Brewing by Extraction Yield and TDS: A Cup You Reproduce with Numbers

The same beans, yet the taste differs every time you brew. Chase the cause on feel alone and you get lost. What pros use are two numbers — TDS (strength) and extraction yield (EY). Understand these two axes and you can decide "what to change next" logically.

Two numbers: strength (TDS) and yield (EY)

TDS (Total Dissolved Solids) is the proportion (%) of solids dissolved in the finished coffee. It decides the "strong/weak" when you drink. Extraction Yield, on the other hand, is what % of the bean's compounds you dissolved into the water. This is what decides the "direction" of the taste.

• Low TDS = weak, high = strong (strength)
• Low yield (below ~18%) = under-extraction: sour, salty, lacking
• High yield (over 22%) = over-extraction: astringent, bitter, dry with off-flavors
• Yield 18–22% = the "golden zone" where sweetness and complexity coexist

The golden cup as a standard

The "coordinates of deliciousness" laid out by the SCA (Specialty Coffee Association) is the golden cup. Land within the frame of TDS 1.15–1.35% and extraction yield 18–22% and most people feel it is "well balanced."

Translating numbers into taste

Most taste complaints can be explained by too much or too little yield. You only need to remember two directions.

• Sour, salty, watery → under-extracted. Raise the yield (grind finer / raise the temperature / extend the time / agitate)
• Astringent, bitter, mouth-drying → over-extracted. Lower the yield (grind coarser / lower the temperature / shorten the time)
• Taste is good but thin/strong → a strength (TDS) issue. Adjust with the grounds-to-water ratio

Five levers that move the yield

• Grind: the finer, the more surface area, the higher the yield (the most effective)
• Water temperature: the higher, the more readily compounds dissolve, the higher the yield
• Contact time: the longer, the higher the yield
• Agitation (stirring): the stronger, the higher the yield
• Grounds-to-water ratio: mainly moves the strength (TDS)

Should you measure TDS?

With a refractometer (VST, Atago, DiFluid, etc.) you can manage TDS as an objective number, but it is not essential. For most people the biggest single step is "using a scale." Just fixing the dose, water amount and brew time every time keeps the yield naturally within a certain range and secures 80% of repeatability.

Once you fix the ratio, next change only one thing. Grind one step finer, and if the acidity settles and it gets sweeter, that is proof the yield went up. Recording "changed → how it changed" this way connects numbers and taste in your head.

Grasp extraction by the "numbers" and your improvement accelerates at a stroke. Not denying feel, but giving feel coordinates — that is the tool of TDS and yield.