Brew ratios: the Golden Cup targets and what home brewers use
The Specialty Coffee Association's (SCA) Golden Cup standard is widely cited as targeting a brew strength (TDS) of 1.15–1.35% and an extraction yield of 18–22%. A starting ratio often mentioned for hitting that target is about 55 g of coffee per liter of water (roughly 1:18), while home pour-over brewers commonly use 1:15–1:17 depending on taste. The figures in the table below are reference values that home brewers commonly use as starting points — not SCA specifications.
| Brew Method | Recommended Ratio | Grind Particle Size | Water Temp | Target TDS |
|---|---|---|---|---|
| Pour Over (V60, Kalita) | 1 : 15 ~ 1 : 16.5 | Medium-Fine (600~800 μm) | 92 ~ 94°C (198~201°F) | 1.25 ~ 1.40% |
| Iced Pour Over | 1 : 10 (+ 100g Ice) | Medium (800~900 μm) | 93 ~ 95°C (200~203°F) | 1.30 ~ 1.45% |
| AeroPress | 1 : 12 ~ 1 : 14 | Fine-Medium (400~600 μm) | 85 ~ 88°C (185~190°F) | 1.35 ~ 1.50% |
| French Press | 1 : 15 | Coarse (1000~1200 μm) | 94 ~ 96°C (201~205°F) | 1.20 ~ 1.35% |
| Cold Brew (Immersion) | 1 : 8 ~ 1 : 10 | Extra Coarse (1200 μm+) | Cold / Room Temp | 1.40 ~ 1.65% (Conc.) |
| Moka Pot | 1 : 7 | Fine (300~500 μm) | Low Stove Heat | 1.50 ~ 2.00% |
1. The Fluid Dynamics of Blooming: Degassing Trapped CO2
Freshly roasted whole-bean coffee traps large quantities of carbon dioxide within its cellular cellulose matrix. When hot water first contacts freshly ground coffee, the gas rapidly expands and escapes. Introducing a 30 to 45-second bloom with approximately 2 to 2.5 times the coffee weight in water ensures that gas voids collapse. Without a proper bloom, escaping gases form hydrophobic barrier pockets that cause channeling, forcing bypass water through micro-cracks and yielding an uneven, bitter-sour extraction.
2. Diagnosing Extraction Defects: Over vs Under Extraction
If your cup does not taste balanced, refer to the diagnostic troubleshooting matrix below and adjust only one extraction variable at a time:
| Sensory Symptom | Probable Cause | Corrective Action |
|---|---|---|
| Sharp, sour, vegetal, hollow finish | Under-extraction (Inadequate solubles dissolved) | Finer grind setting, increase water temperature by 1~2°C, or extend total contact time. |
| Drying mouthfeel, harsh bitterness, ashy aftertaste | Over-extraction (Undesirable heavy tannins pulled) | Coarser grind setting, lower water temperature, or shorten contact time. |
| Muddy texture, cloudy cup as it cools | Excess fines clogging paper filter | Calibrate burr alignment, sift excess micro-fines, or rinse paper filter prior to brewing. |
3. Water Chemistry: The Solvent Behind Every Note
Because water accounts for more than 98% of your brewed cup, its mineral composition governs what flavor compounds are drawn into solution:
- Water TDS (commonly cited: about 75–250 ppm, target around 150 ppm): Water devoid of minerals (distilled or pure reverse osmosis) lacks the ionic affinity required to bind flavor compounds, resulting in flat and dull cups. Water exceeding 250 ppm masks delicate floral notes with chalky chalkiness.
- Magnesium vs Calcium: Magnesium ions (Mg²⁺) strongly pull crisp fruit acids and aromatic monoterpenes, whereas Calcium ions (Ca²⁺) bond with creamy sweetness and viscous body.
- Brewing Temperature Dynamics: Temperatures below 90°C (194°F) highlight delicate citric acid and brightness, whereas temperatures above 94°C (201°F) accelerate dissolution of caramelized sugars, body, and roasty notes.
4. Frequently Asked Questions (FAQ)
A. Coffee grounds physically retain approximately 2 grams of water per gram of dry coffee. For a 20g dose, approximately 40 ml of water stays trapped in the spent coffee bed as absorption yield loss.
A. White oxygen-bleached filters have minimal paper taste, but unbleached brown kraft filters impart noticeable cardboard aromatics unless rinsed thoroughly with hot water prior to adding coffee grounds.
A. The hot extract drains directly onto 100~120g of ice cubes. Melting ice rapidly cools and dilutes the coffee to the perfect 1:15~1:16 drinking strength while trapping volatile aroma vapors that would otherwise evaporate.