Drying and moisture control

By Mohamad Sinno, Charcoal Expert · published 7 September 2026. Not reviewed by the Head of QC — the reviewer byline on our older production pages carries the date those pages were read, and this one has not been read yet.

Drying is the longest stage in this process by a wide margin, and the one whose result a customer feels first — in how a piece lights, whether it spits, and whether it cracks under heat. It is also where the market's published figures diverge most sharply from ours.

The short answer

A briquette leaves the press wet and has to lose most of that water without losing its structure. Dry the surface much faster than the core and you build internal stress; go slowly enough and you spend days on it. Every drying method is a position on that trade, and the figure a buyer is quoted usually does not say which moment it was measured at.

Ours, stated with its dates

Those two numbers must not be mixed, and there is a third that is neither of them. The grade ceilings in a specification are a maximum a product may not exceed — not a stage target and not a measured result. So a "≤8% moisture" figure circulating as though it described what a dryer aims for is a ceiling being read as a target, which is the commonest confusion on this parameter. The three, kept apart:

The measured samples and the packing target are not reconciled here, deliberately — that distinction is worked through on the moisture page.

A window that does not reconcile with ours

A producer publishes the clearest account of drying physics on this SERP, and its recommended oven window is nowhere near ours. Its mechanism first, because it is genuinely useful: "When the surface dries significantly faster than the interior, a large moisture gradient develops across the briquette cross-section. The dry surface material shrinks as moisture leaves it. The wet interior does not shrink at the same rate… This differential shrinkage creates internal stress… When that stress exceeds the tensile strength of the material at any point, a micro-crack forms."

Its prescription: "Correctly operated oven drying — controlled temperature of 60-80°C, moderate airflow velocity, sufficient dwell time — produces the most uniform moisture gradient of any drying method and the lowest micro-crack risk", with a hybrid route taking pieces to an intermediate level in an oven and finishing in ambient air (omnicococharcoal.co.id, 29 May 2026).

Set that beside our 160 °C and the two do not average into a convention. We are not going to split the difference or explain their figure away, and we are not claiming their window is wrong. What we can say is what each is: theirs is a published recommendation from a producer describing its own practice, dated; ours is a confirmed first-party parameter with a stated dwell time of 75 to 85 hours — a long, slow hold rather than a short hot one, which is a different way of managing the same gradient. The honest position is that the market has no agreed drying temperature, and anyone presenting one has picked a source.

A second producer names the three methods in use — natural sun-drying, industrial ovens and controlled drying rooms — and adds the failure mode at the other end: "the process is adjusted to prevent over-drying, which can make briquettes brittle", with "Cracked briquettes are removed before packaging" (bintangbriquettes.com, 28 July 2025). And an equipment vendor puts moisture at roughly a third of mass straight out of the press, noting that even "under the scorching sun, it takes 3-5 days to dry the briquettes completely" (charcoalmachinery.com, 10 March 2026 — a product page for a dryer it sells).

The drying curve we do not publish

The obvious thing to put here is a dated drying curve from our own production records — moisture against hours, one real run. The drying log and the container loading log are not published, and no sample page of either has been supplied. So there is no curve to show, and a plausible one drawn to fit the figures above would be an illustration presented as a record.

What is recorded is the sampling. Drying is one of the 6 stages where pieces are pulled at random, at least five pieces per 50 kg, with weight, ash content, moisture, ash colour noted each time, and moisture is the parameter that matters at this one. Per batch the file holds ash content, moisture, burning time, drop test, cracks, temperature — cracks among them, which is the symptom this stage causes when it goes wrong. The checkpoint list is here.

What it produced, measured

Three samples, tested by one laboratory. They are not a specification and not a promise about your container — and we are not going to explain how they relate to the packing target, because nothing we hold connects the two events.

Your own reading takes an oven and a scale: drying oven at 120 °c for 5–10 minutes, weighing before and after. That is a quick check rather than the constant-mass method, and it is enough to compare cartons against each other and against the certificate for that batch.

Holding it from the oven to the vessel

Drying decides a number; the weeks afterwards decide whether you receive it. Between the oven and your warehouse the piece sits through a weathering hold, is packed on a day whose temperature is recorded, and travels enclosed in a thermal blanket inside a vacuum-sealed load, with headspace between cargo and container ceiling and a gap at the door.

That is a practice rather than a record — there is no voyage moisture log either, for the same reason there is no drying curve. What it protects against is the mechanism above running in reverse: a dry piece in a humid container takes water back, and takes it back at the surface first. Sparking on ignition is the usual first symptom, and it is diagnosed on the sparking page.