Filter permeability and resistance

How the physical properties of coffee filters affect water flow, extraction, and cup quality.

Article 8 of 12 in Brewing Physics & Extraction Theory/

Filter Permeability and Resistance

Permeability:
Defines how easily water passes through the filter material.
Higher permeability allows faster flow, potentially reducing extraction.
Lower permeability slows flow, increasing contact time and extraction.
Filter Material Types:
Paper: Provides high resistance; traps fine particles; may absorb oils affecting body.
Metal: Lower resistance; allows more oils and fines into cup; can increase body and flavor complexity.
Cloth / Mesh: Medium resistance; reusable; balances clarity and body.
Thickness & Density:
Thicker or denser filters increase flow resistance.
Impacts brew time, extraction yield, and clarity.
Channeling & Bed Compaction:
Uneven coffee bed or filter wrinkles can create low-resistance channels.
Channeling leads to under-extraction in some areas and over-extraction in others.
Method-Specific Considerations:
Pour-over: balance filter resistance with grind size to control flow rate.
Espresso: use filter baskets designed for consistent resistance under pressure.
Cold brew: coarser grind and filter choice influence extraction efficiency.
Practical Tips:
Always pre-wet paper filters to minimize paper taste and ensure even water flow.
Monitor flow rate and adjust grind or tamping to compensate for filter resistance.
Understand filter resistance as part of overall extraction control for consistent flavor and strength.