Black spots on dried lemon slices are signs of impending decay. The whole lemon can be stored at room temperature for about one month. When the concentration of oxygen is lower than 3% and the concentration of carbon dioxide is higher than 10% for a period of time, its flavor will be adversely affected. Carbon dioxide exceeding 10% will increase the decay of lemon and reduce the acidity. Less than 5% oxygen will produce lemon flavor. You can wrap the lemon in plastic wrap and keep it in the refrigerator.

It may be the natural pigmentation of lemon, or it may be caused by mold infection. The black spots on the lemon peel may be a sign of impending decay, so eat them as soon as possible. It is important to distinguish the nature of the black spots on the lemon peel. If this black spot is naturally pigmented, there is no problem. If it is infected by mold, it cannot be eaten. When choosing lemons, you must choose lemons with yellow surfaces and uniform color distribution.