1. Before opening the bottle, if you find that the cork is protruding from the bottle, it means the wine may have been exposed to high temperatures, causing the pressure inside the bottle to rise and the cork to pop out.
2. If a red wine has a dull color, lacks luster, or appears brownish, it may have been over-oxidized or contaminated by other factors. Similarly, if a white wine has a very deep yellow color, it may also have undergone excessive oxidation.
3. If you find bubbles in a non-sparkling wine, it means the wine has likely undergone a secondary fermentation in the bottle. However, not all secondary fermentations are signs of spoilage; some wines are specially handled by the winemaker to continue fermenting after bottling, such as Vinho Verde from Portugal.