TDS and Extraction in Fine Robusta: What the Numbers Actually Mean

TDS tells you how concentrated the beverage is. Extraction yield estimates how much soluble material was removed from the dry coffee. Neither number tells you, by itself, whether a Fine Robusta tastes good.

That distinction matters because coffee brewing advice often turns TDS and extraction into a pass/fail score. A cup at one percentage is called “ideal,” while another is called automatically weak, bitter, under-extracted, or over-extracted. Modern sensory research does not support such a simple map.

For Fine Robusta, the more useful role of TDS and extraction is descriptive: they help a brewer reproduce a beverage, compare recipes, separate concentration from extraction, and understand what changed when the cup changes.

What is TDS in coffee?

TDS means total dissolved solids. In brewing practice, it is the mass fraction of dissolved coffee material in the beverage, usually reported as a percentage.

If a filtered coffee reads 1.35% TDS, approximately 1.35% of the beverage mass is measured as dissolved coffee solids under the instrument’s calibration model. Espresso values are much higher because the beverage contains much less water relative to coffee dose.

TDS is therefore mainly a measurement of strength or concentration.

It is not the same as caffeine concentration, bitterness, body, or quality.

A 1.50% filter brew can taste excellent or unpleasant. A lower-TDS brew can be highly extracted but dilute. A high-TDS espresso can be well balanced or harsh depending on roast, flow, yield, water, and the coffee itself.

What is extraction yield?

Extraction yield, often abbreviated EY or PE for percent extraction, estimates the fraction of the original dry coffee mass that ended up dissolved in the beverage.

The classic calculation uses beverage mass, TDS, and dry coffee dose. In simplified form:

Extraction yield ≈ beverage mass × TDS ÷ dry coffee dose.

The exact calculation becomes more complicated when retained liquid, bypass water, measurement technique, or immersion brewing are considered.

Extraction yield answers a different question from TDS.

TDS asks: How concentrated is the drink?

Extraction asks: How much soluble material did we remove from the grounds?

Those two questions should not be collapsed.

Why can a coffee be strong but under-extracted?

Use a lot of coffee and too little water, and the beverage can become concentrated even if extraction from each gram of coffee is incomplete.

Imagine a short brew with a high dose, coarse grind, and very limited water. Its TDS may be high because the beverage is concentrated, but its extraction yield may remain relatively low.

Sensory results can include intense but hollow flavor: strong concentration without complete development.

This is especially relevant to espresso and moka pot, where beverage concentration is naturally high.

A strong Fine Robusta is not necessarily an over-extracted Fine Robusta.

Why can a coffee be weak but highly extracted?

Use a relatively dilute coffee-to-water ratio and give the water enough time and access to the grounds, and the final beverage can have low TDS but comparatively high extraction yield.

The cup may taste clean but simply too dilute for the drinker.

In that situation, grinding finer may be the wrong correction. The extraction may already be adequate. A stronger brew ratio may solve the actual problem.

This is why OCC separates strength problems from extraction problems before changing grind or temperature.

Where did the classic brewing chart come from?

The modern coffee industry inherited much of its language from the Coffee Brewing Institute work of the 1950s, especially Ernest Lockhart’s brewing-control framework. The chart related beverage strength, extraction yield, and brew ratio and identified a central region historically described as desirable.

That chart became extremely influential.

Its strength is practical: it gives brewers a common measurement language.

Its weakness is what happened later. The central region was often treated as if it were a universal law of sensory quality across coffees, roasts, consumers, and brew styles.

Modern research at the UC Davis Coffee Center has tested those assumptions more rigorously.

What changed in the 2023 Brewing Control Chart research?

Guinard and colleagues published a new Coffee Brewing Control Chart in 2023 based on a series of controlled sensory and consumer studies.

Their work found that sensory attributes change across the TDS/extraction space in more complex ways than the old labels suggest. Consumer liking also did not collapse into one universal “ideal” point. Instead, different preference clusters favored different parts of the brewing space.

That is a major correction to the internet version of the chart.

The chart remains useful for navigation.

It should not be treated as a universal quality tribunal.

Does the 18–22% extraction range define good Fine Robusta?

No.

The familiar approximately 18–22% range comes from the historical brewing-control tradition. It can still be a useful reference zone for many filtered coffees, but there is no peer-reviewed evidence establishing it as the sensory optimum for all Coffea canephora, all roasts, or all brewing methods.

Fine Robusta has no scientifically validated species-specific extraction percentage.

The correct use is:

• measure the brew;
• taste the brew;
• identify a desirable result;
• use TDS and extraction to reproduce or intentionally move away from it.

Do not reverse the logic and declare a cup good because the calculator returned a favored number.

What did the strength-and-extraction sensory study find?

Frost, Ristenpart, and Guinard systematically varied TDS and extraction yield in drip-brewed coffee across three roast levels.

Their trained panel found that many sensory attributes changed significantly with TDS, extraction, and roast. The relationships were not captured by a simple “low extraction = sour, high extraction = bitter” rule.

Important limitation: the experimental coffee was Arabica, not Canephora.

OCC therefore uses the study as brewing-science evidence about the relationship among physical brew metrics and sensory perception, not as a direct Fine Robusta optimum.

The lesson still matters: roast and strength can change sensory interpretation of extraction.

What does consumer research say?

Cotter and colleagues tested consumer preference across a wide range of strength and extraction conditions.

Consumers did not agree on one narrow optimum. Preference was distributed, with different groups liking different brew strengths and extraction yields.

That means a café’s target should depend partly on the beverage style and customer, not only on a historical chart.

For Fine Robusta, this is particularly relevant because some drinkers may value dense body and bitterness while others prefer clarity and lower concentration.

There is no reason to assume one species should have one consumer target.

Does temperature determine extraction quality?

Temperature changes extraction kinetics, but temperature alone does not determine sensory quality.

Batali, Ristenpart, and Guinard brewed drip coffee at 87°C, 90°C, and 93°C while adjusting grind and time so the final TDS and extraction were comparable. When strength and extraction were matched, sensory profiles were much more similar than commonly assumed.

Again, the coffee was washed Arabica.

For Fine Robusta, the systems lesson is useful: temperature is one way to reach an extraction condition. It is not an isolated quality score.

Direct Robusta temperature studies also show method-specific effects, reinforcing that one fixed temperature or extraction number should not be generalized across all Canephora.

How does grind affect the numbers?

Finer grinding usually increases available surface area and extraction rate, but percolation introduces flow resistance.

Espresso research by Cameron and colleagues demonstrated a crucial nonlinear effect: grinding progressively finer eventually produced lower extraction yield because flow through the puck became increasingly inhomogeneous.

Smrke and colleagues later showed that the fines fraction can strongly reduce coffee-bed permeability and alter flow and extraction time.

So if a Fine Robusta espresso shows lower extraction than expected, “grind finer” is not always the correct answer.

The puck may already be too restrictive.

Why is immersion different?

In full-immersion methods, grounds and water remain in contact without continuous percolation through a compact bed.

Liang, Chan, and Ristenpart developed an equilibrium desorption model showing that brew strength and extraction behave differently from simple percolation assumptions. Their work helps explain why extraction approaches an equilibrium and why brew ratio strongly affects TDS while extraction yield can behave differently.

This matters for French press and cupping-style systems.

A TDS/extraction equation copied from drip coffee should not be applied mechanically without understanding retained liquid and the brewing model.

Does a refractometer measure every solid perfectly?

No measurement is perfect.

Coffee refractometers estimate TDS through refractive index and a coffee-specific calibration. The sample must be representative, well mixed, and within the instrument’s operating method. Temperature compensation, suspended particles, oils, crema, evaporation, and sample handling can affect readings.

Espresso is especially challenging because crema and suspended solids can make the sample heterogeneous.

For repeatable QC:

• stir the beverage consistently;
• allow foam/crema handling to follow one protocol;
• use the same instrument;
• clean and calibrate it;
• record beverage mass accurately; and
• do not compare measurements taken under different procedures as if they were identical.

Precision without method consistency is false precision.

Is TDS the same as body?

No.

Higher TDS often increases perceived intensity and can contribute to thickness, but sensory body also includes suspended solids, colloids, polysaccharides, lipids, phenolics, melanoidins, fines, filtration, and saliva interactions.

A paper-filtered coffee and a French press can have similar measured TDS but different tactile profiles.

Fine Robusta’s familiar body therefore cannot be reduced to one refractometer number.

Is extraction yield the same as bitterness?

No.

Bitterness comes from multiple chemical and sensory sources: caffeine, chlorogenic-acid lactones and other roast products, concentration, green defects, processing, and extraction distribution.

A darker roast can be bitter at modest extraction. A high-extraction light roast can be sweet and transparent. An uneven espresso can contain both highly extracted and poorly extracted regions in the same cup.

Use extraction yield as a physical metric, not a taste label.

A practical TDS workflow for Fine Robusta filter coffee

Start with a stable recipe, such as 15 g coffee to 240 g water.

Record:

1. coffee dose;
2. water input;
3. final beverage mass;
4. grind setting and grinder;
5. brew time;
6. temperature;
7. TDS; and
8. sensory notes.

Calculate extraction only after the physical data are reliable.

If a cup is excellent, those numbers become a reproduction target for that coffee and method.

If it is hollow, drying, muddy, or too concentrated, use the data to decide which variable to change.

A practical workflow for Fine Robusta espresso

For espresso, record dose, beverage yield, time, temperature, pressure/flow settings if available, grinder setting, and TDS.

Do not use extraction yield alone to judge a shot.

If the shot is slow and inconsistent, inspect distribution and grind before chasing a higher extraction number.

If the espresso is clean but too intense, extend beverage yield or dilute rather than assuming extraction is wrong.

If it is thin and undeveloped, check flow uniformity and grind.

The purpose of measurement is to diagnose the system, not reward a percentage.

What should OCC publish as a Fine Robusta target?

Not one universal number.

OCC can publish measured recipes when the underlying coffee, roast, grinder, brewer, water, and sensory result are documented. Those recipes become useful lot-level evidence.

For example: “This medium-roasted lot tasted best to our panel at X TDS and Y estimated extraction under this brewer and water.”

That is evidence.

“Fine Robusta should always be 1.45% TDS and 20% extraction” would not be.

Frequently asked questions

What TDS is ideal for Fine Robusta?

There is no universal Fine Robusta TDS. TDS is beverage concentration. Choose it for the brewing style and sensory target.

Is 18–22% extraction the Fine Robusta standard?

No. It is a historical reference zone from brewing-control practice, not a validated Canephora quality standard.

Does high TDS mean over-extracted?

No. High TDS means concentrated. Extraction yield must be calculated separately.

Can low-TDS coffee be highly extracted?

Yes. A dilute brew can extract a large fraction of soluble material while still tasting weak because the beverage contains more water.

Why did extraction fall when I ground espresso finer?

Very fine grinding can reduce permeability and create uneven flow. Espresso research has documented an extraction peak followed by lower extraction at excessively fine settings.

Does a refractometer tell me whether coffee tastes good?

No. It describes concentration. Sensory evaluation remains necessary.

The measurement rule that matters

TDS and extraction are most valuable when they describe a cup you have already evaluated.

TDS tells you strength. Extraction yield tells you how much material left the grounds. Sensory evaluation tells you whether that physical result is desirable.

Keep those three questions separate and Fine Robusta becomes easier to dial in, compare, and reproduce without turning a historical chart into a species stereotype.

Sources and technical references

• Guinard, J-X. et al. “A new Coffee Brewing Control Chart relating sensory properties and consumer liking to brew strength, extraction yield, and brew ratio.” _Journal of Food Science_ 88(5), 2168–2177 (2023). DOI: 10.1111/1750-3841.16531.
• Frost, S.C., Ristenpart, W.D. & Guinard, J-X. “Effects of brew strength, brew yield, and roast on the sensory quality of drip brewed coffee.” _Journal of Food Science_ 85(8), 2530–2543 (2020). DOI: 10.1111/1750-3841.15326.
• Cotter, A.R. et al. “Consumer preferences for black coffee are spread over a wide range of brew strengths and extraction yields.” _Journal of Food Science_ 86(1), 194–205 (2021). DOI: 10.1111/1750-3841.15561.
• Batali, M.E., Ristenpart, W.D. & Guinard, J-X. “Brew temperature, at fixed brew strength and extraction, has little impact on the sensory profile of drip brew coffee.” _Scientific Reports_ 10, 16450 (2020). DOI: 10.1038/s41598-020-73341-4. Arabica limitation retained.
• Liang, J., Chan, K.C. & Ristenpart, W.D. “An equilibrium desorption model for the strength and extraction yield of full immersion brewed coffee.” _Scientific Reports_ 11, 6904 (2021). DOI: 10.1038/s41598-021-85787-1.
• Cameron, M.I. et al. “Systematically Improving Espresso: Insights from Mathematical Modeling and Experiment.” _Matter_ 2(3), 631–648 (2020). DOI: 10.1016/j.matt.2019.12.019.
• Smrke, S., Eiermann, A. & Yeretzian, C. “The role of fines in espresso extraction dynamics.” _Scientific Reports_ 14, 5612 (2024).
• Specialty Coffee Association / UC Davis Coffee Center technical interpretation of modern Brewing Control Chart research. Used as brewing framework, not as a species-specific Fine Robusta standard.