Definition
Extraction is the process by which water dissolves and carries away soluble compounds from ground coffee. In pour-over brewing, this occurs as water passes through a bed of coffee grounds, dissolving material along the way.1
Extraction is typically expressed as a percentage: the ratio of dissolved coffee solids to the dry mass of the coffee grounds used. An extraction of 20% means that 20% of the coffee's mass has been dissolved into the water.
Key Insight
Extraction percentage is independent of strength. A light-bodied cup can have high extraction, and a strong cup can have low extraction. These are separate dimensions.2
Mechanism
Extraction occurs in stages. Different compounds dissolve at different rates based on their solubility and molecular weight:3
- •Early extraction (0-10%): Acids and light aromatics dissolve quickly. These compounds contribute brightness and fruity notes.4
- •Mid extraction (10-20%): Sugars and balanced aromatics. This range typically produces sweetness and complexity.
- •Late extraction (20%+): Bitter compounds and heavier phenols. These add body but can overwhelm at high concentrations.5
The goal in pour-over is typically to extract primarily from the first two stages while minimizing contribution from the third.
Measurement
Extraction percentage is calculated using total dissolved solids (TDS) and brew ratio:
Extraction % = (Brewed Coffee Mass × TDS) ÷ Dry Coffee Mass
Example: 300g brewed coffee at 1.35% TDS from 20g dry coffee = 20.25% extraction
TDS is measured using a refractometer, which provides a precise quantification of dissolved solids.
Practical Note: Most home brewers do not have access to measurement tools like a refractometer. Extraction can instead be evaluated by taste, which is ultimately the most important measure of success. Key sensory indicators include:
- •Underextracted coffee: sour, thin, or hollow flavors
- •Well-extracted coffee: balanced sweetness, clarity, and complexity
- •Overextracted coffee: bitterness, dryness, or heavy astringency
By adjusting grind size, pour technique, brew ratio, or temperature and tasting the result, brewers can iteratively reach a preferred extraction without technical instruments. Taste is the reference point that ties all brewing variables together.
Optimal Range
The Specialty Coffee Association suggests an optimal extraction range of 18-22% for filter coffee.6 This is a guideline, not a rule.
In practice:
- •Light roasts may taste best at 20-22%7
- •Medium roasts often prefer 19-21%
- •Darker roasts can be optimal at 18-20%
These ranges overlap significantly. Roast level, processing method, and personal preference all affect the ideal extraction point.
References & Notes
- 1.
The extraction process is governed by diffusion kinetics, where soluble compounds migrate from ground coffee particles into water driven by concentration gradients. This follows Fick's laws of diffusion, with extraction rate proportional to surface area, temperature, and the concentration differential between particle interior and surrounding water. See Illy, A., & Viani, R. (2005). Espresso Coffee: The Science of Quality (2nd ed.).
- 2.
Extraction yield and beverage strength (TDS) are orthogonal variables in the Coffee Brewing Control Chart developed by Lockhart (1957) and later refined by the Specialty Coffee Association. A 15% extraction at 1:10 ratio produces 1.5% TDS, while a 22% extraction at 1:17 ratio also produces ~1.3% TDS - similar strength, vastly different extraction. This independence is fundamental to understanding brewing control.
- 3.
Extraction follows a predictable compound-class sequence based on molecular weight and solubility. Organic acids (citric, malic, chlorogenic acids) dissolve first due to high water solubility. Sugars (sucrose, reducing sugars) follow in the mid-extraction phase. High-molecular-weight melanoidins, chlorogenic acid lactones, and quinides extract last. Research by Navarini et al. (2009) demonstrates this temporal stratification through chromatographic analysis of extraction phases.
- 4.
Early-phase acids include quinic acid, citric acid, malic acid, and phosphoric acid, which contribute perceived acidity and brightness. Light aromatics in this phase include esters, aldehydes, and ketones responsible for fruited and floral notes. These compounds have high vapor pressure and solubility, extracting within the first 30 seconds of contact time in typical pour-over scenarios.
- 5.
Late-extraction bitterness primarily derives from chlorogenic acid lactones (formed during roasting via Maillard reactions) and quinides. These compounds have lower solubility and higher molecular weight, requiring extended contact time and elevated temperature for significant extraction. Overextraction (>24%) correlates with excessive concentrations of these compounds, leading to persistent bitterness and astringency. World Barista Championship analysis (2015-2024) shows winning recipes cluster at 19.5-21.5% extraction, deliberately avoiding this late-phase extraction zone.
- 6.
The SCA's 18-22% optimal range was established through sensory analysis correlating extraction percentages with trained panel preferences. This range represents the "Golden Cup" standard originally developed by Lockhart (1957) at MIT and refined over decades. However, the range is a statistical average - individual coffee characteristics, roast profiles, and consumer preferences create significant variation. Modern specialty coffee increasingly pushes beyond this range, with some World Brewers Cup recipes achieving 22-24% extraction on specific coffees.
- 7.
Light roasts retain denser cellular structure due to shorter roast development, creating higher solubility barriers. Higher extraction percentages (20-22%) are typically required to access the full flavor complexity locked within these denser particle structures. This contrasts with dark roasts, where extended roasting creates more porous, friable structures with lower extraction barriers. Temperature also plays a critical role: light roasts often benefit from 96-98°C brewing temperature to overcome solubility limitations, while dark roasts may be optimal at 88-92°C to avoid over-extracting bitter melanoidins.