We’ve all done it; you left your chocolate in the car overnight, and when you opened it up, it appeared dusted with a fine white film! Is it still safe to eat? Don’t worry; there’s not much you can do to your chocolate that would make it unsafe. The white sheen you see on your dashboard chocolate is a phenomenon known as “bloom”. Bloom can happen for several reasons, and it will usually change how the chocolate tastes and feels in your mouth. But it certainly won’t hurt you!

Most bloom is the result of changes in the fat portion of chocolate, known as cocoa butter. When chocolate is properly made, it goes through a process known as “tempering”, performed by heating and cooling the chocolate to very specific temperatures for the purpose of crystallizing its fats. Most people associate the word “crystal” with a hard, brittle substance, like glass or emeralds, but in fact, a crystal is any solid whose molecules are arranged in a repeating, orderly fashion. The fat molecules of cocoa butter can acquire six different conformations. Only one of these shapes, Type 5, fits together well in an orderly, repeating manner (in other words—it crystalizes well). All of the other conformations tend to fall into a jumbled mess. So, when chocolate is tempered, this is really a shorthand way of saying that all its fats have been arranged into repeating patterns of Type 5 crystals.

However, if the chocolate is exposed to changes in temperature, that orderly arrangement of Type 5 fat crystals will expand, contract, melt, or fall apart in places, causing some of the molecules to deteriorate into Type 1-4 crystals, which ooze onto the surface of the chocolate in a disorderly fashion, resulting in the “blobs” that you perceive as bloom. They appear white or sandy because the lower crystal types refract more light than the Type 5 forms. This means that while the remaining Type 5 crystals still appear shiny, the Type 1-4 crystals corrupting their surface will appear whitish or pearly. This, in a nutshell, is bloom.

Bloom may also be the result of moisture contact with the chocolate surface. This type of bloom is known as “sugar bloom” and it is characterized by a grainer appearance with less discoloration. While it may look similar, this type of bloom is unrelated to fat migration. Instead, it is caused when sugar from the chocolate dissolves into water that makes contact with its surface. When this water evaporates, the sugar is left behind and recrystallizes, visibly scarring the surface of the chocolate.

Bloom can be beautiful, but it is rarely delicious. Make every effort to store your chocolate in a low-moisture environment at cool room temperature. Better yet, why store it at all? Grab some friends, take some tasting notes, and don’t give that chocolate a chance to bloom.