If you are in the habit of maintaining an emergency stockpile of chocolate for stressful days, you may occasionally find that some of your supply has become outdated. This raises the obvious question of whether you can still eat the chocolate, especially if it's all you have left and you really, really need some.
Pure chocolate is not a single substance, but a mixture of them. Its chemistry is complex and not entirely understood, but in simple terms chocolate is made up of two things. The first is its flavor ingredients, the cocoa solids. These make chocolate taste the way it does, and contain the active ingredients that make it so pleasurable for our brains. The second is cocoa butter, a collection of fats that give the chocolate its rich mouth feel and physical form. Chocolate sold for eating adds at least a small amount of sweetening, and may include many other ingredients as well.
Fortunately for absent-minded chocolate lovers, it's not a very perishable food. Pure chocolate contains little moisture, a necessity for bacterial life. This, and its high fat content, give chocolate a lengthy shelf life if it's kept in a cool, dry place. Of course, this only considers edibility. Although it seldom becomes dangerous to eat, chocolate's flavor and texture will eventually deteriorate. Also, the possibility of your chocolate absorbing off flavors from its surroundings increases with the passage of time.
Deterioration of Pure Chocolate
The most visible symptom of aging chocolate is the appearance of a dull off-white, powdery-looking substance on its surface. Often it's mistaken for mold, and the chocolate is discarded. If fact, the powder is nothing more than crystals of cocoa butter rising to the surface. The chocolate remains edible, though the texture becomes crumbly. In the case of pure chocolate, it can easily be melted and reused. Over long periods, especially in warm climates, the cocoa butter itself can eventually oxidize and become rancid. There is no remedy for that, and the chocolate should be discarded.
Candy bars and other confections made from chocolate don't necessarily age in the same way that pure chocolate does. Manufacturers often replace cocoa butter with cheaper fats, which may oxidize more quickly. Ingredients including nuts, dried fruit, dairy products and peanut butter are all prone to spoilage, rancidity and off flavors. In some cases, the chocolate is adulterated enough to allow the growth of mold. Any visible mold means the chocolate should be discarded. Aside from that, the issue is more one of flavor than edibility.