Until the mid 1880s milk was dipped from large cans into the consumer’s own containers. January 11, 1878, is commonly cited as the date on which milk was first delivered in sterilized glass bottles in the United States. Alexander Campbell of the New York Dairy Company stated before the New York State Senate that his company began such deliveries in that year. The date is commemorated annually as National Milk Day.
A related development was the Lester milk jar, patented in the United States on January 29, 1878, by George Henry Lester. The patent described a reusable glass milk container with a wide mouth and neck, intended to facilitate cleaning. It featured a mechanical closure system, including a cover and gasket, designed to reduce air exposure during transport and storage.
Hervey D. Thatcher of Potsdam, New York, developed the Common-Sense milk bottle. The sealing system, consisting of a flat, disposable disk and a bottle opening designed to receive it, was patented on September 17, 1889, by Harvey Patten Barnhart and Samuel Lindsey Barnhart. The bottle was distributed commercially by the Thatcher Manufacturing Co. It featured an internal shoulder near the mouth that supported a flat, disposable disk made of wood. The disk formed a tight seal when pressed into place and could be removed at the time of use.
The glass milk bottle was the main container of retail distribution until World War II, when wax-coated paper containers were introduced. Plastic-coated paper followed and became the predominant container. Today more than 75 percent of retail sales are in translucent plastic jugs. Glass bottles make up less than 0.5 percent of the business and are used mostly at dairy stores and for home delivery.
Modern packaging machines are self-cleaning and provide an aseptic environment for milk packaging. Their improved design has allowed milk to remain fresh for at least 14 days and has made it possible for use with ultrapasteurizing equipment for extended shelf-life applications.
Specialty milks
Many specialty milks are now available (even in remote areas) as a result of the 45-day refrigerated shelf life of ultrapasteurized milk. One of the most useful products, lactose-reduced milk, is available in both nonfat and low-fat composition as well as in many flavored versions. The lactose (milk sugar) is reduced by 70 to 100 percent, making it possible for lactose-intolerant individuals to enjoy the benefits of milk in their diets. Lactose reduction is accomplished by subjecting the appropriate milk to the action of the enzyme lactase in a refrigerated tank for approximately 24 hours. The enzyme breaks down the lactose to more readily digestible glucose and galactose. The reaction is halted when the lactose is consumed or when the milk is heat-treated. The resulting beverage is sweeter than regular milk but acceptable for most uses.
Other specialty milks include calcium-fortified, special and seasonal flavors (e.g., eggnog), and high-volume flavored milk shakes (frequently served in schools).
Condensed and dried milk
Condensed and evaporated milk
Whole, low-fat, and skim milks, as well as whey and other dairy liquids, can be efficiently concentrated by the removal of water, using heat under vacuum. Since reducing atmospheric pressure lowers the temperature at which liquids boil, the water in milk is evaporated without imparting a cooked flavor. Water can also be removed by ultrafiltration and reverse osmosis, but this membrane technology is more expensive. Usually about 60 percent of the water is removed, which reduces storage space and shipping costs. Whole milk, when concentrated, usually contains 7.5 percent milk fat and 25.5 percent total milk solids. Skim milk can be condensed to approximately 20 to 40 percent solids, depending on the buyer’s needs.
Condensed milk is often sold in refrigerated tank-truck loads to manufacturers of candy, bakery goods, ice cream, cheese, and other foods. When preserved by heat in individual cans, it is usually called “evaporated milk.” In this process the concentrated milk is homogenized, fortified with vitamin D (A and D in evaporated skim milk), and sealed in a can sized for the consumer. A stabilizer, such as disodium phosphate or carrageenan, is also added to keep the product from separating during processing and storage. The sealed can is then sterilized at 118 °C (244 °F) for 15 minutes, cooled, and labeled. Evaporated milk keeps indefinitely, although staling and browning may occur after a year.
New ultrahigh-temperature (UHT) processing and aseptic filling of foil-lined cardboard or metal cans is also practiced. Although this process is more costly, the scorched flavor is not as pronounced as with conventionally processed evaporated milk.
Sweetened condensed milk is also made by partially removing the water (as in evaporated milk) and adding sugar. The final product contains about 8.5 percent milk fat and at least 28 percent total milk solids. Sugar is added in sufficient amount to prevent bacterial action and subsequent spoilage. Usually, at least 60 percent sugar in the water phase is required to provide sufficient osmotic pressure for prevention of bacterial growth. Because sweetened condensed milk (or skim milk) is preserved by sugar, the milk merely needs to be pasteurized before being placed in a sanitary container (usually a metal can).