Corn syrup is a thick, sweet liquid sweetener created by breaking down corn starch into simple sugars, primarily glucose. This viscous product is widely used in commercial food production and home baking to control sugar crystallization and preserve moisture. In its standard liquid form, corn syrup is generally not considered a combustible or flammable material under normal conditions. This classification is primarily due to its unique composition, which acts as a barrier against ignition.
Why Corn Syrup Resists Fire
The main reason standard corn syrup resists fire is its substantial water content, which typically ranges from 19 to 30% by weight. For any material to combust, it must first reach its ignition temperature. The water mixed into the syrup acts as a heat sink, absorbing thermal energy.
Before the sugars can ignite, this water must be heated to its boiling point and completely evaporated away, a process that demands a sustained input of heat energy. This energy absorption prevents the syrup’s temperature from rising quickly enough to support combustion. Corn syrup is resistant to ignition from brief exposure to a flame or a spark, and safety data sheets often list it as nonflammable.
The Sugars as Potential Fuel
Despite its resistance to fire in its liquid state, the sweet components within corn syrup are organic compounds that have the potential to burn. Corn syrup is an aqueous solution of sugars like glucose, dextrose, and maltose, all of which are carbohydrates. Once the water is removed, these dehydrated sugars become a combustible fuel source.
Under extreme and prolonged heat, far above the boiling point of water, the sugars will begin a process called thermal decomposition or pyrolysis. During pyrolysis, the complex sugar molecules break down into flammable gases, carbon monoxide, and volatile liquids. This process typically begins when the temperature of the sugar reaches approximately 320–356°F (160–180°C).
If the heat is maintained, these flammable decomposition products can ignite, often resulting in a smoky, charring fire rather than a rapid flame. What remains after this intense heating is a charred, carbon-rich residue. This demonstrates that the sugar component of the syrup acts as fuel once the protective water barrier is overcome.
Kitchen Safety and High Heat
Understanding the nonflammable nature of liquid corn syrup is important, but it does not remove all risk when heating it in the kitchen. The primary hazard associated with corn syrup during cooking is not fire, but the danger of severe thermal burns from its superheated state. When corn syrup is heated, such as in candy-making, its temperature can easily rise far above the boiling point of water.
Superheated corn syrup, with its thick and viscous consistency, adheres to the skin and transfers heat efficiently, causing deep burns upon contact. If a spill occurs on a hot surface, the syrup’s water content can flash to steam, causing the remaining sugar to rapidly reach pyrolysis temperatures and potentially smoke or char. Handle heated syrup with caution to prevent accidental spills and store unused corn syrup in a cool, dry place.