Because of their generally low water content and concentrated sugars, which draw moisture out of living cells, candies are seldom spoiled by the growth of bacteria or molds. Their flavor can be degraded, however, by the oxidation and consequent rancidity of added fats, whether in milk solids or butter. This process can be slowed down by refrigeration or freezing, but cold storage encourages another problem called “sugar bloom.” Changes in temperature can cause moisture from the air to condense on the candy surface, and some sugar will dissolve into the liquid. When the moisture evaporates again or is drawn deeper into the candy, the surface sugar crystallizes into a rough, white coating. Airtight wrapping will prevent sugar bloom.