What issue may arise from not storing a cork-sealed wine on its side?

Storing cork-sealed wine on its side is important primarily because it helps keep the cork in contact with the wine. When the cork remains moist, it swells and maintains a solid seal between the wine and the outside environment. If the cork dries out—often due to prolonged exposure to air and lack of moisture—it can shrink or crack. This allows air to seep into the bottle, which can lead to oxidation of the wine, spoilage, and an overall decline in quality.

The other choices do not capture this essential aspect of preserving wine. For example, while fading of the label can occur due to light exposure, it’s not directly related to how the wine is stored. The temperature may indeed vary based on storage conditions, but wine becoming too cold is not a direct consequence of storing it upright or on its side. Additionally, while oxidation can happen if the cork dries out, it does not occur immediately as suggested in one option; it results from prolonged exposure following cork deterioration. Thus, the key reason for storing wine on its side centers around protecting the integrity of the cork to ensure the wine remains well-preserved.