Reader Jey asks if I would talk a little about chocolate bloom and provide some tips for preventing it. Jey, I would be delighted. First let’s define our terms. The grey streaks or spots that appear on chocolate when it melts and re-firms, or when it’s stored for long periods in the refrigerator or freezer, is called “chocolate bloom”. There are two kinds of it: fat bloom and sugar bloom. Both have different causes and fixes.
Fat bloom is caused by cocoa butter pooling up and forming crystals. This doesn’t happen when chocolate is tempered properly because a.) the controlled cooling process keeps the chocolate emulsion nice and stable and b.) it creates a strong and even crystal structure. However untempered chocolate, being something of a riot of different sorts of fat crystals, is prone to unsightly streaks.
Sugar bloom is a different phenomenon, familiar to anyone who’s refrigerated or frozen chocolate for any period of time. Sugar bloom happens when moisture droplets contact the surface of solid chocolate. When that happens the sugar on the surface of the chocolate dissolves into the water and becomes syrup. In time the water evaporates leaving a spot of crystallized sugar behind.
The problem is exacerbated when chocolate is repeatedly chilled and warmed. So for instance if you have a large chocolate bar in the refrigerator or freezer and you occasionally take it out to chip a bit off, you get condensation on the chocolate bar when it meets the warm air. When you put the chocolate back in the chill chest the syrup-evaporation thing happens, and the cycle is repeated with every removal. Pretty soon a large proportion of the sugar is drawn out, and because long-term freezing also exacerbates fat bloom, shortly your expensive chocolate bar has the mouthfeel of sidewalk chalk. The same thing happens if you have a habit of leaving the refrigerator or freezer door open for a long period of time.
The good news is that while both types of bloom compromise both the appearance and the texture of chocolate you can undo the damage by simply-remelting the chocolate. It goes right back to normal.