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Coconut Shell Charcoal Specifications: Ash Content, Fixed Carbon and Moisture Explained

Almost every charcoal enquiry we receive asks for the same three numbers. Here is what each one measures, how it is tested, and the trade-offs a specification sheet will not tell you.

If you buy coconut shell charcoal, your first message to a supplier probably asks for ash content, fixed carbon and moisture. Those three figures do most of the work in a purchasing decision. They are also the three most commonly overstated numbers in the trade.

This article explains what each figure means, which test method produces it, and — more usefully — where the numbers conflict with each other.

Ash content: what is left when everything burnable is gone

Ash is the mineral residue remaining after complete combustion. In coconut shell charcoal it comes from two places: minerals naturally present in the shell, and contamination picked up during handling — soil, sand, dust from an unpaved drying yard.

Ash content is measured under ASTM D3174 or a comparable standard. A sample is burned at a controlled temperature and what remains is weighed.

For shisha charcoal, buyers typically look for ash below 2.5%. Lower is generally better: ash produces a grey coating, reduces heat, and leaves residue in the bowl.

Why low ash alone is not enough

Here is what a specification sheet will not say. Ash content can be lowered by carbonising at a higher temperature, which burns off more volatile matter — but push it too far and the charcoal becomes brittle, produces more dust in transit, and lights harder. A briquette with 1.5% ash that arrives as 20% broken pieces is worse than one with 2.2% ash that arrives intact.

Ask for ash content and breakage rate together. Suppliers who only volunteer the first number are selecting which fact you get to see.

Fixed carbon: the part that actually burns long

Fixed carbon is the solid combustible material left after moisture, volatile matter and ash are accounted for. It is what produces sustained heat, and it correlates directly with burning time.

It is usually calculated rather than measured directly:

Component	Typical range	Method
Moisture	3–8%	ASTM D3173
Volatile matter	10–20%	ASTM D3175
Ash	1.5–3%	ASTM D3174
Fixed carbon	by difference	100 − the three above

Because fixed carbon is derived by difference, an inflated fixed carbon figure is often just an understated moisture figure. If the four numbers do not sum to 100, the sheet is not a real lab report.

Moisture: the number that quietly costs you money

Moisture is water held in the charcoal. It matters for three reasons, only one of which is about quality.

• You pay for it by weight. At 10% moisture, one tonne in twenty is water you have shipped across an ocean.
• It reduces heat. Energy that evaporates water is energy not heating your product.
• It invites mould. In a sealed container crossing the equator, high moisture plus temperature swings produces condensation and mould on the packaging.

Moisture below 5% is a reasonable target for briquettes. Below 3% is achievable but the charcoal becomes fragile.

How to read a specification sheet

Three practical checks before you trust any figure:

• Does it name a test method? "Ash: 1.8%" means nothing. "Ash: 1.8%, ASTM D3174" means something.
• Is it per batch or a marketing figure? A typical value is an average from a good day. A certificate of analysis is tied to the batch you are actually buying.
• Do the numbers add to 100? Moisture, volatile matter, ash and fixed carbon must sum to 100. It is surprising how often they do not.

What we do

We test every batch and send the certificate of analysis before loading, not after. If a batch misses the agreed specification, we say so before it ships. Samples are free — one kilogram, sent with the batch COA, so you can verify against your own lab rather than take our word for it.