Coffee Extraction: Understanding TDS, Yield and Concentration

Ever wondered why your coffee sometimes tastes weak, sour, or overly bitter—even when you follow the recipe? The secret lies not just in your technique, but in the invisible chemistry of what’s pulled from the beans. Understanding how much of the coffee’s soluble material ends up in your cup, and in what balance, is the key to consistently great brews.

In short: only around 30% of a coffee bean is made up of soluble compounds that contribute to flavor—some good, some not. Extraction yield and concentration (TDS) determine what ends up in your cup. The Specialty Coffee community generally recommends a TDS (total dissolved solids) between 1.15%–1.35% and an extraction yield that balances strength and clarity.

What Is in a Coffee Bean? Solubles and Limits

A typical roasted coffee bean is about 30% soluble material. These dissolved solids include both desirable aromatic and flavorful compounds, as well as undesirable ones. That means simply extracting more doesn’t guarantee better flavor—it’s about extracting the right balance. Equally important is achieving an ideal concentration, which significantly shapes how all those extracted compounds are perceived on the palate.

How Do You Measure Coffee Concentration (TDS)?

There are three common ways to measure the concentration of dissolved solids in your brewed coffee—that is, its Total Dissolved Solids (TDS)—usually expressed as a percentage:

• VST Refractometer: Measures how light refracts through the coffee liquid and converts that to a TDS value in %. For example, water reads 0.1%, while a typical coffee might register around 1.3% (often rounded to 1.2% for convenience).
• Conductivity Pen (TDS Meter): Measures the electrical conductivity of the liquid, primarily from electrolytes, which make up about 10% of dissolved solids. This reading is then converted to ppm (parts per million), and further estimated into a TDS percentage. For instance, water might show 100ppm, and coffee around 1300ppm, calculated to roughly 1.2% TDS. This method is more laborious.
• Evaporation Method: The coffee liquid is dried and weighed to determine the mass of dissolved solids directly. This yields the most accurate TDS, but demands controlled lab-like conditions.

Note: ppm stands for parts per million—for example, 1ppm means 1mg of solute per kg (1,000,000mg) of solution. It's a ratio just like percentages, just scaled up. SCAA recommends a TDS range of 1.15%–1.35% for optimal flavor, and SCAE suggests 1.2%–1.45%.

How Is Extraction Yield Calculated?

Extraction yield refers to the percentage of the coffee bean’s soluble material that ends up in your brewed cup. It is typically calculated using one of the following methods, depending on your brewing style:

• VST/Conductivity-Based Formula: (TDS reading × Coffee Liquid Weight) ÷ Coffee Grounds Weight
• Dry Solids Method: (Weight of dried coffee solids ÷ Coffee Grounds Weight)

Note: The dry solids method is the most accurate, but requires completely drying the brewed coffee, which is less practical. Meanwhile, the VST and conductivity methods can overlook variables like coffee's water absorption during brewing.

Brew Method Adjustments: How to Calculate Yield per System

To tailor your extraction math to different brewing styles, use these adjusted formulas—assuming water TDS is negligible (otherwise subtract it from your readings):

• Immersion Methods (e.g., French Press, Clever Dripper, Cupping):
  (Brew Water Weight × TDS %) ÷ Coffee Grounds Weight
  Example: (240g × 1.2%) ÷ 15g = 19.2% extraction yield
• Filter Methods (e.g., Pour Over, Chemex, AeroPress, Cloth Filter):
  (Coffee Liquid Weight × TDS %) ÷ Coffee Grounds Weight
  Or: [(Brew Water Weight − Coffee Absorption) × TDS %] ÷ Coffee Grounds Weight
  (Standard coffee absorption is roughly 2× the weight of coffee grounds)
  Example: [280g × 1.2%] ÷ 15g = 22.4% OR [(280g − 30g) × 1.2%] ÷ 15g = 20% yield
• Espresso:
  (Espresso Liquid Weight × TDS %) ÷ Coffee Grounds Weight
  (Always filter out suspended solids before measuring TDS; use VST filter or a substitute like paper filter.)
  Example: (36g × 10%) ÷ 18g = 20% extraction yield

Why These Numbers Matter

The balance between extraction yield and concentration (TDS) defines whether your coffee tastes balanced, underdeveloped, or over-extracted. Too low an extraction and you get sour, sharp, underdeveloped flavors; too high, and you risk bitterness and astringency. The ‘Gold Cup’ standard recommended by the SCAA and SCAE provides a reliable flavor window: a TDS between 1.15%–1.35% or 1.2%–1.45%, paired with an extraction yield that complements the brew method.

Frequently Asked Questions

What is TDS in coffee and how is it measured?

TDS stands for Total Dissolved Solids, the percentage of soluble material in your brewed coffee. It’s commonly measured using a VST refractometer (showing %), a conductivity pen (reporting in ppm, then converted), or by fully evaporating the liquid and weighing the residue. Most specialty coffee recommendations fall between 1.15%–1.35% TDS.

What is coffee extraction yield?

Extraction yield is the percentage of soluble coffee material extracted from the roasted beans during brewing. It is calculated based on your brew’s TDS, the weight of coffee used, and the final beverage weight—adjusted slightly depending on your brew method (immersion, filter, or espresso).

How do I calculate extraction for a pour-over?

For pour-over, use either: (coffee liquid weight × TDS %) ÷ coffee grounds weight, or account for water absorbed by coffee (usually 2× the coffee weight) with: [(water weight − 30g absorption) × TDS %] ÷ coffee weight. Example: [280g × 1.2%] ÷ 15g ≈ 22.4% yield.

What TDS range is ideal for good coffee flavor?

The Specialty Coffee Association recommends a TDS between 1.15% and 1.35% for balanced flavor, with an acceptable extended range up to 1.45%. This ensures enough extracted material for body and complexity, without excessive bitterness or sourness.

Does espresso need a different extraction calculation?

Yes. For espresso, first filter out any suspended solids using a specialized VST filter or paper filter. Then use: (espresso liquid weight × TDS %) ÷ coffee grounds weight. For example, 36g of espresso at 10% TDS using 18g coffee yields 20% extraction.

Which measurement method is most accurate for TDS?

The evaporation (drying) method is the most accurate as it directly weighs the dissolved coffee content. However, VST refractometers and conductivity pens are more practical for daily use, though they may ignore factors like water absorption or conductivity from non-soluble ions.

FrontStreet Coffee Beans Ideal for Studying Extraction

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