Chocolate Bloom is the white areas that appear on chocolate.
In addition to affecting appearance and making the chocolate look old, Chocolate Bloom can change the texture and flavour, though minimally.
There are two types of bloom, sugar and fat.
Sugar bloom feels grainy. It happens when chocolate is stored in too-damp conditions and the moisture dissolves some of the sugar that it comes in contact with. When the moisture evaporates, the sugar re-crystallizes as a fine powder on the surface. It can also be caused by condensation occurring when cold chocolate is brought into a warm area.
Fat bloom feels oily. It happens when chocolate is stored in too-hot conditions. It is a greyish-white patch that looks a bit like mould or powder. It is a result of the Cocoa butter separating from the rest of the chocolate, and rising to the surface and what you are actually seeing is large cocoa butter crystals. It is often accompanied by very fine cracks that cause the surface of the chocolate to look dull. Humid and warm temperatures can bring it on. It can occur as well when the chocolate wasn't tempered or cooled properly.
Either Chocolate Bloom can be dealt with by melting the chocolate, but if it's sugar bloom, the chocolate isn't good for fine candies afterwards.
The chocolate industry is still investing money to figure out the exact causes of this. Though they know the conditions that can bring it on, they don't really understand how Chocolate Bloom exactly forms. It can occur even in well-tempered chocolate. (See Temper for more information.)
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