How to Measure Chocolate Particle Size: Grindometer Guide

A grindometer can make batch comparisons more useful than a refining clock alone. It cannot certify that every particle is smaller than its reading, nor decide whether a chocolate tastes finished. The important distinction is between a practical coarse-particle check and a laboratory particle-size distribution.

What a Grindometer Measures

The block has one or more grooves that become shallower along their length. As a scraper draws a suspension over them, coarse particles or aggregates can protrude and leave visible marks. The specified pattern is read against the depth scale.

That makes it useful for monitoring the coarse end of a dispersion. It does not identify every individual particle or tell you how much material lies at each size. A few marks can also reflect contamination, agglomeration or technique. HORIBA’s chocolate measurement note distinguishes this gauge check from laser diffraction and image analysis.

D90 is different. In a volume-based laser-diffraction result, Dv90 is the size below which 90% of the measured particle volume falls. It does not mean 90% of particles by count lie inside a narrow interval. A mean, a D90 and a grind-gauge reading are not interchangeable specifications.

Why There Is No Universal Smoothness Number

“Thirty microns” is a useful shorthand in chocolate discussions, but not a biological switch. Particle concentration, distribution, shape, the surrounding chocolate and the person tasting it all matter.

In Breen and colleagues’ sensory study, participants could distinguish grittiness differences between chocolates with particle-size values below 30 µm; sensitivity varied between people. That was a comparison between samples, not a universal absolute detection limit.

A separate study by De Pelsmaeker and colleagues found its trained panel rated the approximately 60 µm Dv90 chocolate grainier than the approximately 30 and 40 µm versions. Its limited set of formulations and tasters does not establish a new threshold for every chocolate either.

Consequently, neither “10–20 µm is always optimal” nor “below 10 µm is always gummy” is a reliable stop rule. Excessive refining can change flow and texture, but a low gauge reading alone does not diagnose it. If a batch is thick, use the viscosity troubleshooting guide alongside its formulation and processing record.

The illustration below shows how a particle can leave a trace in a narrowing groove. An isolated trace is not the complete pattern used to report a standardized gauge result.

Choose the Gauge for the Job

TQC Sheen and other manufacturers sell several ranges, groove formats and scales. “Hegman” is a scale designation, not a synonym for micrometers; check which markings you are reading. A broad-range gauge can help with coarse material, while a finer range offers different graduations near the intended endpoint. Do not report precision that the selected instrument and method cannot support.

The TQC Sheen product information lists the available configurations. Check the exact model, calibration documentation, scraper and suitability for your food-testing procedure before buying. The existing TQC 0–100 micron affiliate listing is a shopping link, not verification of the seller’s current stock, price or calibration.

Make a Repeatable Drawdown

Use the instructions supplied with your particular gauge. For TQC’s documented method, the key steps are:

1. Clean the block and scraper, then place the gauge on a stable, level surface. Use a representative, well-mixed sample that is sufficiently fluid; standardize sample handling and temperature between checks.
2. Load enough material at the deep end to fill the groove during the draw. Pull the scraper toward the shallow end at a steady speed, maintaining contact with the gauge.
3. Inspect promptly under consistent lighting and the specified viewing angle. Follow the manual’s pattern criterion rather than choosing the first isolated scratch.
4. Repeat with fresh material and record the individual results, method and gauge range.

TQC’s manual describes reading the upper boundary of a 3 mm band containing 5–10 particles, then averaging three tests. Follow the applicable method for your instrument; do not substitute that criterion blindly for a different gauge or standard.

The sample must flow consistently, but “above 40°C” is not a universal measurement requirement. Do not add water to make chocolate flow or return a tested sample to the food batch. Keep food-test handling separate from coatings-laboratory cleaning practices.

Interpret Readings Against Your Own Specification

A result around 25 µm means that the observed pattern met your reading criterion near that groove depth. It does not prove that the batch has no larger particles or that its D90 is 25 µm.

If a reading changes unexpectedly, repeat the draw and check sampling, residue, scraper condition and temperature before extending a run. Compare consistent results with retained samples of chocolate whose finished texture you like. For a distribution-based specification, use an appropriate laboratory method rather than converting the gauge number by guesswork.

Use Time as a Log, Not a Conversion Table

Batch size, ingredients, equipment, loading, fat content and operating conditions affect refining. More fat changes the mass’s flow and grinding behavior; it does not guarantee faster particle reduction. Country of origin is not enough to assign a bean lot a fixed fat content or finishing time.

Check at intervals suitable for your machine and process, record what changed, and sample more closely as you approach a familiar endpoint. A history of similar batches can guide when to check; it does not replace checking the current batch.

Refining and flavor development are related but separate decisions. Continued processing can alter aroma, moisture and flow even when a gauge result changes little. It may also continue refining, so do not assume an ordinary melanger has switched to a size-neutral conching phase. See the conching guide and melanger refining guide for the wider process.

Clean and Protect the Instrument

Residue, corrosion and damaged edges compromise repeatability. Clean promptly using the instrument maker’s suitable method, dry thoroughly, inspect for wear and protect the precision surfaces in storage. Do not scrape hardened residue with a metal implement or use an abrasive pad.

The Elcometer instructions specify solvent cleaning and corrosion protection for their gauges. A coatings manual’s solvent or storage oil should not be treated as permission to contaminate food: use a documented food-testing cleaning procedure and remove residues before the next test. A dry wipe alone may not adequately clean the groove.