The machines that make chocolate

After roasting, the bean has to be broken and the shell removed. Cracking fractures the bean; winnowing separates the pieces by weight, blowing the lighter shell away from the denser nib in an air stream.

A WINNOWER is any machine that does this, from a shop-vacuum-and-pipe arrangement to an industrial line. The traditional trade name for the combined unit is a CRACKER AND FANNER, which describes it exactly.

The job is harder than it sounds because the two fractions overlap in weight. Set the air too strong and nib is lost with the shell; too weak and shell survives into the grinder, where it will not refine and shows up as grittiness and a dry, papery note. Shell content is a specification in its own right for this reason.

The mouth detects particles above roughly twenty microns as grittiness. Everything in this stage exists to get below that.

A MELANGER — a stone wet grinder, and the standard machine for small makers — runs granite rollers over a granite bed, grinding nib and sugar together in a single vessel over many hours. It is slow, it is cheap, and because it also aerates and warms the mass it is doing part of the conching job at the same time, which is why small-batch practice often treats grinding and conching as one step.

A BALL MILL grinds by agitating hard balls in a jacketed vessel. A UNIVERSAL BALL MILL is a common mid-scale configuration. It is far faster than a melanger and does less of the conching work, so it is usually paired with a separate conche.

A ROLL REFINER passes the mass through counter-rotating rolls at decreasing gaps; the FIVE-ROLL REFINER is the industrial standard. It gives the finest control of PARTICLE SIZE DISTRIBUTION, which matters more than the maximum particle size alone: a distribution with a spread of sizes packs together better and flows with less fat than one where every particle is the same size.

This is the stage where scale genuinely changes the product, and it is the only one where it does.

Conching does three things at once: it drives off volatile acids, it coats every particle in fat, and it develops flavour through continued low-temperature reaction.

The LONGITUDINAL CONCHE is Rodolphe Lindt's original design, a granite trough with a roller pushed back and forth through the mass for many hours. It is largely historical and it is the machine that made modern chocolate possible — before it, eating chocolate was gritty and coarse.

Modern conches are rotary and vastly faster. What has not changed is what conching is for, and the persistent misconception is that longer is better. Conching removes volatiles; some of those volatiles are the fruit and floral character a fine bean was bought for. Extended conching of a distinctive bean can produce technically excellent, characterless chocolate.

Molten chocolate is a SUSPENSION — solid particles in liquid fat — not a liquid, and it does not flow like one. It has a YIELD VALUE: a force that must be exceeded before it moves at all. Below that force it behaves as a solid. Above it, its PLASTIC VISCOSITY governs how fast it flows.

Those two numbers together are what the trade means by chocolate's rheology, and the CASSON MODEL is the standard mathematical description of them. A material with a yield value that then flows is a BINGHAM PLASTIC, which chocolate approximates. Chocolate is also THIXOTROPIC — it thins under sustained shear and recovers when left alone.

This is not theory. Yield value decides whether chocolate holds a moulded detail or slumps; plastic viscosity decides whether it flows through a depositor or blocks it; both are adjusted with cocoa butter and emulsifier, and lecithin and PGPR affect them differently, which is why formulations often use both.

TEMPERING is controlled pre-crystallisation: producing a specific cocoa butter crystal form so the chocolate sets hard, glossy and snapping. A CONTINUOUS TEMPERING MACHINE does by controlled cooling and shear what tabling does by hand on a slab, and a TEMPERMETER measures the result by tracking the cooling curve of a sample. MYCRYO — powdered cocoa butter already in the stable form — does it by seeding, which is the same principle as adding tempered chocolate to untempered.

MOULDING deposits chocolate into moulds, vibrates them to release trapped air, and cools them. ONE-SHOT DEPOSITING fills shell and centre simultaneously through concentric nozzles — a genuinely clever piece of engineering that replaces the older shell-mould-fill-cap sequence.

ENROBING coats a centre by passing it under a curtain of chocolate on a belt. PANNING tumbles centres in a rotating drum while chocolate is added in layers, which is how coated nuts and dragées are made.

A COOLING TUNNEL cools the formed chocolate under controlled conditions, and it is a more common source of defects than its dullness suggests: cool too fast and the chocolate cracks or blooms, too slow and it never sets properly.

DEMOULDING is where all of it is judged. Properly tempered chocolate contracts as it sets and releases from the mould cleanly. Chocolate that sticks was not properly tempered — which makes demoulding the most useful diagnostic in the whole process, and free.