Soda does freeze, but the process differs from freezing pure water. As a complex aqueous solution, soda contains water, dissolved solutes (like sugars or artificial sweeteners), and carbon dioxide gas. These components alter the liquid’s physical properties, requiring a colder temperature to solidify completely.
The Science Behind the Freezing Point
The presence of dissolved substances causes freezing point depression. This is a colligative property, meaning the reduction in freezing temperature relates directly to the number of solute particles present. Sugars, flavorings, and salts interfere with water molecules aligning into the highly ordered, crystalline structure necessary for ice formation.
To overcome this interference, the solution’s temperature must be lowered below the normal freezing point of pure water (\(32^{\circ}\text{F}\) or \(\text{0}^{\circ}\text{C}\)). The dissolved carbon dioxide gas also acts as a solute, contributing slightly to this depression. Highly concentrated sodas, especially those with high sugar content, can remain liquid well below the temperature at which plain water freezes solid.
The pressure inside a sealed container also plays a role in the phase change. The carbon dioxide is kept dissolved in the liquid under high pressure, which helps maintain the depressed freezing point. If the pressure is released, the freezing point of the liquid will actually increase because a solute (\(\text{CO}_2\)) has been removed from the solution.
Container Damage and Expansion
The most immediate consequence of freezing soda in its original container is the risk of rupture. Water is unique because ice is less dense than liquid water, causing it to expand in volume by approximately nine percent upon freezing. This volumetric increase causes pressure buildup.
In a sealed, rigid container like an aluminum can or glass bottle, this expansion has nowhere to go. The force generated by the expanding ice is strong enough to deform the container, often leading to bursting or breaking seams. As the water freezes, it also forces dissolved carbon dioxide out of solution, adding extra gas pressure to the stressed container.
The combination of the expanding ice and the escaping pressurized gas can cause a significant mess and potential hazard, especially with glass, which can shatter into sharp fragments. While a plastic bottle offers slightly more flexibility and may only bulge and deform, the internal pressure can still be intense, and the seal may fail.
Changes to Flavor and Texture After Thawing
Freezing permanently alters the soda’s sensory experience, primarily through the loss of carbonation. When the liquid freezes, the ice crystal structure cannot accommodate dissolved \(\text{CO}_2\) molecules, forcing the gas out of solution. Upon thawing, the soda is left “flat” because the carbonation, which contributes significantly to flavor and texture, has escaped.
In addition to becoming flat, the ingredients often separate during the freezing and thawing process. Since water freezes first, it leaves behind a concentrated, syrupy mixture of sugars and flavorings. When the ice melts, the result is an unevenly mixed liquid that may taste watery in some parts and overly sweet in others.
To minimize unpleasant effects, frozen and thawed soda should be carefully handled to avoid immediate rupture and then thawed slowly, ideally in a refrigerator. Even with careful thawing, the soda will have a noticeably different, less palatable texture and flavor due to the irreversible loss of fizz.