Buzz
Charcoal is produced by exposing wood to high heat without oxygen.
Kim Steele/Getty ImagesMain Takeaways
- Smoke generated by a fire comes from the evaporation of volatile organic compounds within the wood as it heats up.
- As these compounds reach a certain temperature, they catch fire, transforming into carbon dioxide and water vapor, which causes the smoke to vanish, as these byproducts are not visible.
- Charcoal, created by heating wood without oxygen, burns pure carbon, producing carbon dioxide and leaving minerals behind as ash. This is why charcoal fires do not emit smoke.
Imagine a cozy fire that has burned down to glowing embers. The fire still radiates heat, but no smoke is produced. You could have reached this stage using logs in a fireplace or with charcoal. If you add a piece of wood or a sheet of paper to this fire, you’ll see a cloud of smoke as it begins to heat. Then, often with a small pop, it bursts into flame, and the smoke disappears.
If you've ever had a fireplace, wood stove, or been around a campfire, you're probably familiar with this little scene. It reveals a lot about smoke, so let's take a closer look at what's going on.
There are four key components present in every piece of wood:
- Water - Freshly cut wood is packed with water, sometimes comprising more than half of its weight. Seasoned wood, or wood that's been left to sit for a year or two, has significantly less water, though it still contains some.
- Volatile Organic Compounds - While the tree was alive, it stored sap and a range of volatile hydrocarbons in its cells. As explained in How Food Works, cellulose, the main component of wood, is a carbohydrate composed of glucose. A volatile compound is one that evaporates when heated. These compounds are flammable (similar to how gasoline and alcohol, both hydrocarbons, burn). The volatile hydrocarbons in wood burn in the same way.
- Carbon
- Ash - Ash consists of the non-burnable minerals in the tree's cells, such as calcium, potassium, and magnesium.
When you place fresh wood or paper on a hot fire, the visible smoke is actually the volatile hydrocarbons evaporating from the wood. These compounds begin vaporizing at about 300 degrees F (149 degrees Celsius). If the temperature rises high enough, they combust into flames. Once they ignite, there’s no visible smoke because the hydrocarbons turn into carbon dioxide and water—both invisible substances—when burned.
This is why a charcoal fire (or a fire that has burned down to embers) doesn't produce smoke. Charcoal is made by heating wood to very high temperatures in an oxygen-free environment. The wood is placed in a sealed box made of steel or clay and heated to around 1,000 degrees F (538 C). This process removes all volatile organic compounds, leaving only carbon and minerals (ash). When you light the charcoal, it's the pure carbon that burns, combining with oxygen to form carbon dioxide, leaving behind only the ash—the minerals.
Coke from coal is essentially the same process. Coke is coal that has been heated in an oxygen-free environment to remove the volatile components. The smoke produced during this process is quite valuable, as it contains coal tar, coal gas, alcohols, formaldehyde, and ammonia, among other compounds. All of these can be extracted from the smoke through distillation. You may have heard of methanol (a type of alcohol) referred to as "wood alcohol"—this substance was once made by distilling it from wood smoke.
