Can a 0.03% Difference in TDS Really Change the Taste? A Real Grind Speed Test with Geisha Coffee

Contents:
1. Test Coffee & Setup
2.Why Can a Small TDS Difference Taste So Big?
3. What’s the Practical Value of Grind Speed Control? This Test Teaches Us Two Important Lessons:

Coffee enthusiasts often hear the phrase: “The numbers might be close, but the taste can be worlds apart.” This time, we’re putting it to the test — using a Geisha coffee and the Mahlkönig EK Omnia variable-speed grinder to demonstrate that even when the TDS only differs by 0.03% after changing grind speed, the flavor and mouthfeel of the two cups can be entirely different experiences.

Test Coffee & Setup

We selected Ethiopia Bench Maji Lucy Geisha G1 Natural, a coffee known for its delicate florals and vibrant fruit notes — like ginger lily, elderflower, ripe fruit, wild berry jam, and passionfruit — making it ideal for comparing high vs. low grind speeds.

Brewing Parameters:

Water temperature: 90 °C
Total water: 320 g
Bloom: 40 g for 35 seconds
Grinder: Mahlkönig EK Omnia, fixed grind size 550
Test speeds: High speed 1500 rpm vs Low speed 500 rpm

Despite the TDS difference being only 0.03% and extraction yield differing by just 0.42%, the two brews tasted dramatically different.

Why Can a Small TDS Difference Taste So Big?

Many people think of TDS as a simple concentration number and assume a 0.03% difference is negligible. But TDS only tells you how much total dissolved solids are in the brew — not what those solids are. The real impact lies in the composition of those compounds.

● Grind Speed and Its Flavor Effects: High Speed – 1500 rpm
Produces more fine powder and a wider particle distribution → Greater surface area contact between water and coffee → Extracts more volatile compounds like acids and florals → Taste: Brighter, more structured, and vibrant — ideal for highlighting the floral and fruity character of Geisha beans

● Low Speed – 500 rpm
Gentler grinding, lower heat, fewer fines → Narrower particle distribution → Releases volatile compounds more conservatively → Taste: Sweeter, mellower, soft acidity, and smoother with longer aftertaste

這正是 TDS 相近但風味完全不同 的原因：同樣是 1.3% 左右，但組成的芳香化合物比例完全改變。
This is why two brews with nearly identical TDS (~1.3%) can taste completely different — the proportions of aroma compounds are fundamentally changed.

What’s the Practical Value of Grind Speed Control? This Test Teaches Us Two Important Lessons:

1. Grind speed is a hidden flavor dial
Alongside grind size, brew ratio, and water temperature, grind speed is a powerful variable that can reveal different sides of the same coffee.

2. TDS is foundational, but sensory is everything
TDS readings help confirm you’re within a reasonable extraction range, but ultimately, your palate should decide whether the cup expresses the desired flavor.

Using Bench Maji Lucy Geisha G1 Natural as the test case: High speed delivers a bright, floral, and fruit-forward profile; low speed produces a smoother, sweeter, more mellow and a caramel-like finish, ideal for those who enjoy creamy textures. So, when exploring a coffee’s full potential, don’t just fixate on the TDS number. Try adjusting grind speed, it makes brewing more fun, expressive, and versatile, a cup of coffee can tell a good story. The magic of coffee often lies in the small, overlooked details. Next pour-over brew, switch up the speed, and see what happens. Even with a manual grinder, try turning faster or slower — you might discover surprising new dimensions in your cup.

│Further reading: The Impact of Grinder Speed on Coffee's Sweetness and Acidity

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