Bourbon is a type of American whiskey defined by specific production requirements. To be legally classified as bourbon, the spirit must be made from a mash bill containing at least 51% corn, aged in new, charred oak barrels, and bottled at a minimum of 80 proof (40% alcohol by volume, or ABV). The combination of alcohol and water means that bourbon’s freezing point is dramatically lower than that of plain water. Therefore, the temperature at which bourbon freezes is directly tied to its alcohol concentration.
The Chemistry of Freezing Point Depression
The reason bourbon resists freezing is rooted in freezing point depression. This chemical phenomenon describes how adding a solute, such as ethanol, to a solvent like water, lowers the mixture’s freezing temperature. Water molecules naturally form ice at \(32^{\circ}\text{F}\) (\(0^{\circ}\text{C}\)) by arranging into a rigid, crystalline structure. Ethanol molecules interfere with this alignment, physically blocking the water from forming its solid lattice structure. Since pure ethanol freezes at approximately \(-173^{\circ}\text{F}\) (\(-114^{\circ}\text{C}\)), bourbon’s freezing point is dramatically lower than water. The higher the proportion of ethanol, the lower the temperature required for the liquid to solidify.
How Proof Determines the Freezing Temperature
The freezing temperature of bourbon is directly linked to its proof, which measures its alcohol content. Since nearly all bourbons are bottled at 80 proof (40% ABV) or higher, they all exhibit a significantly depressed freezing point. A standard 80-proof bourbon has a freezing point of approximately \(-17^{\circ}\text{F}\) (\(-27^{\circ}\text{C}\)), a temperature far below the coldest setting of most residential freezers. The freezing point drops rapidly as the alcohol concentration increases, making higher-proof bourbons more resistant to solidification.
A Bottled-in-Bond bourbon (100 proof/50% ABV) requires a temperature closer to \(-35^{\circ}\text{F}\) (\(-37^{\circ}\text{C}\)) to freeze solid. Barrel-proof or cask-strength bourbons, which can reach 120 proof (60% ABV) or higher, have freezing points that can fall below \(-50^{\circ}\text{F}\) (\(-45^{\circ}\text{C}\)). For every five-point increase in proof above 80, the freezing point drops by several degrees Fahrenheit. This relationship confirms that freezing bourbon solid in a home setting is nearly impossible for anything bottled at 80 proof or higher.
Optimal Storage and Chilling Practices
A standard residential freezer is typically set to maintain a temperature around \(0^{\circ}\text{F}\) (\(-18^{\circ}\text{C}\)). Since 80-proof bourbon freezes at \(-17^{\circ}\text{F}\) (\(-27^{\circ}\text{C}\)), storing it in a home freezer will not cause it to freeze solid. However, chilling bourbon is generally not recommended for enjoying the spirit’s full complexity. Extreme cold suppresses the volatile organic compounds responsible for bourbon’s aroma and flavor profile.
When bourbon is chilled to near-freezing temperatures, the flavor experience becomes muted and subdued. Putting bourbon in a freezer can also increase its viscosity, giving it a thicker mouthfeel. Excessive chilling can cause a temporary “chill haze” or cloudiness in bourbons that have not been chill-filtered. Storing bourbon at room temperature or slightly below, between \(60^{\circ}\text{F}\) and \(70^{\circ}\text{F}\) (\(15^{\circ}\text{C}\) and \(21^{\circ}\text{C}\)), allows the full range of flavors to be appreciated.