The Fluid Dynamics of Flavour: An Interim Forensic Audit

Published by: Coffee Analytica Lab

Investigator: H.X. Sterling, Lead Analyst

Date: January 19, 2026

I. The Core Physics: Interactive Forces in Percolation

To understand Total Dissolved Solids (TDS), we must view the pour-over dripper not as a kitchen utensil, but as a Porous Media Reactor. Our research has identified four primary forces that dictate the final concentration:

• Hydrostatic Pressure (P): The mass of water sitting above the coffee bed. Higher weights (e.g., our 100g+ pours) increase the pressure head, forcing water into particle pores. However, this carries a mechanical trade-off: excessive pressure can trigger bed compaction, reducing permeability.

• Dynamic Viscosity (μ): This is the fluid's resistance to flow, which is heavily temperature-dependent. We observed that as the slurry temperature drops - due to ambient air or cold dripper walls - the viscosity increases. This naturally slows the draw-down velocity, extending contact time and shifting the extraction profile.

• Hydraulic Conductivity (k): The ease with which water passes through the coffee-paper matrix, governed by Darcy’s Law. We discovered that a "finer" grind is not a linear path to higher extraction; if conductivity is too low, "choking" occurs. This creates high-resistance zones that force water into bypass flow, ultimately lowering TDS.

• Diffusion Gradient: The concentration delta between the solute-rich interior of the coffee particle and the surrounding solvent. By utilizing Brita-filtered water to manage mineral content, we maintain a high gradient, allowing the water to strip solubles more efficiently than "saturated" tap water.

II. Proven Hypotheses: The Coffee Analytica Breakthroughs

1. The Gaseous Displacement Barrier

The Proof: In session 20260116_001, we observed that a heavy initial pour (81.9g) led to a significant TDS drop (1.11%).

The Science: Coffee is a gas-solid-liquid system. During the first pour, CO₂ is still exiting the particles. A heavy volume of water at this stage cannot penetrate the particle cores because the escaping gas acts as a physical shield. The water simply "slips" past the particles, resulting in a high-volume, low-extraction event.

2. The Hydraulic Choking Point

The Proof: Moving from 60 clicks to 65 clicks on the KINGrinder K6 increased TDS from 1.20% to 1.25%.

The Science: Counter-intuitively, a coarser grind can extract more efficiently. At 60 clicks, the particles were so tightly packed they created Micro-Channelling - water found a few fast paths and ignored the rest of the bed. At 65 clicks, the bed "opened up," allowing uniform flux and total bed saturation.

3. The Thermal Bias of Instrumentation

The Proof: A single batch measured 1.31% at 28.5°C and 1.15% at 25.4°C.

The Science: Consumer TDS meters suffer from non-linear Automatic Temperature Compensation (ATC) error. For forensic-grade data, samples must be measured at room-temperature equilibrium (~25°C) to neutralize ionic mobility bias.

III. Un-concluded Variables (The "Gray Data")

While our data logs are robust, two specific variables remain in the "analytical gray zone":

1. Filter Surface Area vs. Porosity: We proved the Hario V01 media is faster than the V02, but we have yet to determine if this is due to fiber density or if the shorter physical height of the water column changes the pressure profile.

2. Agitation Vectoring: We have confirmed that pour velocity matters. However, we have not yet quantified the mathematical difference in extraction efficiency between Vertical Agitation (kinetic energy from height) vs. Centrifugal Agitation (vortex-driven turbulence).

IV. Future Research Roadmap

To move toward a complete predictive model of coffee extraction, the Research Lab will focus on the following milestones:

• The "Micro-Bloom" Study: Testing if a smaller, more controlled bloom (e.g., 20g) followed by an extended 2-minute degassing phase completely eliminates the Gaseous Barrier.

• 70-Click Sensitivity Test: Identifying the "Efficiency Cliff" - the point where coarseness finally causes TDS to drop due to the loss of total surface area.

• Water Ion Drift: A longitudinal 30-day study on Brita filter effectiveness to map how "Filter Age" shifts the flavour baseline from Fruity/Acidic to Caramel/Sweet.