Ahmed runs a coal station in a Dubai lounge. He is extremely familiar with the coal preparation process. He loads the burner, waits for six minutes, uses tongs to take the burning coals, and places them into bowls. His workflow is very efficient but he has one frust preventionrating problem that still occurs. After placing the coals into the burner, he pulls the coals. Two or three of the coals are bright orange and are covered with a gray ash layer. However, when he checks the other side, they have turned black and are completely cold.

Ahmed has done a lot to try to fix the issue. He has even tried rearranging the coals and increasing the burn time to the max. On occasion, the coals come out perfectly that they are completely lit. Other times, every other batch is lit perfectly, and some are cold.

If this issue is familiar to you, you are not the only one. The issue of black-bottomed coals is a very common issue with hookah coal preparation. The issue can not be blamed on the coal brand, and typically is not a burner’s issue. The problem is with oxygen flow, the distribution of heat, and the timing of the coal preparation process.

In this guide, we describe the science behind why charcoal cubes have a black bottom. We also describe how to remedy this issue. Luckily, it can be fixed using a quick two-second technique per batch.

Why the black bottom?

To come up with a suitable answer, we first need to understand how a charcoal cube burns.

For a charcoal cube to burn fully, it requires 3 things:

1. Heat – the temperature to bring the cube to a state of boiling.
2. Fuel – the cube itself which provides the fuel in the form of carbon (sufficient fuel)
3. oxygen – fresh air that needs to be in contact with the burning surface.

When you place a charcoal cube on a burner coil, heat moves from the burner coil into the bottom part of the charcoal cube. This heat moves through the cube via conduction. The upper part of the cube absorbs heat the most because thermal energy tends to move upwards. The bottom part of the cube, which is in contact with the burner coil, does not have any air. The upper part of the cube gets in contact with the open air, which means that air (oxygen) can get in contact with it. This means that the top of the cube, which is not in contact with the burner coil, is able to experience combustion.

The Oxygen Starvation Problem

The cube is in contact with air at the top and most of the sides. This means that air (oxygen) can get to thookah hoses parts, which experience combustion, thus producing the orange glow and creating ash.

Now look at the bottom. The bottom surface of the cube is in direct contact (almost touching) with the metal coil of the burner or the heating plate. Air cannot easily reach the bottom surface of the heating coil. The coil can heat the bottom of the cube to a high temperature, but without oxygen, combustion cannot happen. The carbon at the bottom can’t fully heat to several hundred degrees, but stays black because no oxygen is supplied to continue combustion.

This is also why a log in a fireplace will turn black on the side resting on the grate. The side that is exposed to air burns. The side that is pressed against the grate starves for oxygen and stays dark.

Why this is Important with Lounge Service

A black-bottomed coal is an indication of that coal is only partially lit. The black side, when resting on a bowl, becomes a heat sink. This side absorbs heat from other parts of the coal and does not transfer heat to the tobacco. The implications of this are:

• Longer session time as the bowl heats up
• The coal may extinguish within 15 to 20 minutes, resulting in the need to replace the coal.
• There coal produces a bad, toxic taste

For lounges that run around fifty or more coal sessions per night, black-bottomed coals can become a significant problem. One table runs a perfect session, and the next table runs a session that dies after 20 minutes. The customer is never satisfied and thinks the tobacco is bad when really the problem is the coal.

 The Four Main Causes of Black-bottomed Coals

Oxygen starvation is the primary issue, but there are four other contributing causes that can produce black-bottomed coals.

1. Overcrowding the Burner

Busy lounges often face this issue. To save time, staff try to light as many coals as possible. This ends up being nine, ten or sometimes twelve 25 mm cubes on a burner designed to heat six to eight at a time.

As you pack more cubes together, their corners touch. When their corners touch, the surfaces lose exposure to the airflow. This makes things worse. Rather than having one surface touch the coil, multiple surfaces touch other cubes. The result is multiple cubes leaving the burner with blackened spots on the sides and bottoms.

2. Dirty or Warped Burner Coils

After prolonged use, dust from charcoal, carbon, and ash build up on the burner coil and the metal plate under the coil. This forms a layer that insulates the coil from the cube. Although some heat is still conducted, the bottom of the cube gets less heat; eventually, it gets enough to ignite, but the oxygen starvation problem still exists.

Also, burner coils can bend out of shape after prolonged use. A bent coil leads to uneven interaction with the cubes. Some cubes are further away from the coil, meaning heat is conducted less. Other cubes are pressed against the coil, meaning more heat is conducted. Nevertheless, airflow around the cube is reduced.

3. Using Coals That Are Too Large

Bigger cubes (26 mm or 27 mm) have a larger thermal mass than the standard 25 mm cubes. Also, having a larger size means having a smaller surface area relative to the total volume. This means a bigger cube takes longer to heat through, and the bottom surface that is touching the coil receives inadequate airflow for a longer duration.

A 27 mm cube’s volume is approximately 25% greater than that of a 25 mm cube. But, its surface area is only about 10% greater. The extra mass in the interior helps delay the heating of the bottom surface to reach the combustion temperature, and therefore, makes it more difficult for combustion to occur at the bottom.

 4. Insufficient Pre-Heating Time

Some burners take longer to reach their full operating temperature than do others. Hence, if you load coals onto a burner that is not fully hot, the initial heat transfer is less than the desired value. The bottom of the cube slowly begins to heat, and by the time the top of the cube is glowing, the bottom of the cube may never reach the combustion temperature.

This effect is most pronounced with burners that have automatic shutoff features or temperature cycling features. For instance, if the burner cycles off because it has reached the set temperature, and you load fresh coals, the burner may not immediately turn back on.

Solution: The Flip-and-Finish Technique

Black bottoms are caused by the reasons discussed earlier, and this technique is the practical solution that can eliminate the problem in almost all the cases.

Step 1: Standard Lighting (6–8 Minutes)

Place the coals on the preheated burner. Allow the coals to heat for 6 to 8 minutes (depending on your burner wattage and coal size), at this stage, the top and sides of each cube should be glowing orange with a light gray ash coating, while the bottom will still be fully or partially black.

step 2 – coal flipping

With your tongs, flip the coal over so the black bottom is now facing up. You are not rearranging the coals. This allows the previously starved bottom surface to have access to air.

Flipping a batch of eight coals only takes 10 seconds. Time-wise, it slows down the flow of work, because you would pick the coals up with tongs anyway. You have to flip them before you transfer them.

step 3 – let the bottom catch (1-2 minutes)

After flipping, let the coal sit on the burner for 1-2 minutes. With the black surface now exposed, the surface can glow. Within 30-60 seconds, it can begin to glow orange. Within 2 minutes, the coals are lit.

step 4 – transfer to the bowl

Pick up each coal and place it in the bowl or HMD. Each coal is now fully lit. During a session, the coal changes, the coals burn down faster, and there is a thick vapor with the first pull.

Why This Works

Two-part coal lighting requires heat and oxygen. The flip-and-finish method is structured like this:

1. The bottom side of the coal contacts the heat source. This takes 6-8 minutes.
2. The coal is flipped. This provides oxygen and takes 1-2 minutes.

This method ensures all sides of all coal cubes get enough heat and oxygen.

Variation for High-Volume Workflows

If you’re at a high-volume lounge and 2 extra minutes is impossible, you can use a quicker method. As you place the coal on the bowl, flip it and check the bottom. If it’s black, hold it suspended for 15-20 seconds. Doing this should provide enough oxygen to allow the coal’s bottom to catch flame.

This method actually takes the same amount of time as placing it directly, it just changes the motion.

Preventing Black Bottoms Before They Happen

Outside of using the flip-and-finish technique, you can also optimize your tools and methods to reduce black-bottomed coals.

Selecting a good burner

Heat inconsistency is the drawback with many burners. An electric charcoal burner for hookah with a coiled burner that is well-designed heats each cube fully avoiding too hot or cold zones. The following should be incorporated in the design:

• – Flat heating surface that is fully level.
• – At least 1,200 W for heating.
• – A heating element that can be replaced.

Use quality tongs

The perfect tongs allow for fast and safe coal flipping. But if a tongs are thin and poorly balanced, flipping coal becomes a time wasting mess. A pair of stainless steel tongs with a consistent grip and a handle designed to be ergonomic allows for flipping of a full batch in under 10 seconds while keeping all coals perfectly intact.

Add preheating to the to-do list

Preheating should be added to the to-do list. Just turn the burner on as soon as you get to the shift that you are running. By the time you are loading the first batch the burner has been up to full power for a few minutes.

Change the Positon of the Burner

Use a technique that involves marking the hot spots and coal batches in the areas of the coil that are running hot. You should be flipping the batches to ensure all areas or coal batches received the same heating. This technique is particularly effective during long shifts to reduce the effect of cold batches that run continuously.

Monitor Airflow Around the Burner

The burner has specific demands for airflow. Coal burner stations that are cramped into corners with poor ventilation will likely cause the ambient oxygen level to drop around the burner. When coal is placed on the burner, then air will be contested for, further worsening the oxygen starvation around the coal burner. To minimize this issue, place your burner in an open area with good airflow, or add a small fan to the coal burner that will ensure a fresh supply of air to the burner and coal.

When It Is Not the Flipping: Ruling Out Other Problems

Black-bottomed coals can also be due to other causes. If the flip-and-finish technique is not correcting the issue, review the following potential causes.

Low-Quality Charcoal

Cheap coconut charcoal often contains binding agents that can lead to inconsistent carbonization. Coals with this carbonization can lead to uneven heating from the bottom surface to the top. As a result, the bottom surface will be hot enough to blacken, but the internal structure lacks the heat necessary to sustain combustion and react with the oxygen that is provided.

To determine if this is the case with your charcoal, try to light a single cube on its own away from other coals. If the hookah bases remains black after a 10 minute duration, the issue is with the coal.

Moisture in the Charcoal

The porous nature of coconut charcoal allows them to absorb moisture from the air. When the humidity is high, the charcoal can absorb a significant amount of moisture supply, which can hinder the lighting of the coal. When heated, the moisture in the coal converts to steam which takes the space that is occupied by oxygen, and also the coal’s surface. This prevents combustion entirely.

Store your charcoal in sealed containers in a dry location. If you think they may have absorbed moisture, try drying some in a low oven (150°F / 65°C) for 30 minutes as a moisture test.

Inconsistent Power/Heat from Burners

If your burner is plugged into a circuit shared with other appliances that use a lot of power (like refrigerators, ice machines, other burners, etc.), then the effective power of the burner is likely to be diminished due to voltage drops. Your burner may feel hot to the touch, but due to this loss of power, it may be putting out less heat than its rated wattage. As a result, the bottom of the burner is kept below its combustion temperature.

The solution is to plug your burner into a dedicated circuit or use a voltage stabilizer.

Create a Standard Operating Procedure (SOP) for Your Lounge

The best way to ensure that staff never allow black-bottomed coals is to make it part of their standard standard operating procedures. Below is a simple SOP that your staff should follow each shift.

Coal Station SOP

1. Set burner to max. Preheat for 3 minutes.
2. Ensure the burner coil is clean, flat, and brush off any debris.
3. Ensure tongs are within easy reach.
4. Load 6–8 cubes max.
5. Set burner to 6 minute timer.
6. Flip each coal to show the bottom side with tongs once the timer has gone off.
7. Set to 2 minute timer.
8. Ensure each side of all coals are glowing. (If not, they are not ready to be served).
9. Serve coals in a tray or bowl.
10. Unplug burner.
11. Let burner cool completely.
12. Empty ash tray.
13. Clean the coil surface with a brush.
14. Store tongs and accessories in the designated spot.

The order in which the steps are carried out in this SOP takes around 8 minutes in total. This is about the same length of time as any other standard method for lighting coals. This method ensures your coals are fully lit on the outside and every other side every time.

Conclusion

There is nothing mysterious about black-bottomed charcoal cubes. No, they are not the sign of irregular charcoal or a faulty burner. They result from the natural oxygen starvation of the surface that is pressed against the heating coil. The answer is to flip the coals to expose the bottom side to air for the last 1 or 2 minutes.

After reading this, Ahmed was the first to put the flip-and-finish method into practice at Cairo Lounge. After the first night, his staff complained the step added unnecessary time to the lighting process. By the third night, it had already become habitual. Within a week, the complaints about short sessions and inconsistent smoke dropped by 80%. The coal station became the most reliable and predictable part of his operation.

You can solve the problem of black-bottomed coals without buying extra equipment. You just need a pair of tongs, 10 seconds more than normal, and a better understanding of what is happening inside the cube. Use the right tools, like electric charcoal burners, stainless steel tongs, and heat management devices. Then every coal that leaves your station will be fully lit and every step will allow your customers to have a perfect session.