Modeling puck resistance over time
How the resistance of a coffee puck evolves during the brewing process, influencing flow rate and extraction dynamics.
- Coffee Basics Nerds
- 2 min read
Modeling Puck Resistance Over Time
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Dynamic Resistance:
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Coffee puck resistance is not constant; it changes as water interacts with the coffee bed.
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Early in the shot, water encounters less compaction and soluble extraction is minimal.
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As extraction progresses, soluble solids dissolve, pores may swell or clog, and resistance typically increases.
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Factors Affecting Resistance:
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Grind size and uniformity: Finer grinds increase initial resistance.
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Tamping pressure: Heavier tamping compacts the puck, raising resistance from the start.
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Water temperature: Hotter water can dissolve solubles faster, slightly altering resistance profile.
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Channeling: Uneven compaction creates low-resistance paths, lowering effective resistance in parts of the puck.
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Intuitive Visualization:
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Imagine squeezing a wet sponge: initially soft, but as water is absorbed and spaces tighten, it becomes harder to pass liquid through.
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The puck behaves similarly, with resistance rising as extraction proceeds.
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Practical Applications:
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Helps in designing espresso shots with controlled flow rate throughout the extraction.
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Guides adjustments to grind, dose, and tamp to achieve consistent puck resistance.
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Useful for predicting shot behavior in real-time and preventing under- or over-extraction.
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Experimental Tips:
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Track flow rate vs. time on a scale or with sensors to visualize resistance changes.
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Compare shots with different grind settings to see how resistance curves shift.
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Use modeling to refine shot parameters for consistency across different beans or roasts.