Have you ever opened a bar of chocolate and found grayish streaks across the surface? Or noticed something that looked like dust? These are actually two forms of chocolate bloom, one from fat and the other from sugar.
Fat bloom happens if the chocolate gets too warm. The cocoa butter melts and then re-solidifies, leaving those gray streaks.
Sugar bloom happens if the chocolate was stored in a damp area. Moisture collects on the surface of the chocolate and draws out the sugar. When the moisture evaporates, it leaves behind a grit of sugar crystals across the surface.
Both these types of blooms happen when chocolate is stored improperly. Chocolate should ideally be stored in an air-tight container at about 70-degrees or so.
This can be a tall order during hot and muggy summer months ahead! Resist the temptation to put chocolate in the fridge, which is too humid for chocolate. Instead, invest in a good air-tight container and store the chocolate in a cool part of your kitchen--like a low shelf or closet.
If you still find bloom on your chocolate, no worries! Bloom is perfectly consumable and doesn't affect flavor. If you're melting the chocolate down or chopping it up for cookies, the bloom will re-integrate into the chocolate with none the wiser.