Opening a chocolate bar and finding a white or greyish coating on its surface can make it look as though the chocolate has gone bad. In many cases, however, the discolouration is not mould. It is a phenomenon known as chocolate bloom.
There are two main types: fat bloom and sugar bloom. Both can affect the appearance, texture and flavour of chocolate, but when the coating really is chocolate bloom, it does not automatically make the chocolate unsafe to eat.
Why does chocolate develop a white coating?
The Canadian Food Inspection Agency explains in its guidance on chocolate bloom that two different processes can cause this familiar pale coating.
The first involves fat. Cocoa butter has a particular crystalline structure that can change when chocolate is exposed to conditions such as excessive heat or temperature fluctuations. Fat can migrate towards the surface and recrystallise there.
This is known as fat bloom. Instead of looking smooth and glossy, the chocolate may become dull, streaky, grey or whitish.
Research into fat bloom shows that its development can be influenced by temperature, tempering and the crystalline structure of the fats. In filled chocolates, oils and fats from the filling can also migrate into the chocolate coating and contribute to bloom.
What is the difference between fat bloom and sugar bloom?
Sugar bloom is caused by moisture rather than fat.
When moisture or condensation reaches the surface of chocolate, it can dissolve some of the sugar. As the water subsequently evaporates, the sugar crystallises again, leaving a pale coating that may look or feel rougher and grainier.
Scientific research on chocolate distinguishes sugar bloom from fat bloom, although both phenomena can sometimes occur together.
Sudden changes in temperature can therefore cause problems. Moving very cold chocolate directly into a warm, humid environment can allow condensation to develop on the surface, creating conditions that favour sugar bloom.
Is chocolate with white bloom safe to eat?
If the coating really is chocolate bloom, yes.
The Canadian Food Inspection Agency states that chocolate bloom is harmless and says bloomed chocolate can still be eaten or used for baking.
What may have deteriorated is its quality. The chocolate can look less appealing and its texture or flavour may no longer be at their best.
There is an important qualification, however: a white coating alone is not proof that every chocolate product is safe to eat.
A plain chocolate bar is different from a filled chocolate containing cream, ganache or other perishable ingredients. Visible mould, an unusual smell, damaged packaging or other signs of spoilage should not automatically be dismissed as harmless chocolate bloom.
How can you prevent chocolate bloom?
The main aim is to protect chocolate from heat, moisture and large temperature fluctuations.
The Canadian Food Inspection Agency recommends keeping chocolate in a consistently cool, dry place.
That also means the refrigerator is not automatically the ideal place to store chocolate. If refrigeration becomes necessary because the room temperature is too high, protecting the chocolate from moisture and condensation is particularly important, as is avoiding sudden changes between cold and warm environments.
If a plain chocolate bar has already developed bloom but shows no other signs of deterioration, it does not necessarily need to go to waste. Even when its appearance or texture is no longer perfect, it can still be useful for cakes, cookies, brownies or other recipes in which the chocolate will be melted.
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