Percolate
Coffee extraction yield (EY) is the percentage of a coffee ground's soluble mass that actually dissolves into your cup. The Specialty Coffee Association's target is 18-22%. Too little extraction produces sour, thin coffee; too much produces bitterness. TDS -- total dissolved solids -- measures brew strength and is the number you need to calculate EY.
If you’ve ever brewed a coffee that smelled incredible but tasted sharp and hollow — or smooth on the nose but bitter on the finish — you’ve already experienced extraction working against you. Understanding extraction yield and its companion stat, TDS, is the single biggest step forward for home brewers who want to stop guessing and start diagnosing.
A question we hear often: what do all those percentages on brewing guides actually mean?
Extraction yield (often abbreviated EY) is the percentage of a coffee ground’s soluble mass that dissolves into your brewed cup. It represents the percentage of all soluble substances successfully extracted from the coffee beans during brewing. That percentage matters because not all of those solids taste good — the key to a good brew is to leave as much of the undesirable solids behind while taking out all the good stuff.
Only 30% of the coffee bean is soluble; the other 70% consists of insoluble fiber and carbohydrates, which are responsible for the structure of the bean. Of that soluble 30%, the sweet spot the industry has converged on is extracting roughly 18-22%. The chart’s origins go back to 1950s research by Ernest E. Lockhart at MIT, which produced the original Coffee Brewing Control Chart and established the 18-22% EY range as the “ideal extraction” window. The Specialty Coffee Association inherited and refined it — today it anchors their Golden Cup Standard.
Why does this matter at home? Because EY gives you a precise vocabulary for what your palate is already telling you. Instead of “something is off,” you can ask: am I under- or over-extracted, and which single variable should I change?
These two numbers describe different things, and mixing them up is the most common point of confusion.
TDS, or Total Dissolved Solids, is a measurement of how much “coffee” is dissolved in your cup — in simple terms, it tells you how strong your coffee is. Extraction yield, on the other hand, tells you how efficiently you extracted relative to your dose. Both values complement each other: TDS measures the strength, the extraction rate the efficiency of the solution.
Here’s the practical gap between them: two cups can share the same TDS reading and taste completely different. Two coffees can have the same TDS and taste completely different depending on how evenly and how deeply they were extracted. You can also hit a high TDS (strong coffee) while still under-extracting — for example, if you use a very high dose but a very short brew time.
| Metric | What it measures | Unit | Typical range |
|---|---|---|---|
| TDS (filter) | Brew strength / concentration | % | 1.15-1.45% |
| TDS (espresso) | Brew strength / concentration | % | 8-12% |
| Extraction Yield | % of grounds dissolved | % | 18-22% (target) |
| SCA brewing water TDS | Mineral content of input water | mg/L (ppm) | 75-250 mg/L |
Note that “TDS” refers to two completely different measurements depending on context: the dissolved solids in your finished cup (a strength indicator) versus the mineral content of your brewing water (a water quality indicator). The SCA specifies a TDS level of 75-250 mg/L (ppm) for brewing water, with an ideal target of 150 mg/L. That’s a different measurement than the 1.2-1.5% TDS of your brewed filter coffee.
This one comes up a lot: do I really need a refractometer, or can I figure this out without spending $200?
TDS is measured using a refractometer — a device that works by passing light through a liquid and measuring how much that light bends. The more dissolved material in the liquid, the more the light refracts. Once you have a TDS reading, the extraction yield formula is straightforward:
EY (%) = Beverage weight (g) x TDS (%) / Dose (g)
For example: if you brewed 300 g of filter coffee from an 18 g dose and your refractometer reads 1.35% TDS, your extraction yield is roughly (300 x 1.35%) / 18 = 22.5% — right at the top of the SCA target window.
Refractometers are not commonly used, even in coffee shops, let alone in home brewing. If you don’t have one, don’t panic. The first thing to focus on is the correct coffee-to-water ratio, which will help you achieve a proper TDS. From there, you can rely on taste and adjust the recipe according to the outcome. Your palate is a genuinely useful instrument — more on that below.
Extraction isn’t random. Water pulls compounds from coffee grounds in a predictable order: acids and simple sugars come first, then more complex sugars and body-building compounds, and bitter or astringent compounds come last. If extraction stops too early, you get mostly acid — with no sweetness or body to balance it. That’s why under-extracted coffee often tastes sour, thin, or even salty.
The sour/salty combination is the clearest tell. If you taste a coffee and the first things that come to mind are that it’s overwhelmingly sour and there’s no sweetness to temper it, you’ve likely got an under-extracted coffee on your hands. The fix usually comes down to one thing: grind finer. That said, brewing hotter or extending contact time both give water more opportunity to reach deeper into the grounds and pull out balancing sweetness.
Among these variables, grind size is usually the most effective to adjust because it directly controls extraction speed. Finer grinding increases surface area dramatically, giving water more to work with.
Readers frequently ask: my coffee isn’t sour, it’s just… harsh and dry. Is that the same problem?
No — that’s the opposite problem. Over-extraction happens when you extract too much, including the bitter, woody, or dry-tasting compounds that appear late in the brewing process. Where under-extracted coffee finishes abruptly with a sharp edge, over-extracted coffee tends to linger unpleasantly — a dry, rough mouthfeel that overpowers any origin character.
Several different factors can lead to over-extraction: too fine a grind, too much water, or too long a contact time. The mirror-image fix applies: grind coarser, brew slightly cooler, or shorten contact time. The key discipline is changing one variable at a time — adjusting two things simultaneously makes it impossible to know which change actually worked.
It’s worth noting that the 18-22% window is a guideline, not a ceiling. It’s quite possible for a coffee to be well over 22% extraction and taste not only good, but spectacular. High-quality beans contain fewer undesirable compounds, meaning even if you extract slightly above 22%, the cup can still taste great. This is one reason logging the beans you brew — their origin, process, and roast level — helps you calibrate your expectations. Percolate’s cupping-note shelf is built for exactly this: when you log a bag and its brew notes, patterns emerge across sessions that let you predict how a new coffee will behave before you’ve dialed it in.
TDS can give roasters, baristas, and coffee lovers a valuable insight into the solubility of a roast: the darker the roast, the more solubles in the bean are present, and the lighter the roast, the less solubles are present. In practice, dark roasts extract faster and can reach the 18-22% window more easily with a coarser grind or lower temperature. Light roasts are denser and often need a finer grind, higher temperature, or longer steep to extract fully.
With this in mind, you might do shorter extractions with a finer grind for a dark roast and longer extractions with a medium-coarse grind for a lighter roast. If you’re brewing a light Ethiopian natural that tastes persistently sour despite a “correct” recipe, the bean’s density — not your technique — may be the bottleneck. Try grinding two steps finer before changing anything else. (For a deeper look at how roast levels affect solubility and flavor, see our coffee roast levels guide.)
A question we hear often: I hit 1.35% TDS every time — so why does my coffee still taste mediocre?
Because TDS measures how much dissolved material is in the cup, not which compounds or whether they taste pleasant. TDS doesn’t comment much on the quality of coffee because it only measures total dissolved solubles and not what those solubles are — it says nothing about which of the 100+ compounds in coffee beans have been extracted.
If a brew is unevenly extracted, where parts of the coffee bed are under-extracted and other parts over-extracted, the overall extraction might in fact be within the acceptable range — yet the cup will taste muddled and unpleasant. Even channeling (water finding preferential paths through the grounds) can produce a technically “good” TDS reading while delivering a cup that’s simultaneously sour and bitter.
TDS and extraction percentage are not targets to chase blindly — they’re diagnostic tools, reference points that help explain why a coffee tastes the way it does. The sensory check always comes last: measure, then taste, then decide.
Use this when a brew isn’t hitting right:
| Symptom | Likely cause | First fix |
|---|---|---|
| Sour, sharp, no sweetness | Under-extraction | Grind finer |
| Salty, thin, quick finish | Under-extraction | Increase water temperature |
| Bitter, dry, hollow | Over-extraction | Grind coarser |
| Harsh, astringent, long bad finish | Over-extraction | Shorten contact time |
| Flat, no origin character | Low TDS / weak brew | Increase dose or grind finer |
| Muddled, sour AND bitter | Uneven extraction | Improve distribution / stir grounds |
Change one variable per session, taste, log the result, repeat. The fastest route to a dialed-in recipe is a short feedback loop — which is exactly the workflow Percolate’s structured cupping-note format is designed to support. Log your TDS estimate, your taste impressions, and your next-session adjustment in a single entry, and the pattern becomes obvious within three or four brews.
For context on how grind size interacts with all of this, see our coffee grind size guide. And if your brew water’s mineral TDS is outside the SCA’s 75-250 ppm window, even a perfect extraction yield won’t produce a great cup — our brew water temperature guide covers the water chemistry angle in detail.
What is TDS in coffee?
TDS stands for Total Dissolved Solids -- the percentage of your brewed coffee that is dissolved coffee material rather than water. A typical filter coffee lands between 1.15% and 1.45% TDS. It measures strength (concentration), not quality or extraction efficiency on its own.
What is a good extraction yield for coffee?
The Specialty Coffee Association's Golden Cup Standard defines the ideal extraction yield as 18-22% for filter coffee. That means 18-22% of the dry coffee grounds' mass has dissolved into your cup. Below 18% is generally under-extracted; above 22% risks over-extraction, though high-quality beans can taste great beyond this range.
How do I calculate coffee extraction yield without a refractometer?
Without a refractometer you can use taste as your primary guide: sour and thin means under-extracted, dry and bitter means over-extracted. Some brewers estimate EY by cross-referencing their coffee-to-water ratio against known TDS ranges for their brew method, but the result is approximate. A precise calculation requires a refractometer reading.
What does under-extracted coffee taste like?
Under-extracted coffee tastes sour, sharp, and sometimes salty, with little sweetness and a quick, unsatisfying finish. This happens when too little of the bean's soluble material has dissolved -- acids are pulled first, but sugars and other balancing compounds haven't had time to follow.
What does over-extracted coffee taste like?
Over-extracted coffee tastes bitter, dry, or hollow -- sometimes described as woody or harsh. These unpleasant compounds are the last things water pulls from the grounds, so they only appear when brewing goes too long, the grind is too fine, or water is too hot.
Does roast level affect extraction yield?
Yes. Darker roasts are more porous and soluble, so they extract faster and more completely at a given grind size and temperature. Lighter roasts are denser and require a finer grind, higher water temperature, or longer contact time to reach the same extraction percentage.