher TDS readings because of minerals, but those minerals might block proper extraction. Soft water might brew cleaner but pull fewer solids from the coffee.

This is where TDS can be misleading: a refractometer measures total dissolved solids, not just coffee solids. If your water has a high mineral content before brewing, your baseline TDS is already elevated.

 

Should You Measure TDS At Home?

 

If you’re into data and want to dial in your brewing with precision, yes. A refractometer isn’t cheap, but it’s the fastest way to connect taste to measurable changes.

If you’re more interested in the ritual and the cup in front of you, you can still improve without it. Adjust grind size, ratio, and time until you get a flavor you enjoy. For deeper dives into method tweaks, you might find How does coffee grinding affect the taste? a good next step.

 

Freshness: The Missing Variable In TDS Measurements

 

This is where a lot of home brewers miss the point. You can spend hours chasing the “perfect” TDS, but if your beans were roasted months ago, the readings mean very little. Freshly roasted beans extract differently because the CO₂ from roasting is still present. This affects how water interacts with the grounds, and ultimately how much dissolves into your cup.

Once coffee stales, the cell structure changes, degassing stops, and water extracts flavor in a flatter, less complex way, even if the TDS number looks “right.” Measuring TDS without factoring in roast date is like judging wine quality only by its alcohol percentage. Numbers matter, but context matters more.

 

Final Thoughts

 

TDS in coffee isn’t about chasing numbers for the sake of it. It’s about control. Baristas measure it because they don’t want to guess, they want to know.

But TDS is only valuable if you pair it with taste and good coffee to start with. If your beans aren’t fresh or your roast profile is off, no refractometer will save you.

Measure if you want, taste always, and remember: the goal isn’t the reading on the meter, it’s the cup in your hand.