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The Control Chart — Extraction Yield Diagnostic

Coffee Science · No. 03

The Control Chart

Extraction Yield and TDS are independent measurements — a coffee can be weak and perfectly extracted, or strong and badly extracted. This plots your actual numbers against the standard brew control chart, and — the part most calculators skip — flags when the average looks fine but the bed almost certainly wasn't extracting evenly.

Under-extracted — low EY
Over-extracted — high EY
In zone, but channeling likely
01

Method & measurements

Weigh the brewed beverage directly rather than back-calculating from water poured in — grounds retain a variable amount of water.

Leave at 1.00 unless your meter's manual specifies otherwise.

How this is calculated
EY% = (TDS% × corrected beverage mass) ÷ dose × 100. Filter/immersion ideal zone: EY 18–22%, TDS 1.15–1.35%. Espresso ideal zone: EY 18–22%, TDS 8–12% — same extraction target, much higher concentration because so much less water is used per gram of coffee.
02

What does it taste like?

This is what catches channeling — a good number with contradictory taste notes is the tell.

Sour / thin cluster
Bitter / astringent cluster
Flat / muted cluster

Reading

Live, updates as you type

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Extraction yield
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Strength (TDS)
Enter your numbers
Fill in dose, beverage mass and TDS to plot your point.
A refractometer reading is a bed average. If the diagnosis below says "in zone" but the cup still tastes off, trust the taste notes — uneven extraction can read as ideal on average while tasting wrong in the cup.
03

What you'll need to measure this

This tool is only as good as the TDS reading you feed it — the refractometer is the one piece of gear worth researching before you buy. Replace the placeholder links with your own affiliate links before publishing.

Budget pick
DiFluid R2 Extract
Around $200 vs. $700+ for the VST, and in independent comparative testing it matches the VST closely on accuracy while running slightly lower on absolute readings — the app-based shot logging is a genuine convenience the pricier models don't have.
View option →
Lab-grade reference
VST LAB Coffee III
The instrument the specialty coffee industry benchmarks everything else against — tightest run-to-run consistency of any model, at a $700–$1,400 price point. Worth it if you're publishing extraction data others will scrutinize, overkill for casual dialing-in.
View option →
Alternative
Atago PAL-Coffee
Reads both TDS and Brix from a well-regarded Japanese manufacturer, priced near the VST — but independent testing shows it needs more frequent recalibration than the VST, so it's a harder recommendation than it used to be now that DiFluid exists at a third of the cost.
View option →
For weighing beverage mass
0.1 g precision digital scale
EY calculations amplify small weighing errors, since dose and beverage mass both feed directly into the formula — a scale that rounds to a full gram introduces more error into your EY% than most grind adjustments correct for.
View option →

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Change one variable at a time — grind first, then time/agitation, then temperature. Ratio is a strength lever, not a taste-quality lever.