Ash content, burn time and shape: shisha charcoal specs explained
Key points
- Ash content, fixed carbon and moisture are measured in a lab. Burn time, smell and ash behaviour are tested on a bowl.
- Typical coconut shisha cube targets: 72 to 76% fixed carbon, ash max 2.5%, moisture max 5%, 60 to 90 minutes burn.
- Shape changes density, heat curve and the number of pieces per kilo, not only the look of the box.
- Write the test method into the contract so factory, inspector and buyer measure the same thing.
A shisha charcoal spec sheet is short, usually five to eight lines. Each line hides a lot of detail about how the charcoal was made and how it will behave in a lounge. This guide explains every value that appears on a typical coconut shisha spec, what drives it and how to check it on samples before you order a container.
If you are new to sourcing from Vietnam, start with our buyer’s guide to coconut charcoal from Vietnam and come back here for the detail.
The typical spec sheet
| Parameter | Shisha cube | Hexagonal shisha | How it is measured |
|---|---|---|---|
| Fixed carbon | 72 to 76% | 74 to 78% | Lab, proximate analysis |
| Ash content | max 2.5% | max 2.0% | Lab, proximate analysis |
| Moisture | max 5% | max 5% | Lab, oven drying |
| Volatile matter | the balance, often 15 to 20% | the balance, often 14 to 18% | Lab, proximate analysis |
| Density | not always stated | 1.05 to 1.15 g/cm³ | Weight and volume |
| Burn time | 60 to 90 min | 80 to 110 min | Bowl test |
| Size | 25 or 26 mm cube | Per die | Caliper |
The first four values are the proximate analysis. They add up: moisture, volatile matter, ash and fixed carbon together make 100% of the sample. When one goes up, another must come down. That is why a factory cannot promise very high fixed carbon and very high volatile matter at the same time.
Fixed carbon
Fixed carbon is what remains after moisture, volatiles and ash are removed. It is the part that burns slowly and steadily on the bowl. Higher fixed carbon means more usable heat per cube and a longer, more even session.
Fixed carbon depends mainly on carbonisation. Shell that is carbonised at the right temperature for long enough reaches a high fixed carbon. Rushed or incomplete carbonisation leaves more volatile matter behind. Fixed carbon also drops if the factory mixes in cheaper filler to stretch expensive shell.
Some spec sheets on the market quote very high fixed carbon figures for coconut shisha. Treat any figure as a claim until a lab you choose has tested your own lot.
Ash content
Ash is the mineral residue after complete burning. For shisha smokers it is the most visible number, because ash falls onto the foil or heat management device, blocks airflow and can affect taste.
Three things push ash up:
- Contamination. Sand and soil picked up with the shells or during carbonisation in open pits.
- Binder. Too much binder, or a binder with mineral content, adds ash.
- Filler. Some low-cost cubes contain non-coconut material.
Ash colour is a quick visual check. Clean coconut charcoal usually leaves light grey to white ash that holds its shape briefly before breaking. Dark or reddish ash and a lot of fine dust are warning signs worth sending to a lab.
Moisture
Moisture is water left in the cube after drying. Factories dry pressed cubes in ovens or drying rooms until moisture falls below the target, usually 5% or less for shisha.
High moisture makes cubes hard to light, lowers burn time, causes sparking and cracking, and in the worst case leads to mould during a long sea voyage. Charcoal also absorbs humidity from the air, so a lot tested at the factory can read higher when the inspector samples it days later in a humid warehouse. Agree when the moisture sample is taken.
Volatile matter
Volatile matter is released as gas when charcoal is heated. In shisha it shows up as smoke, smell and a harsh first few minutes. Properly carbonised coconut charcoal has low volatile matter. Binder that is not fully dried also adds volatiles and a starchy smell during lighting.
Density and shape
Shape is not only about how the box looks. It changes how much charcoal fits on a bowl, how heat is distributed and how many pieces a customer gets per kilo.
| Shape | Common size | Notes |
|---|---|---|
| Cube | 25 x 25 x 25 mm or 26 x 26 x 26 mm | The standard lounge format. Hydraulic press, then cut. |
| Hexagonal | Per die, often extruded then cut | Hollow centre on some designs, higher density, distinctive look. |
| Flat | Rectangular tile | Popular with some heat management devices. |
| Finger | Long thin bar | Fast to light, shorter sessions. |
Density comes from particle size, binder ratio and pressing force. Denser pieces burn longer but can take longer to light. Hexagonal extruded pieces are often denser than pressed cubes, which is why their burn times run longer.
Burn time
Burn time is the value buyers care about most and the one that is least standardised. There is no single lab method. Two parties can both be honest and get different numbers because they tested differently.
Agree a simple protocol with the factory and the inspector, for example:
- Light three cubes on an electric coil until fully glowing on all sides.
- Place them on a standard bowl with a standard heat management setup.
- Time from placement until the cube no longer produces usable heat.
- Repeat on three samples and report the average.
Write this protocol into the contract. When burn time is disputed later, you will have a reference.
How to test samples yourself
Lab results tell you the composition. A bowl test tells you how the charcoal behaves in use. Do both. When samples arrive, run this checklist:
| Check | What to look for |
|---|---|
| Size and weight | Consistent dimensions, no chipped corners, weight per 1 kg box close to stated |
| Lighting | Time to full glow on a coil, no excessive sparking |
| Smell | No chemical or starchy smell after the first minutes |
| Smoke | Little visible smoke once lit |
| Ash | Light grey to white, low volume, does not crumble into dust instantly |
| Burn time | Measured with your protocol, averaged over several pieces |
| Breakage | Few broken pieces in the box after transport |
Compare samples from each factory side by side on the same day, with the same bowl and the same person testing. Small differences in setup make large differences in results.
Writing the spec into your contract
A good contract clause states the value, the limit and the method. For example: “Ash content max 2.5% on dry basis, tested by the buyer’s appointed inspector using ASTM D1762, sample drawn from at least ten cartons per container.” Many certificates cite the coal and coke methods ASTM D3172, D3174 and D3173 instead; either can work if both parties agree in writing.
State whether values are on an as-received or dry basis. Ash and fixed carbon on a dry basis will read higher than on an as-received basis because the water is removed first. Many disputes come from comparing numbers on different bases.
Sampling for the lab
A lab result is only as good as the sample. For a container, the inspector should draw pieces from many cartons across the load, not from one open box at the front. Agree the number of cartons sampled, how the pieces are combined and how much is sealed as a retained sample. A clear sampling rule prevents arguments later about whether the tested pieces represent the shipment.
Common pitfalls
- Comparing spec sheets, not samples. Paper specs from different factories are rarely measured the same way.
- Testing only the first lot. Spec drift often appears on the third or fourth container. Test every container.
- Ignoring breakage. A cube that meets every lab value is still a complaint if a quarter of the box arrives broken.
- No retained samples. Ask the inspector to seal and keep a reference sample from each lot in case of a later dispute.
Next step
Once you know your target values, put them in one RFQ. We match it to up to 3 Vietnamese factories that produce that grade and can meet the numbers, and we reply within 24 business hours. Send your spec or read the grade and spec guide.
FAQ
What ash content is good for shisha charcoal?
Most buyers of coconut shisha cubes ask for a maximum of 2 to 2.5% ash. Premium hexagonal lines often target 2% or below. Lower is better, but the lab method and the sample must be agreed in advance.
How long should a shisha cube burn?
A 25 mm coconut cube typically burns for 60 to 90 minutes under normal lounge use. Hexagonal pieces with higher density often reach 80 to 110 minutes. Burn time depends heavily on airflow and bowl setup.
Why does my charcoal smell or spark?
Smell usually comes from too much volatile matter or from binder that was not fully dried. Sparking and cracking point to moisture trapped inside the cube or uneven pressing.
Is a 26 mm cube better than a 25 mm cube?
Neither is better. A 26 mm cube has more mass per piece and burns slightly longer. Choose the size your lounges and customers already use.