Extraction Diagnostic
Tell us what you taste. We’ll tell you what went wrong — and exactly how to fix it for your brew method.
EY% × TDS × SCA
Your coffee is in the sweet spot. The balance of organic acids, sugars, Maillard products, and controlled bitter compounds creates complexity and sweetness. This is the 18–22% extraction yield range where flavor quality peaks.
Extraction Yield vs. Strength: The Two Axes of Coffee Quality
The extraction diagnostic treats coffee troubleshooting as a two-dimensional problem rather than the one-dimensional approach most guides use. The two axes — extraction yield (EY%) and strength (TDS%) — are independent variables that require different fixes, and misdiagnosing which one is off leads to adjustments that make the cup worse.
Extraction yield measures what percentage of the coffee’s dry mass was dissolved into the liquid. It determines the flavor balance along the sour-to-bitter spectrum. The SCA’s 18–22% target reflects the chemistry of sequential dissolution: organic acids dissolve first (they’re small, polar molecules), then sugars and Maillard products, then the heavy bitter compounds — chlorogenic acid lactones and phenylindanes. Below 18%, acid compounds dominate and the cup tastes sour or underdeveloped. Above 22%, bitter compounds accumulate faster than pleasant complexity increases.
Strength, measured as TDS%, is about concentration, not balance. It determines body — how thin or heavy the cup feels. You can have a perfectly balanced extraction that’s too dilute (right EY, low TDS) or a concentrated cup that’s badly extracted (high TDS, wrong EY). This is why the diagnostic uses two separate inputs: one for flavor balance and one for body. Each combination maps to a specific adjustment strategy.
Brewing method changes the fix significantly. Grinding finer is the most impactful extraction lever for pour over because it increases surface area and slows flow through the coffee bed, giving water more contact time with the grounds. For espresso, the same adjustment has amplified effects because fine particles interact with 9 bars of pump pressure, and the relationship between grind size and puck resistance follows Darcy’s law — flow rate through the coffee bed depends on permeability, which changes dramatically with small particle size adjustments. Grinding one click finer in espresso can add 5–10 seconds to shot time, while the same change in pour over might add 15–30 seconds. For French press, grind adjustments affect extraction less than steep time because there’s no flow rate to modify — the coffee sits in a fixed volume of water approaching equilibrium.
Water temperature offers a complementary adjustment that operates through a different mechanism. Higher temperatures increase the diffusion coefficient of soluble compounds, accelerating extraction. But the same extraction yield achieved at different temperatures can taste different because temperature-dependent solubility means different compounds extract at different rates. A cup at 20% EY brewed at 96 degrees Celsius will have a slightly different flavor balance than one at 20% EY brewed at 90 degrees — the hotter brew extracts proportionally more of the heavier compounds. This is why the diagnostic accounts for method-specific temperature ranges alongside grind recommendations.
How This Works
The Extraction Curve
Coffee extraction is sequential. Organic acids dissolve first (they’re small, polar molecules), followed by sugars and Maillard reaction products, then finally the heavier bitter compounds — CGA lactones and phenylindanes. Every cup is a snapshot of how far along this dissolving curve you went. Too little extraction: sour and underdeveloped. Too much: harsh and bitter. The sweet spot lives in the middle.
Acids → Sugars → Bitters
The three stages aren’t equal in volume. Acids make up roughly 10–15% of soluble mass but dissolve earliest and fastest. Sugars and Maillard products represent the bulk of pleasant flavor (40–50%) and come next. Bitter compounds dissolve last — they’re large, complex molecules that need more energy (time, heat, surface area) to extract. The goal is to dissolve enough sugars to balance the acids without pulling significant bitters.
The SCA 18–22% Standard
The Specialty Coffee Association established the 18–22% extraction yield range through decades of sensory research. At this range, trained tasters consistently rate coffee highest for flavor quality. Below 18%, acid compounds dominate and the cup tastes sour or underdeveloped. Above 22%, bitter compounds accumulate faster than flavor complexity increases. The “Gold Cup” standard pairs this with 1.15–1.35% TDS for filter coffee.
Strength vs. Extraction
These are independent variables, which is why this tool uses two sliders. Extraction Yield (EY%) measures what percentage of the coffee’s mass was dissolved — it determines flavor balance (sour vs. bitter). Total Dissolved Solids (TDS%) measures the concentration of those dissolved compounds in your cup — it determines body (thin vs. heavy). You can have high extraction at low strength (bitter and watery) or low extraction at high strength (sour and intense). Fixing your coffee requires identifying which axis is off.
SCA Brewing Standards (2019). Lockhart, E.E. "The Soluble Solids in Beverage Coffee as an Index to Cup Quality" (Coffee Brewing Institute, 1957). Rao, S. "Everything But Espresso" (2010). Hendon, C. et al. "The Role of Dissolved Cations in Coffee Extraction" (Journal of Agricultural and Food Chemistry, 2014). Specialty Coffee Association of America. "Gold Cup" Brewing Standard.