You followed the recipe. 15 grams of coffee, 250 grams of water, medium grind, three-minute brew. It still tastes thin and sour — or harsh and drying. So what went wrong?
The answer almost always lives inside two numbers: TDS and extraction yield. Once you understand what they mean, every recipe online stops feeling like a magic spell.
TL;DR
TDS is how strong your coffee tastes. Extraction yield is how much you pulled out of the grounds. The sweet spot for pour-over is roughly 1.30–1.45% TDS and 18–22% extraction yield — and you can hit it by taste alone.
What TDS and Extraction Yield Actually Measure
TDS (Total Dissolved Solids) is the percentage of your brewed cup that is dissolved coffee instead of water. A TDS of 1.35% means 1.35 grams of every 100 grams in your mug are coffee solids. The rest is water.
Extraction yield (EY) is the percentage of the dry coffee grounds that ended up dissolved in your cup. If you brewed with 15 g of coffee and pulled 3 g of solids into the cup, that is a 20% extraction.
A real example: you brew 15 g of coffee with 250 g of water and end up with about 225 g of liquid in the server (the grounds keep the rest). If that liquid measures 1.35% TDS, you dissolved roughly 3.04 g of coffee — a 20.2% extraction yield. Right in the middle of the target.
How It Works: The Brewing Control Chart
The Specialty Coffee Association mapped these two numbers onto a grid called the brewing control chart. Decades of taste panels found the same window kept coming back as “balanced”:
- Under 18% EY — under-extracted. Sour, salty, sharp, vegetal.
- 18–22% EY — the sweet spot. Sweet, balanced, clear flavors.
- Over 22% EY — over-extracted. Bitter, drying, ashy, hollow finish.
TDS sets the thickness of that flavor. Below 1.15% it tastes watery; above 1.55% it tastes muddy. Pour-over lives best around 1.30–1.45%.
The two numbers are linked by your brew ratio (coffee-to-water). At a 1:16.7 ratio (15 g coffee to 250 g water), a 20% extraction lands near 1.35% TDS automatically. That is why almost every V60 recipe online uses a ratio between 1:15 and 1:17.
The Common Mistake: Confusing Strength With Extraction
Beginners taste a weak cup and add more coffee. That raises TDS (stronger) but does nothing to fix a sour, under-extracted brew. The grounds are still under-extracted — you just have more of them.
How to tell which problem you actually have:
- Sour or salty up front, fades fast? Under-extracted. Grind finer or brew longer.
- Bitter, drying, lingers unpleasantly? Over-extracted. Grind coarser or brew shorter.
- Tastes correct but watery? Strength issue. Use more coffee or less water.
- Tastes correct but heavy and muddy? Use less coffee or more water.
Extraction is about grind size and contact time. Strength is about ratio. Fix them separately.
How to Apply It Without a Refractometer
Pick a baseline recipe and change one variable at a time. For a V60:
- Start at 15 g coffee, 250 g water (1:16.7), 93°C water, medium grind (like coarse table salt). Aim for the full brew to finish in 2:45–3:15.
- Taste it. Decide: sour, balanced, or bitter?
- If sour, grind one notch finer. If bitter, grind one notch coarser. Keep the ratio identical.
- Re-brew. Repeat until the cup tastes sweet and clean with no sharp edges.
That single loop walks you across the brewing control chart by feel.
Do You Actually Need a Refractometer?
A coffee refractometer (VST or DiFluid) costs $150–$700. It measures TDS in seconds, then a free app calculates extraction yield. Useful? Yes. Necessary? No.
Buy one if you are dialing in three or more new coffees per month, or you cannot tell sour from bitter yet and want objective feedback. Skip it if you brew the same beans for two weeks at a time — your tongue will catch up faster than the gear pays off.
Quick Reference Checklist
- Ratio: V60 at 1:16.7, AeroPress at 1:14–1:16, Chemex at 1:16–1:17.
- Water temperature: 92–96°C (198–205°F), measured, not guessed.
- Total brew time: V60 2:45–3:15, AeroPress 1:30–2:00, Chemex 4:00–5:00.
- Grind check: sour cup → finer; bitter cup → coarser. Change nothing else that brew.
- Taste log: write the grind setting and the verdict (sour / balanced / bitter) after every cup.
Your single next step today: brew your usual recipe, write down whether it tastes sour, balanced, or bitter, then change only the grind size on your next brew. That one habit puts you inside the 18–22% window faster than any new gadget.