Granulometry & Hygiene: Managing the Particle Spectrum

Grinding coffee is not just about making beans smaller; it is about creating a specific Hydraulic Resistance. When you brew coffee, water flows through the bed of grounds. The size of the particles determines how fast the water flows and how much surface area is exposed for extraction.

The Ollygrin BG702S offers “30 Precise Settings.” In the science of Granulometry (the measurement of particle size), these settings are coordinates on a spectrum of fluid dynamics. From the high resistance required for Espresso to the low resistance needed for French Press, the grinder is the control valve for your coffee’s flavor. This article explores the physics of particle size, the phenomenon of static electricity, and the hygiene of retention.

The Spectrum of Resistance: 30 Settings Explained

Why do we need 30 settings? Because extraction is non-linear. * Fine Settings (1-8): High Surface Area, Low Permeability.
* Physics: The burrs are close together. The particles are small, packing tightly. This creates high hydraulic resistance. In an espresso machine, this resistance is necessary to build 9 bars of pressure. If the particles are too coarse, the water rushes through (channeling), resulting in sour, weak coffee. * Medium Settings (9-21): Balanced Flow.
* Physics: For Drip or Pour-over, gravity is the driving force. The grind must be coarse enough to allow flow but fine enough to prolong contact time. This is the Darcy’s Law zone, where flow rate is proportional to permeability. * Coarse Settings (22-30): Low Surface Area, High Permeability.
* Physics: For French Press (Immersion), water and coffee sit together for minutes. If the grind is fine, the extraction happens too fast (bitterness) and the mesh filter clogs with silt. Coarse particles slow down the diffusion of solids, matching the long brew time.

The Ollygrin’s dial allows the user to manipulate these physical variables. A “precise” setting implies Repeatability—returning to setting 15 should produce the same particle distribution today as it did yesterday. This mechanical stability is crucial for dialing in recipes.

The Triboelectric Effect: Static and Mess

A recurring theme in grinder physics is Static Electricity. * The Mechanism: As coffee beans are pulverized, electrons are stripped from their surfaces due to friction (Triboelectric Effect). The dry coffee particles become charged. * The Consequence: Charged particles repel each other. They fly out of the bin (mess) or stick to the walls of the chute (retention).

User reviews often mention static. This is not a defect of the machine but a property of physics, exacerbated by low humidity environments. * The Fix: The “Ross Droplet Technique” (RDT). Adding a single drop of water to the beans before grinding increases the surface conductivity of the beans, dissipating the static charge before it builds up. While the machine may have anti-static materials (like conductive plastics or steel chutes), RDT is often the most effective physics-based solution.

Retention and Oxidation: The Hygiene of Freshness

Retention refers to the ground coffee that stays inside the grinder after the motor stops. * The Problem: In the chute and burr chamber, stale grounds accumulate. Coffee oils oxidize rapidly (rancidity). If 2 grams of stale coffee mix with your next 18 grams of fresh coffee, it taints the cup. * The Ollygrin Solution: The “Upper burr lift-off option” and included brush are engineering concessions to this reality.
* Dead Space: Every grinder has dead space. The ability to easily remove the upper burr allows the user to mechanically sweep out this retained coffee.
* Maintenance Protocol: Regular cleaning is not just for hygiene; it is for flavor. Removing the oxidized oils and old fines ensures that the grinder’s geometry remains true (caked coffee can throw off alignment) and the output remains fresh.

Conclusion: The Grinder as a Lab Instrument

The Ollygrin BG702S is more than a kitchen appliance; it is an instrument for controlling surface area. By offering a wide range of particle sizes via a stable conical burr set, it empowers the user to engineer their coffee extraction.
However, like any scientific instrument, it requires understanding. Managing static, cleaning retention, and matching the grind setting to the brew method are skills the user must develop. The machine provides the torque and the geometry; the user provides the logic. Together, they unlock the potential hidden within the bean.