Elevate Your Outdoor Cooking Experience with the Bull Outdoor 21039 Side Burner

How Materials Science, Thermodynamics, and a Forgotten Physical Phenomenon Power Your Barbecue

Imagine a summer evening. A drop of acidic lemon-herb marinade splashes onto the gleaming steel surface next to your grill, sizzling for a moment before evaporating. It leaves no mark. With a firm twist and a push of a knob, a sharp click echoes, and a perfect blue flame instantly erupts from the burner. There was no match, no battery, only a simple mechanical action.

We take these moments for granted, attributing them to “good quality” or “modern convenience.” But beneath these simple events lies a hidden world of profound scientific principles. That pristine steel surface is shielded by an invisible, self-healing suit of armor. That instant flame is born from a quantified torrent of thermal energy. And that effortless spark is generated by a crystal that breathes lightning. This isn’t the magic of the backyard; it’s a masterful application of chemistry, thermodynamics, and solid-state physics.

The Metal With an Invisible, Self-Healing Armor

Before 1913, any steel left out in the damp English air was destined for a single fate: a creeping orange-brown blight of rust. In a laboratory in Sheffield, a metallurgist named Harry Brearley was tasked with finding a more durable metal for gun barrels. He experimented with adding different elements to steel, and one of his chromium-steel alloys showed remarkable promise. After testing, he tossed the samples aside. Weeks later, he noticed that while the other metal scraps in his lab had rusted, his chromium-steel samples remained as bright and untarnished as the day they were forged. He hadn’t created a better gun barrel; he had accidentally discovered stainless steel.

What Brearley had stumbled upon was a chemical phenomenon called passivation. All steel is primarily iron, which has a natural, aggressive tendency to react with oxygen in the presence of water to form iron oxide—rust. This process is relentless, flaking away to expose fresh iron underneath, continuing until the metal is consumed.

The genius of stainless steel is the introduction of chromium. When at least 10.5% chromium is added to the alloy, something incredible happens at a microscopic level. The chromium on the surface also reacts with oxygen, but instead of forming a flaky, destructive rust, it creates an ultra-thin, transparent, and chemically inert layer of chromium oxide (Cr₂O₃). This is the passivation layer. It’s only a few nanometers thick, yet it’s incredibly dense and durable, forming a perfect barrier that seals the vulnerable iron within from the corrosive outside world.

Its most remarkable property, however, is that it’s self-healing. If you scratch the surface, the exposed chromium underneath instantly reacts with oxygen in the air and repairs the invisible armor. This is why a high-quality outdoor kitchen component, built from what’s known as 304-grade stainless steel, can withstand years of rain, heat, and acidic food spills. The “304” designation, often called “18/8,” signifies it contains approximately 18% chromium for a robust passive layer and 8% nickel, which enhances this corrosion resistance and gives the steel superior strength and formability. The simple, unblemished surface of an appliance like the Bull 21039 side burner isn’t just a design choice; it is a continuous, dynamic chemical event in action.

Quantifying Fire and the Flavor It Creates

We instinctively understand the difference between a weak, flickering flame and a roaring one, but how do we scientifically measure the power of fire? The answer lies in a unit of energy conceived during the Industrial Revolution: the BTU, or British Thermal Unit. One BTU is the amount of energy required to raise the temperature of one pound of water by one degree Fahrenheit. It’s a beautifully tangible way to quantify heat.

When a side burner is rated at 15,000 BTUs, it means it has the capacity to release a tremendous amount of thermal energy every hour. This energy is transferred to your cookware through three distinct physical processes. Conduction is the direct transfer of heat from the hot metal grate to the pan. Convection is the transfer of heat through the movement of hot air and combustion gases swirling around the pan. And Radiation is the direct transmission of infrared energy from the incandescent flames themselves.

A high BTU output dramatically increases the rate of all three. This isn’t just about boiling water faster; it’s about controlling chemical reactions. The most important of these in cooking is the Maillard reaction, the complex dance between amino acids and reducing sugars that occurs at high temperatures (typically above 280°F or 140°C). This reaction is responsible for creating hundreds of new aromatic compounds, giving seared steaks, toasted bread, and fried onions their deep, savory flavor and brown color.

A low-power flame transfers heat too slowly. The surface of the food steams and turns gray before it has a chance to brown properly. A 15,000 BTU burner, however, delivers a high enough energy flux to overcome the cooling effect of moisture evaporating from the food, allowing the surface to quickly reach the temperatures needed for a vigorous Maillard reaction. That perfect, flavorful crust on a batch of sautéed vegetables is a direct result of well-managed thermodynamics.

The Crystal That Breathes Lightning

Perhaps the most elegant piece of science in the modern grill is the ignition. You push a knob, you hear a click, and a spark appears from seemingly nowhere. There’s no battery to replace, no flint to wear down. This is thanks to a bizarre and wonderful phenomenon known as the piezoelectric effect.

Discovered in 1880 by French brothers Pierre and Jacques Curie (Pierre would later become famous for his work on radioactivity with his wife, Marie), piezoelectricity—from the Greek piezein, “to press or squeeze”—is the ability of certain crystals to generate a voltage when subjected to mechanical stress.

Inside that ignition button is a small, spring-loaded hammer aimed at a specially formulated ceramic or quartz crystal. These crystals have a highly ordered, asymmetrical internal lattice of positive and negative ions. In its resting state, the charges are perfectly balanced. But when you push the button, the hammer strikes the crystal with a sharp, sudden force. This mechanical impact deforms the crystal lattice, squishing it and knocking the charge centers out of alignment. One face of the crystal develops a net positive charge, and the opposite face develops a net negative charge.

This instantaneous separation of charge creates a massive electrical potential—often thousands of volts. This high voltage is strong enough to ionize the air in the small gap between two electrode points near the gas outlet, creating a visible spark that ignites the fuel. The simple click is the sound of a mechanical force being converted directly into electrical energy. It is a perfect, self-contained system—a miniature lightning storm generated on demand. This is why piezo igniters are so astonishingly reliable in outdoor settings; their genius lies in their utter simplicity and independence from fragile electronics or power sources.

From the self-healing armor of stainless steel to the quantified power of a flame and the lightning captured in a crystal, the objects we use to gather and eat are testaments to more than a century of scientific discovery. They are the physical embodiment of curiosity, accident, and genius, hiding in plain sight, waiting to be understood.