Coffee Concentration and Extraction Rate

Two essential factors influencing the quality of pour-over coffee are coffee concentration and extraction rate.

For the basic extraction concept behind concentration and extraction rate, start with What Is Coffee Extraction?.

Understanding Coffee Concentration & Extraction Rate

• Coffee Concentration: If concentration is too low, coffee tastes weak and flavorless; if too high, it becomes overwhelming and unpleasant.
• Extraction Rate: Under-extracted coffee is sour and lacks complexity, while over-extracted coffee tastes bitter and astringent.

As extraction rate increases, concentration also rises, intensifying the flavor. Initially, sweet and fruity acidity dominates, but gradually, bitterness emerges and can eventually overpower the coffee, resulting in an unpleasant drinking experience.

Golden Cup Standard

The Golden Cup Standard was initially proposed by Dr. Earl E. Lockhart of MIT in the 1960s and later revised. Today, it varies slightly across different regions but is generally based on extensive market research. It identifies the ideal range of coffee concentration and extraction that most people find enjoyable:

• Coffee Concentration: 1.15% – 1.55%
  • Below 1.15%: Coffee tastes weak and watery.
  • Above 1.55%: Coffee tastes excessively strong and unpleasant.
• Coffee Extraction Rate: 18% – 22%
  • Soluble compounds represent only about 30% of coffee beans by weight.
  • Extraction below 18% results in sourness and underdeveloped flavors.
  • Extraction above 22% creates bitterness and astringency.

Example of Golden Cup Standard Calculation:

If you're brewing coffee with 20 grams of coffee grounds and want 300 ml of brewed coffee, here's a theoretical example that meets the Golden Cup criteria:

• Extraction Rate: 20%
• 20 grams coffee × 20% extraction = 4 grams extracted coffee solids.
• Coffee Concentration: 1.33%
• 300 ml coffee liquid × 1.33% = 4 grams dissolved solids in the coffee.

Achieving these ideal values requires careful control of various brewing factors, including:

• Grind size
• Brew ratio (coffee-to-water ratio)
• Water temperature
• Extraction time
• Brewing technique
• Roast level

Influence of Pouring Height on Extraction

Pouring height directly impacts extraction due to gravity. Higher pouring heights increase water impact, enhancing extraction efficiency. Conversely, lower heights reduce gravity’s influence, thus decreasing extraction.

• Higher pouring height:
  • Boosts extraction efficiency.
  • However, the top layer of coffee grounds risks over-extraction due to increased agitation from falling water.
  • Over-extraction becomes more evident with increased water flow and pouring height.
• Recommended adjustment:
  • If certain extraction adjustments are desired, slightly modifying pouring height can help fine-tune extraction.
  • Maintain moderation to avoid over-extraction, ensuring even extraction and balanced flavor.

By understanding and adjusting these variables, you can consistently achieve balanced, flavorful pour-over coffee.