Wine acts as a solvent due to its composition, primarily being a solution of water and ethanol, which are completely miscible and can mix in any proportion. In contrast, sugar is a solid and functions as a solute when dissolved in water, which serves as the solvent. The concept of solubility is key, as it defines how much solute can dissolve in a solvent. A solution is characterized by the presence of both a solvent and a solute, which can be gases, liquids, or solids of different chemical compositions.