Conching: what those hours are actually doing

Conching is usually described as one operation but does two distinct jobs. In the dry phase the mass is thick and is worked under shear and heat; acetic acid and other harsh volatiles drive off, and flavour continues to develop through further Maillard chemistry.

In the liquid phase, cocoa butter and usually lecithin are added and the mass becomes fluid. Here the work is physical: coating every solid particle in fat so the chocolate flows properly and feels smooth.

Conch times range from a few hours to several days, and the range reflects the beans as much as the style. A harsh, acidic lot needs a long dry conch. A well-fermented, well-roasted lot may need very little.

Craft makers using a melangeur often conch and grind simultaneously — the prolonged shear does much of the same work — which is why a melangeur-only process can produce good chocolate without a separate conch at all.

The volatiles that carry harshness also carry character. Conch a distinctive bean long enough and you get a smooth, clean, characterless chocolate — which is precisely what much mass-market chocolate is, and it is a deliberate choice rather than a failure.

This is why the length of conching correlates with smoothness and inversely with distinctiveness. Smoothness and character are traded against each other in the same machine.

Conching does not reduce particle size in any meaningful way — that is refining's job, done before conching by roll refiners or ball mills. The two are constantly conflated.

It also cannot fix bad beans. Smoke taint, mould and under-fermentation all survive any length of conching. Conching removes volatile harshness, not defects.