If you opened a bar of chocolate and discovered greying surface, that could be either sugar bloom or fat bloom.
Sugar bloom occurs when the chocolate has been exposed to too much moisture in the storage. The surface moisture dissolves the sugar in the chocolate. Once the moisture evaporates, sugar crystals remain on the surface. If this process is repeated, the surface can become sticky and even more discolored. Sugar bloom is most often the result of overly humid storage. Sugar bloom can also happen when the chocolate has been stored at a relatively cool temperature and then moved too quickly into a much warmer surrounding. Sugar bloom is one of the reasons why chocolates should not be stored in the refrigerator.
Fat bloom is similar to sugar bloom, except that it is fat or cocoa butter that is separating from the chocolate and deposited on the surface. Similarly to sugar bloom, the most common causes of fat bloom are quick temperature changes and overly-warm storage.
Although the two type of blooms cause the chocolates to look less than perfect but it should still taste good.
The following is a guideline for storing chocolates:
Temperature: Keep your chocolates in a cool and dark place between 18°C and 20°C and without too much humidity. It is very tempting to store chocolates in the fridge but once the chocolate is out from the fridge condensation occurs. This will cause sugar bloom and dries out the chocolates.
Odor absorption: Chocolate consists of sugar and fat which have the ability to absorb smells from things around them. If the “cool and dark place” happens to be a cabinet that holds a fine, melting piece of camembert, you might want to find another “home” for your chocolates.
Shelf-life: Pralines filled with fresh cream should be consumed in 2 weeks up to a month. On the other hand chocolates without fillings can have shelf-life as long as a year or more if stored properly.