The short answer is that while the orange peel itself does not easily ignite, the oils contained within it are highly flammable. The peel’s structure acts like a protective barrier, preventing the rapid combustion of its flammable components under normal conditions. The distinct orange scent comes from these oils, which are volatile hydrocarbons that can be coaxed into a brief, bright flame if released correctly.
The Volatile Component: Limonene
The primary flammable agent in an orange peel is D-limonene, a colorless liquid that makes up over 90% of the essential oil found in citrus rinds and provides the characteristic citrus aroma. The oil is stored in numerous minute structures known as secretory cavities or oil glands, which are embedded within the outermost, pigmented layer of the peel called the flavedo.
Limonene is flammable because its flash point—the lowest temperature at which its vapors ignite—is relatively low at approximately 50 °C (122 °F). When exposed to heat or pressure, the oil quickly transitions into a gaseous state. Once released, this volatile oil readily mixes with oxygen, creating a combustible mixture that ignites easily.
Why Whole Peels Resist Burning
Despite containing a highly flammable oil, a whole orange peel will not easily catch fire because of its high moisture content and dense, layered structure. Fresh orange peels are composed primarily of water, which acts as a powerful fire retardant. Before combustion can occur, the heat from an external flame must first expend energy to raise the temperature of this water and convert it to steam.
The energy required to evaporate this large volume of water prevents a sustained burn. The peel’s fibrous interior, the albedo, also provides a dense matrix that insulates the flammable oils in the flavedo. This structural layer physically restricts the access of oxygen to the bulk of the oil content, meaning the peel typically only chars on the surface.
Controlled Ignition and Safety
The flammability of orange oil is demonstrated through the practical method known as the “flame twist” or “spritz,” often used in mixology. This technique sidesteps the peel’s defenses by mechanically releasing the oil. Squeezing a small piece of peel forcefully causes the cell walls of the oil glands in the flavedo to rupture instantaneously.
This action ejects the oil under pressure as a fine mist, a process called aerosolization. The tiny oil droplets instantly vaporize and mix thoroughly with the surrounding air, creating an ideal fuel-air mixture. When this mist passes through an open flame, the low flash point of the limonene allows for immediate ignition, producing a momentary flash of fire. Anyone attempting this demonstration should proceed with caution, as open flames and flammable liquids pose a risk of burns or irritation.