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There is no World's Strongest Coffee by James Hoffmann

The Four Meanings of "Strength"​

Most people use the word "strength" to describe a quality of coffee, but only one definition is technically correct:

1. Caffeine Content 💊​

Many companies selling the "strongest coffee" are referring to caffeine content. They typically use Robusta coffee beans, which have, on average, twice the caffeine of Arabica beans. However, caffeine solubility means that the final amount in your cup is also affected by how you brew (e.g., longer steep times extract more caffeine).

2. Roast Level 🎨​

On supermarket coffee bags, a numerical "strength rating" (e.g., Strength 5) is often used as a shorthand for roast level. A Strength 5 indicates a dark roast, while a Strength 2 indicates a light roast. This has nothing to do with the true definition of strength.

3. Intensity of Bitterness 🔥​

A common, informal use of "strong" is to describe a coffee that is intensely bitter, harsh, or tastes burnt . This is often a result of a dark roast, which increases bitterness compounds. While it communicates a preference, it is an inaccurate use of the term.

4. Technical Strength (TDS) ✅​

The true, correct, and technical definition of coffee strength refers to the concentration of dissolved coffee solids in the beverage.

  • It answers the question: "How much of this cup is water and how much is dissolved ground coffee?".
  • This percentage is called Total Dissolved Solids (TDS).
  • A typical filter coffee is 1% to 1.5% strength.
  • Espresso is much higher, typically 8% to 12% strength.

Measuring Strength and Calculating Extraction​

Measuring the technical strength (TDS) is the critical first step to calculating extraction, which is the percentage of flavor and other compounds removed from the original ground coffee.

How to Measure Technical Strength​

You measure a coffee's strength using a refractometer. * The device measures the refractive index of the liquid, applies an algorithm specific to coffee, and outputs the TDS as a percentage.

Strength vs. Extraction​

Strength on its own is a matter of personal preference, but when combined with other data, it reveals the extraction yield.

  • Extraction is the percentage of the dry coffee grounds that ended up dissolved in your cup.
  • Example: If you start with 40g of dry coffee and 7.6g of dissolved solids end up in your cup, your extraction is $7.6g / 40g = 19\%$ .
  • Historically, the ideal range for extraction was considered 18% to 22%. Achieving this range while maintaining a preferred strength is the key to brewing delicious coffee.
  • This relationship is plotted on the Coffee Brewing Control Chart. By understanding your TDS and extraction, you can make precise adjustments (like grinding finer or coarser) to improve flavour.