Colby, a type of cheddar cheese, originates in the United States and is a traditional semi-soft cheese made from cow's milk. The sizes vary, but they are generally block-shaped and free of rind. It is a washed-curd cheese, which means that the curds are thoroughly rinsed in fresh water to remove all excess whey and any stray lactose. This prevents the acidity in the curd from rising, so the cheese remains soft and springy, with a sweet and mild flavor. Colby has a higher moisture content than regular cheddar and feels more elastic. It is also sweetly flavored, rather than savory. This cheese ripens in four months. Colby must be consumed shortly after purchase or it dries out and loses its flavor.