Kaiserblick Knowledge

Extraction

7 min read

Extraction

Sources: The Coffee Brewing Handbook by Rob Lingle (SCA, 2011); Espresso Extraction: Measurement and Mastery by Scott Rao (2013); The Physics of Filter Coffee by Jonathan Gagné (2020)

Extraction, or solubles yield, measures how much of the available flavouring material in ground coffee was removed and dissolved into the brew. It is expressed as a percentage of the total ground coffee weight used. (source: SCA Coffee Brewing Handbook)

How Extraction Works

Approximately 28–32% of roasted bean mass can theoretically be dissolved in water — the exact fraction depends on roast level and brewing method. The remaining mass is cellulose bean fibre and other water-insoluble structures. The water-soluble fraction contains all the flavouring compounds responsible for taste and aroma. (source: The Physics of Filter Coffee by Jonathan Gagné (2020))

These compounds dissolve at different rates. During brewing, the chemical composition of the beverage changes continuously — the most flavourful compounds extract first. Prolonged contact time releases progressively less desirable compounds. The optimum brew is therefore stopped before maximum extraction is reached.

Physical Mechanisms: Advection and Diffusion

Two physical mechanisms transport solubles from coffee particles into the beverage — see Advection and Diffusion for detail:

  • Advection (percolation only): flowing water sweeps solubles away from particle surfaces — fast
  • Diffusion: concentration gradient drives solubles from particle interior to surface — slow; this is the rate-limiting step

Hotter water increases diffusion rates for all compounds but changes their relative rates — meaning temperature shifts the flavor profile, not just the speed of extraction. Two brews at the same AEY but different temperatures taste different for this reason. (source: The Physics of Filter Coffee by Jonathan Gagné (2020))

The Three Phases of Brewing

  1. Wetting: Bean fibre absorbs water; CO₂ and other gases are driven from the particles; prepares grounds for extraction.
  2. Extraction: Water-soluble flavouring compounds dissolve rapidly, migrating out of the bean fibre into the water.
  3. Hydrolysis: Large insoluble carbohydrate molecules break down into smaller water-soluble reducing sugars and proteins — only occurs with prolonged contact.

The Extraction Range

Repeated studies by the CBC and Nordic Coffee Brewing Center confirmed three principles:

Extraction Zone% Solubles YieldTaste Characteristics
Under-developedBelow 18%Grassy, peanut-like, thin
Ideal18–22%Balanced, complex, sweet
Over-extractedAbove 22%Bitter, astringent, harsh

The bitterness and astringency of over-extraction results from the build-up of chlorogenic acids and phenolic compounds during the later stages of brewing. The most desirable mixture of flavour elements occurs before the maximum amount of material is removed. (source: The Coffee Brewing Handbook by Rob Lingle (SCA, 2011))

Shifting upper bound in specialty coffee: Gagné’s empirical data suggest the 22% upper limit has shifted upward for high-quality grinders and specialty-grade green coffee. He personally finds good cups at 22–23.5% AEY when using uniform-distribution burr sets, and notes some influencers in specialty coffee prefer even higher values. The lower bound of ~18% appears stable, but taste preference near 15% and dispreference from 15–18% suggest a non-linear preference curve rather than a simple gradient. The 18–22% range remains a practical starting target, not an absolute ceiling. (source: The Physics of Filter Coffee by Jonathan Gagné (2020))

Extraction Rate Over Time

The extraction curve is not linear. Research shows:

  • First 2 minutes: ~65–75% of available soluble material extracts — this fraction has the best flavour, highest solubles concentration, highest acidity (lowest pH)
  • Minutes 2–5: Modest additional extraction; diminishing returns in quality
  • Beyond 5 minutes: The brew has removed more than 80% of available soluble material (~24% yield). Unless a coarse enough grind is used, flavours become bitter and astringent.

This explains why brewing time must be matched to grind size: a fine grind in a long-cycle brewer will over-extract; a coarse grind in a short-cycle brewer will under-extract. See Grind.

Extraction and Roast Level

Roast level affects extraction behaviour:

  • Light roasts are denser and more physically resilient than dark roasts. Their harder structure means water penetrates more slowly. Light roasts may require slightly finer grind or longer time to reach optimal extraction.
  • Dark roasts are more brittle and porous; they extract more rapidly. Higher phenol content in dark roasts means over-extraction tastes more astringent.
  • Trigonelline (a bitter compound) survives fully in light roasts but degrades ~80% in medium-dark roasts. Its extraction in the first 2 minutes of brewing is a marker of light roast quality. (source: The Coffee Brewing Handbook by Rob Lingle (SCA, 2011))

Darker roasts produce lower AEY in filter brewing: Gagné’s empirical data across many origins and brew times show a clear correlation — darker-roasted coffees (measured by bean color/roast development) consistently reach lower average extraction yields than lighter-roasted coffees when brewed identically. This is the opposite of what simpler models predict (darker = more brittle = easier extraction). The effect holds even when controlling for brew time. Natural process coffees extract slightly lower on average than washed; decaffeinated coffees extract significantly lower due to prior chemical depletion. (source: The Physics of Filter Coffee by Jonathan Gagné (2020))

Extraction and Strength: The Relationship

Extraction and strength (TDS) are related but distinct. It is possible to:

  • Extract a large amount of material and dissolve it in little water → high strength, over-extracted taste
  • Extract a small amount of material and dissolve it in a large volume → low strength, under-developed taste

The Coffee Brewing Control Chart maps the three-way relationship. The brewing formula (coffee-to-water ratio) constrains which strength-extraction combinations are achievable simultaneously. Only the ideal brewing formula enables both ideal extraction and ideal strength at the same time.

Measuring Extraction

To calculate extraction yield, you need to know the solubles concentration (measured by TDS meter) and the brewing formula used. The CBI developed a formula from which the CBC published conversion tables. Modern TDS meters allow direct, rapid measurement of solubles concentration in the beverage, from which extraction yield is calculated via the chart.

The oven-dehydration method (the original laboratory technique) remains the most precise: a 10ml beverage sample is dried at 105–110°C for 3 hours; the residue weight × 10 = % solubles concentration.

For espresso, the Coffee Refractometer is the standard industry instrument. It measures %TDS directly and, combined with VST Coffee Tools software (accounting for CO₂ content, liquid retained in grounds, and moisture content), yields accurate extraction % calculations. (source: Espresso Extraction: Measurement and Mastery by Scott Rao (2013))

Espresso Extraction

Espresso targets a narrower extraction window than filter: 19–20% rather than 18–22%. The higher pressure and shorter contact time make espresso more sensitive to variable interactions — any suboptimal setting reduces extraction. Underextraction is the default risk for a normale; overextraction is rare except with lungo ratios.

The brewing ratio (finished shot weight ÷ dry dose weight) is the primary lever for adjusting both strength and extraction simultaneously. A 1.5–2.0× ratio is the normale range. See Espresso Extraction for the full parameter set.

Relevance to Kaiserblick

Understanding extraction is essential for Kaiserblick’s coffee shop and roaster customers. Kaiserblick’s light roast specialty coffees require careful grind calibration to reach the 18–22% ideal extraction range. Under-extraction (below 18%) is a particular risk with light roasts brewed with a grind that is too coarse — resulting in the grassy, peanut flavours that mask the varietal and origin character of the coffee.

Kaiserblick’s positioning around single-origin, micro-lot light roasts means that reaching ideal extraction is essential to delivering the flavour promise of the coffee — over- or under-extraction will produce a cup that does not reflect the work invested in farming, processing, and roasting.

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