to a spreadable consistency around 15 °C (60 °F), well above refrigerator temperatures. The "butter compartment" found in many refrigerators may be one of the warmer sections inside, but it still leaves butter quite hard. Until recently, many refrigerators sold in New Zealand featured a "butter conditioner", a compartment kept warmer than the rest of the refrigerator—but still cooler than room temperature—with a small heater. Keeping butter tightly wrapped delays rancidity, which is hastened by exposure to light or air, and also helps prevent it from picking up other odors. Wrapped butter has a shelf life of several months at refrigerator temperatures. Butter can also be frozen to extend its storage life. Packaging United States In the United States, butter has traditionally been made into small, rectangular blocks by means of a pair of wooden butter paddles. It is usually produced in sticks that are individually wrapped in waxed or foiled paper, and sold as a package of 4 sticks. This practice is believed to have originated in 1907, when Swift and Company began packaging butter in this manner for mass distribution. Due to historical differences in butter printers (machines that cut and package butter), 4-ounce sticks are commonly produced in two different shapes: The dominant shape east of the Rocky Mountains is the Elgin, or Eastern-pack shape, named for a dairy in Elgin, Illinois. The sticks measure and are typically sold stacked two by two in elongated cube-shaped boxes. West of the Rocky Mountains, butter printers standardized on a different shape that is now referred to as the Western-pack shape. These butter sticks measure and are usually sold with four sticks packed side-by-side in a flat, rectangular box. Most butter dishes are designed for Elgin-style butter sticks. Elsewhere Outside of the United States, butter is measured for sale by mass (rather than by volume or unit/stick), and is often sold in and packages. Bulk packaging Since the 1940s, but more commonly the 1960s, butter pats have been individually wrapped and packed in cardboard boxes. Prior to use of cardboard, butter was bulk packed in wood. The earliest discoveries used firkins. From about 1882 wooden boxes were used, as the introduction of refrigeration on ships brought about longer transit times. Butter boxes were generally made with woods whose resin would not taint the butter, such as sycamore, kahikatea, hoop pine, maple, or spruce. They commonly weighed a firkin - .