In order to determine egg quality without actually breaking them, producers candle their eggs, or place them in front of a light bright enough to pass through them and illuminate their contents. (Candle and eye were the original equipment; today electric lights and scanners do the work automatically.) Candling readily detects cracks in the shell, harmless but unappealing blood spots on the yolk (from burst capillaries in the hen’s ovary or yolk sac), and “meat spots” in the whites (either brown blood spots or tiny bits of tissue sloughed off from the oviduct wall), and large air cells, all characteristics that relegate an egg to the lower grades. To determine the condition of the yolk and white, the egg is quickly twirled. The yolk’s shadow will remain indistinct if its membrane is strong enough and the white thick enough to have kept it from getting close to the shell. If the yolk is easy to see, then it’s too easily deformed or mobile, and the egg is of lower quality