TDS (Total Dissolved Solids) measures the concentration of dissolved coffee compounds in your brewed coffee, expressed as a percentage. It tells you how strong or weak your coffee is. A refractometer measures TDS by analyzing how light bends through the coffee sample. For pour over coffee, an ideal TDS range is 1.15%–1.45% according to SCA Gold Cup standards. Espresso typically ranges from 7%–12% TDS due to its concentrated nature. Monitoring TDS helps you achieve consistent flavor and mouthfeel across brews.

Extraction Yield (EY) is calculated using the formula:
EY% = (TDS% × Beverage Yield in grams) ÷ Coffee Dose in grams

For example, if you brew 20g of coffee, get 300g of liquid coffee output, and your refractometer reads 1.30% TDS, then:
EY = (1.30 × 300) ÷ 20 = 19.5%

This falls within the SCA Gold Cup ideal range of 18%–22%, indicating a well-extracted brew. Extraction yield tells you how much of the coffee grounds dissolved into the water — too low and the coffee tastes sour/underdeveloped; too high and it tastes bitter/astringent.

The Specialty Coffee Association (SCA) Gold Cup Standard defines the optimal brewing parameters for filter/drip coffee: an extraction yield of 18%–22% and a TDS of 1.15%–1.35% (sometimes extended to 1.45%). These standards were developed through extensive sensory research to identify the range where coffee tastes balanced, sweet, and complex — avoiding sourness (under-extraction) and bitterness (over-extraction). While these standards were designed for filter coffee, the extraction yield range of 18%–22% is widely used as a benchmark across most brew methods.

To get accurate TDS readings from your refractometer (like VST LAB Coffee Refractometer or Atago Coffee PAL):
1. Calibrate first with distilled water (should read 0.00% TDS).
2. Cool the sample to near room temperature — hot coffee can damage the prism and give inaccurate readings.
3. Stir the coffee thoroughly before sampling to ensure uniformity.
4. Use a clean pipette to place a few drops on the prism.
5. Take multiple readings and average them for best accuracy.
6. Clean the prism immediately after each use with distilled water and a microfiber cloth.

Brew Ratio is the relationship between your coffee dose and beverage yield, expressed as 1:X (e.g., 1:15 means 1g of coffee produces 15g of brewed coffee). For pour over, common ratios are 1:15 to 1:17. For espresso, typical ratios are 1:2 to 1:3. Brew ratio directly affects both TDS and extraction yield — a tighter ratio (less water) produces stronger, more concentrated coffee; a wider ratio (more water) produces weaker coffee but can increase extraction yield. Finding the right brew ratio is key to dialing in your perfect cup.

If your extraction yield is below 18%, your coffee is under-extracted and may taste sour, salty, or hollow. To increase extraction:
• Grind finer — increases surface area for water contact
• Increase brew time — allows more compounds to dissolve
• Use hotter water — speeds up extraction (ideal: 195°F–205°F / 90°C–96°C)
• Agitate more — stirring or swirling improves extraction uniformity
• Use more water (wider brew ratio) — more solvent pulls more solubles

If your extraction yield is above 22%, your coffee is over-extracted and may taste bitter, dry, or astringent. To decrease extraction:
• Grind coarser — reduces surface area
• Shorten brew time — limits compound dissolution
• Use cooler water — slows extraction rate
• Reduce agitation — less disturbance means slower extraction
• Use less water (tighter brew ratio) — less solvent available

Yes! While 18%–22% extraction yield is a universal starting point, different coffees may taste best at slightly different extraction levels:
• Light roasts are denser and harder to extract — they often taste best at the higher end (20%–22.5%) to fully develop their floral and fruity notes.
• Dark roasts are more porous and extract easily — they may taste best at the lower end (17.5%–20%) to avoid excessive bitterness.
• African coffees (Ethiopian, Kenyan) often shine at higher extractions, while Brazilian or Sumatran coffees may prefer slightly lower extractions.
Always use extraction yield as a guideline, not an absolute rule — let your taste buds be the final judge!

Yes, this calculator is still very useful without a refractometer! You can experiment with hypothetical TDS values to understand how changes in dose, yield, or TDS affect extraction yield. This helps you learn the relationships between variables. For example, you can see that increasing your beverage yield from 280g to 320g (while keeping dose and TDS constant) raises extraction yield. Many professional baristas use this tool as a learning aid to build intuition about extraction mechanics before investing in a refractometer.

Brew Water is the total amount of water you pour over the coffee grounds. Beverage Yield (also called output or liquid coffee) is what ends up in your cup — it's always less than brew water because coffee grounds retain about 2× their weight in water. For example, with 20g of coffee and 340g of brew water, your beverage yield might be around 300g (20g × 2 = 40g absorbed). Extraction yield must be calculated using beverage yield, not brew water, because TDS is measured from the liquid coffee output. Always weigh your final cup to get the correct beverage yield for accurate extraction calculations.