A kipper is a whole herring, a small, oily fish, that has been split in a butterfly fashion from tail to head along the dorsal ridge, gutted, salted or pickled, and cold-smoked over smouldering wood. Kippers are a traditional British breakfast food, enjoyed for high tea and supper, that were popular in the Victorian and Edwardian eras. They are high in Omega 3 and are quick and easy to cook, whether frozen, "in the bag" or chilled. Kippers are a sustainable fish and are on the Marine Conservation Societys list of fish to eat. Kippering is a process where a fish is split down the middle, cleaned out, salted, and then smoked. The term "kipper" is thought to derive from the Old English cypera, or copper, based on the color of the fish. As a verb, kippering ("to kipper") means to preserve by rubbing with salt or other spices before drying in the open air or in smoke. Kippers are best eaten within a week if fresh and chilled, but will keep longer if frozen or vacuum-packed.