THE PROCESS IN MOTION

How do we know a coffee has been cut?

Start the scene or choose a stage. The animation simplifies the mechanism; what follows gives the details and the available references.

▶ Play the process01A pinch on cold water02Under the microscope, the root gives itself away03Near infrared does the sorting04Reference chemistry confirms05NMR classifies

A pinch on cold water

Thurber, in 1881, brings detection within reach of a kitchen. On a glass of cold water, ground coffee, being oily, floats for a long time and colors almost nothing; chicory and cereals sink quickly, chicory in brown streaks. An overroasted coffee sinks too: anything that sinks must go under the microscope.

Read the stages without animation

1. A pinch on cold waterThurber, in 1881, brings detection within reach of a kitchen. On a glass of cold water, ground coffee, being oily, floats for a long time and colors almost nothing; chicory and cereals sink quickly, chicory in brown streaks. An overroasted coffee sinks too: anything that sinks must go under the microscope.
2. Under the microscope, the root gives itself awayChicory is a root: it carries vessels with dotted spirals, which conducted the sap, that coffee, a seed, never had. Cereals betray themselves by their starch grains. In 1851, Hassall thus found 31 samples adulterated out of 34 bought in London.
3. Near infrared does the sortingToday, the powder is illuminated and the light it sends back is read, without reagent. A portable spectrometer obtains 96.9% correct answers in qualitative mode, in a single scan of 2.54 milliseconds. But its model was built on a single arabica: it is a screen, not proof.
4. Reference chemistry confirms16-O-methylcafestol is a molecule almost exclusive to canephora, which survives roasting and instant coffee. Measured by chromatography, it is detectable from 5 mg/kg and quantifiable at 20 mg/kg, that is, less than 0.9% canephora in a “100% arabica.”
5. NMR classifiesNuclear magnetic resonance places the extract in a magnet and reads the signature each molecule leaves there. At 60 MHz, on a benchtop, about forty minutes per extract; at 600 MHz, coffees cut with barley, corn, husks, soy, rice or wheat are classified at 100%.

To remember: from the water glass to NMR, each tool sees more finely; the quick screen flags, only reference chemistry proves.

Read the full article and its sources ↓

Friedrich Accum published in London in 1820 a book with a blunt title: A Treatise on Adulterations of Food and Culinary Poisons. On the cover, the biblical phrase “there is death in the pot.” The book names the tradesmen instead of denouncing a scourge in general. That is what made both its fortune and its misfortune: a thousand copies sold in a month, and the named tradesmen went on the rampage.

The response did not address the substance. Accum left England in 1821, after a trial that was not about adulteration but about pages torn from the library of the Royal Institution. The opponent had left the country; the question itself remained whole.

Thirty years later, the matter started again from a medical journal. Thomas Wakley, founder of the Lancet, created the Analytical Sanitary Commission and entrusted it to the physician and microscopist Arthur Hill Hassall.

The first investigation, in January 1851, was on coffee. Of 34 samples bought in London, 31 contained chicory, bean flour, potato starch or roasted corn. Only the most expensive were pure, and the chicory itself was almost always adulterated.

This investigation answered a specific objection, and that is what gave it its reach. The Chancellor of the Exchequer Charles Wood had claimed that no method could tell whether a coffee contained chicory. Hassall refuted him under the microscope. Trade lost its best argument there: one does not ban what one cannot measure, and one now knew how to measure.

The report of April 26, 1851 carried out its threat and named the guilty sellers. The series continued until 1854 on more than 2,500 samples, then became the book Food and its Adulterations (1855). Hassall testified before the parliamentary committee of 1855.

en.wikipedia.org/wiki/Friedrich_Accum and en.wikipedia.org/wiki/Thomas_Wakley, accessed September 7, 2026; branchcollective.org, Fisher, Tea and Food Adulteration 1834-75; Thurber 1881, p. 163

Thurber brings detection within reach of a kitchen, in five questions put to a pinch of grounds and a glass of cold water. Does the powder clump under the fingers? Coffee stays loose, while roasted flours and roots form a lump. Does it float? Ground coffee, being oily, floats for a long time; chicory and cereals sink quickly. Does it color cold water? Coffee releases almost nothing in the cold, chicory sinks in brown streaks.

Is the infusion mucilaginous? Starchy substances are, coffee is not. Do the particles soften? Those of coffee stay firm. Ukers takes up the flotation test in the official methods of 1922, with the caveat that an overroasted coffee also sinks and that everything that sinks must be identified under the microscope.

Thurber 1881, p. 167-168; Ukers 1922, ch. XVII, p. 171; LC ch. 10

When the kitchen is no longer enough, the instrument comes in. Thurber gives plates at 140 diameters; Walsh returns to them. Chicory is a root, it contains sap-conducting vessels with dotted spirals that coffee, a seed, never had; a single vessel in the field condemns the sample. Cereals betray their presence by their starch grains, specific to each species. Ukers devotes a chapter to the microscopy of coffee and recalls that the chicory blend was one of the most common forms of adulteration.

Walsh adds the laboratory: sugar passed into the infusion, density, coloring power, and the ash test, the mineral fraction of a root that has drawn up the salts of the soil not being that of a seed; he gives the method without its thresholds. The official American methods compiled by Ukers fix the density: an extract of 10% pure coffee weighs 1.00986 at 15 °C, a chicory extract 1.02821, and the percentage of chicory is calculated by a linear formula; the refractive index goes from 1.3377 to 1.3448.

From the moment a microscope and an oven are needed to know what one is drinking, the consumer has lost the game; all that is left is to trust a name.

Thurber 1881, p. 167-168; Walsh 1894, p. 216, 220-221, 235-236; Ukers 1922, ch. XVI, p. 149-153, and ch. XVII, McGill method