Fire. It’s an amazing thing. It’s so amazing that the ancient Greeks considered it one of the major elements. Water, air, earth and fire. The four building blocks that make up the world. Even today, people refer to fire as a living, breathing thing. Fire is probably the most destructive force in nature. But fire, when harnessed correctly can also be one of the most beneficial. In the world of barbecue, it’s probably the most important element.
Unlike water, air and earth, fire isn’t matter. It’s a chemical reaction. A side effect if you will, of changing form. Fire is caused by a reaction of oxygen with some sort of fuel. In the case of a barbecue, that fuel is ideally wood. Now just having wood and oxygen together doesn’t automatically create fire. If it did, we’d all be in pretty bad shape. Something must heat the wood, and that can be anything from a match to lightening to friction. Oh, I remember my Boy Scout days of starting fires by rubbing two sticks together. What a pain in the ass that was!
Once the wood reaches 300 degrees Fahrenheit, the cellulose in the wood begins to break down. This decomposed cellulose releases volatile gases, aka smoke. Smoke is made up of hydrogen, carbon and oxygen. Once all that is burned off, we’re left with – char; the nonburnable remnants of the wood. The char is nearly pure carbon, and ash, which is the minerals in the wood (calcium, potassium, and so on). On the store shelves, this char is known as charcoal. Charcoal is wood that has been heated to remove all the volatile gases, leaving behind only carbon. This is why pure charcoal doesn’t produce smoke when it burns.
Now the actual burning of wood takes two stages. First up, when the wood reaches 500 degrees Fahrenheit, the atoms in the wood break apart. They combine with the oxygen forming water, carbon dioxide and all sorts of other compounds. In other words – it burns. Once the gases burn off, the char ignites. The pure carbon of the char burns much more slowly and creates most of the heat of a wood fire.
As the atoms heat up, they produce light. This process is called incandescence. Flame colors will vary depending on the temperature of the fire, and the fuel source. Variations in the flame are caused by uneven temperatures. Blue flame is the hottest. Yellow the coolest.
How many nights have I sat transfixed watching the flames shoot up? Their little point dancing between the wood – or teasing the underside of a steak without ever stopping to think why fire is pointed. Well, it’s due to gravity. All the hot gases in the flame are much hotter (and less dense) than the surrounding air, so they move upward toward lower pressure. If we were in space, without gravity, the fire would burn in a sphere. Great balls of fire anyone?
Fire is self perpetuating. It keeps the fuel at ignition temperature, so it continues to burn as long as there is fuel and oxygen around it. The flame heats any surrounding fuel so it releases gases as well. When the flame ignites the gases, the fire spreads. Sometimes you want this, sometimes you don’t.
Your job as a pitmaster is to control that flame. And once you have mastered fire control, you will have mastered the first step to outstanding barbecue.