TDS, Extraction, and Roast Color: How Asante Measures a Good Cup

Specialty coffee is often described in the language of romance—terroir, craft, passion. All of that is real, but underneath it is something less often spoken about: measurement. The difference between coffee that is consistently excellent, and coffee that is only occasionally good, almost always comes down to a discipline of measurement. At Asante, quality control hinges on two pillars: roast colour and total dissolved solids (TDS). Here’s what those terms mean, and why they matter for what ends up in your cup.

Concentration vs. extraction: two different things

People often use “strong” vaguely, but in coffee, concentration and extraction are distinct, measurable properties.

·     Concentration (TDS) is how strong the brew is—the percentage of the liquid that is dissolved coffee rather than water. It’s measured as total dissolved solids, or TDS, usually with a refractometer.

·     Extraction yield is how much of the available coffee mass has actually dissolved into the brew, expressed as a percentage of the dry coffee used.

A coffee can be concentrated but underextracted (strong, but sour and undeveloped), or weak but overextracted (watery, but bitter). Brewing well means controlling both at once.

The SCA’s extraction control chart

The SCA’s extraction control chart plots these two properties to define a target zone for balanced filter coffee.

·     Ideal extraction yield: around 18–22%. Below this, coffee tends to taste sour, salty, and undeveloped. Above it, it tends to taste bitter, dry, and astringent.

·     Ideal concentration (TDS): around 1.15–1.35% for filter coffee, in the classic “Gold Cup” range, though preferences vary by region and by palate.

At the point where extraction and concentration meet within this zone, coffee tastes balanced and sweet. The chart turns subjective tasting into something you can target and reproduce.

Property	What it measures	Typical filter target	If too low	If too high
Concentration (TDS)	Brew strength	~ 1.15–1.35%	Watery, thin-bodied	Heavy, overwhelming
Extraction yield	% of coffee dissolved	~ 18–22%	Sour, salty	Bitter, dry

 

Where the refractometer comes in

A refractometer measures how light bends as it passes through brewed coffee, which corresponds to the TDS. From the TDS reading, the brew ratio, and the weight of coffee used, you can then calculate the extraction yield. This allows a roaster or barista to answer a precise question—“did this brew fall into the balanced zone?”—rather than guess. It’s the bridge between a recipe and a repeatable outcome.

The practical benefit for you at home is simpler than the instrument suggests: the brewing recommendations we give for our coffees are built on these measurements, so following them gets you closer to the balanced zone without needing the equipment.

Roast colour: measuring development, not just darkness

The second pillar is roast colour. Colour is an indicator of how far roast development has progressed—the chemical reactions, primarily Maillard reactions and caramelisation, that build flavour as the bean roasts. Measuring colour (with colour disks or a dedicated meter) gives an objective check on roast development that the eye alone can’t reliably judge under varying light.

Crucially: we measure the colour of both the whole bean and the ground. A difference between the two—a darker interior than exterior, or vice versa—reveals uneven development inside the bean, often pointing to roasting mechanics like drum speed, airflow, or batch size. Roast colour is therefore not just a final check, but a diagnostic that feeds back into how we roast the next batch.

Why measurement is a form of respect

It would be easy to treat measurement as something cold or clinical, the opposite of craft. We see the opposite. We start with green coffee selected at 84+ on the SCA scale and sourced from producers who have done painstaking work at origin. Measuring roast colour and TDS is how we honour that work—how we ensure the potential of the green bean is consistently realised, bag after bag, rather than left to chance. Precision is not at odds with passion; it’s how passion becomes reliable.

Frequently asked questions

What is TDS in coffee?

TDS stands for total dissolved solids—the percentage of a brewed coffee that is dissolved coffee material rather than water. It’s a measure of concentration, usually read with a refractometer and expressed as a percentage.

What is the ideal extraction percentage for filter coffee?

The SCA extraction control chart points to an extraction yield of around 18–22%. Below that range, coffee tends to taste sour and undeveloped; above it, bitter and astringent.

What’s the difference between concentration and extraction?

Concentration (TDS) is how strong the brew is; extraction yield is how much of the coffee mass has dissolved into the brew. They are independent—a coffee can be concentrated but underextracted, or weak but overextracted.

Why do roasters measure roast colour?

Roast colour is an objective indicator of how far flavour development has progressed during roasting. Measuring both whole bean and ground colour also reveals whether a bean has developed evenly inside and out, which helps diagnose and refine roasting decisions.

Asante’s perspective

Knowledge and transparency are values we live by, and this is what they mean behind the counter: instruments, targets, and honest feedback loops in service of flavour. When you brew one of our coffees, you’re tasting the end of a measured process that started with a hand-selected green bean. We invest in the art—and the measurement—so you can taste the perfect result.