TDS (Total Dissolved Solids) & Extraction Yield¶
TDS (Total Dissolved Solids) The concentration of dissolved coffee solids in brewed coffee. Measured as percentage. Typical range: 1.15-1.45% for filter coffee, 8-12% for espresso. Indicates strength, not quality. Refractometer Optical device measuring TDS in brewed coffee. Light refracts differently through dissolved solids. Digital refractometers (VST, Atago) give precise TDS readings. Essential tool for brew analysis. VST Refractometer Industry-standard digital refractometer designed specifically for coffee. Uses specific algorithm for coffee solids. More accurate than general refractometers. Gold standard in specialty coffee. Expensive ($500-700). Atago Refractometer Alternative digital refractometer used in coffee. Coffee-specific models available. Slightly lower cost than VST but very accurate. Popular in specialty coffee. Extraction Yield (Extraction %) The percentage of coffee mass extracted into the brew. Calculated from TDS, brew weight, and coffee dose. Ideal range: 18-22%. Below 18% = under-extracted; above 22% = over-extracted. Extraction Formula EY% = (Brew Weight × TDS%) / Coffee Dose × 100 Example: (300g × 1.30%) / 20g × 100 = 19.5% extraction yield Brew Strength The concentration of dissolved coffee in the beverage. Same as TDS. Independent of extraction yield - can have strong but under-extracted coffee, or weak but properly extracted coffee. Extraction vs Strength Extraction = how much of the coffee was dissolved (18-22% ideal). Strength = how concentrated the brew is (1.15-1.45% for filter). Can adjust each independently through grind size and ratio. SCAA/SCA Brewing Standards Recommended ranges from Specialty Coffee Association: TDS 1.15-1.35%, Extraction Yield 18-22%. "Golden Cup" target historically 1.15-1.25% TDS. Modern specialty often exceeds these ranges. Under-extraction Extraction yield below 18%. Sour, salty, grassy, underdeveloped flavors. Occurs from: too coarse grind, too fast brew, water too cool, insufficient contact time. Over-extraction Extraction yield above 22%. Bitter, astringent, hollow, dried flavors. Occurs from: too fine grind, too slow brew, water too hot, excessive contact time. Ideal Extraction Range 18-22% extraction yield with balanced flavor. Sweet spot varies by origin, roast, and personal preference. Most specialty filter coffee: 19-21%. Brew Ratio Impact Changing ratio affects strength but can maintain extraction. Example: 1:15 ratio = stronger cup; 1:17 ratio = weaker cup. Extraction yield similar if other variables constant. Grind Size Impact Finer grind increases extraction (more surface area). Coarser grind decreases extraction. Primary variable for adjusting extraction yield without changing strength. Coffee Brewing Control Chart Graph plotting TDS (strength) against Extraction Yield. Shows ideal zone, over-extraction zone, under-extraction zone. Tool for brew analysis and adjustment. Created by Lockhart/SCAA. Optimal Brew Coffee meeting both strength and extraction targets. Typically 1.20-1.35% TDS and 18.5-21% extraction for filter coffee. Sweet, balanced, clear, complex flavors. Sour (Under-extracted Indicator) Taste indicating insufficient extraction. Sourness from uncomplemented acids. Fix by grinding finer, increasing temperature, or extending time. Bitter (Over-extracted Indicator) Taste indicating excessive extraction. Bitterness from over-extracted compounds (chlorogenic acid breakdown, quinic acid). Fix by grinding coarser, decreasing temperature, or shortening time. Sweet Spot The grind size and parameters producing balanced, sweet, complex extraction. Neither sour nor bitter. Usually in 19-21% extraction range. Goal of dialing in. Evenness of Extraction Uniformity of extraction across all coffee particles. Ideal: all particles in the sweet spot. Reality: distribution with some under-extracted (fines) and over-extracted (boulders). Grind consistency crucial. Dialing In (Brew Context) Process of finding optimal grind size and parameters for specific coffee and brewing method. Involves tasting, measuring TDS, calculating extraction, and adjusting. Temperature's Impact Higher temperature increases extraction rate. Typical: 1-2% extraction yield difference per 3-5°C change. Lighter roasts benefit from higher temps (95-96°C); darker from lower (90-93°C). Contact Time Duration water is in contact with coffee grounds. Longer contact time increases extraction. Must balance against temperature drop and other variables. Turbulence/Agitation Impact Stirring or agitation increases extraction rate by renewing water contact with grounds. Can improve evenness but risks channeling or over-extraction if excessive. Batch Size Effect Smaller batches often extract more efficiently (better water-to-coffee contact). Scaling recipes isn't always linear. May need grind or technique adjustments for different batch sizes. Coffee Solubility Approximately 28-30% of roasted coffee is water-soluble. Remaining 70% is insoluble cellulose and fiber. Extraction yield measured as % of total mass, not soluble fraction. Selective Extraction Concept that different compounds extract at different rates. Early extraction: acids, sugars, lighter aromatics. Late extraction: heavier aromatics, bitter compounds. Affects extraction strategy. Brew Water Mass Total water used in brewing including water absorbed by grounds. Absorbed water (roughly 2g per 1g coffee) doesn't appear in final brew. Must account for when calculating ratios and yields.
Related Notes: - Coffee Terminology MoC