How should I store this oil after opening, and how do I know if it has gone bad?

Store the bottle in a cool, dark place — a kitchen cabinet away from the stove, window, or other heat sources is ideal. Keep the cap tightly closed. Light and air accelerate oxidation of the fatty acids, which is what makes the oil go rancid. The 500 ml bottle is a practical size for a family to use within a few weeks of opening.

If you keep it in the refrigerator, the oil may become slightly cloudy or even solidify — this is normal and does not affect quality. It will return to a clear liquid at room temperature.

To check freshness, smell the oil. Fresh cold-pressed sunflower oil has a pleasant, nutty, sunflower-seed aroma. If it smells sharp, like old nuts, paint, or something sour, it has oxidized and should be discarded. The taste will also become bitter. If you notice any off-smell, do not use it.