Milk can be preserved for a while by a process called pasteurization. Milk is pasteurized by heating it at 60C for thirty minutes. The microorganisms in the milk are killed, and it becomes pure enough to be drunk without boiling.
Pasteurization or pasteurisation is a process in which certain packaged and non-packaged foods (such as milk and fruit juice) are treated with mild heat, usually less than 100 °C (212 °F), to eliminate pathogens and extend shelf life. The process is intended to sterilize foods by destroying or inactivating organisms that contribute to spoilage, including vegetative bacteria but not bacterial spores.[1][2]
The process was named after the French scientist Louis Pasteur, whose research in the 1880s demonstrated that thermal processing would inactivate unwanted microorganisms in wine.[2][3] Spoilage enzymes are also inactivated during pasteurization. Today, pasteurization is used widely in the dairy industry and other food processing industries to achieve food preservation and food safety.[3]
Most liquid products are heat treated in a continuous system where heat can be applied using a plate heat exchanger and/or the direct or indirect use of hot water and steam. Due to the mild heat, there are minor changes to the nutritional quality and sensory characteristics of the treated foods.[4] Pascalization or high pressure processing (HPP) and pulsed electric field (PEF) are non-thermal processes that are also used to pasteurize foods
History
The process of heating wine for preservation purposes has been known in China since AD 1117,[5] and was documented in Japan in the diary Tamonin-nikki, written by a series of monks between 1478 and 1618.
Much later, in 1768, Italian priest and scientist Lazzaro Spallanzani's research proved a product could be made "sterile" after thermal processing. Spallanzani boiled meat broth for one hour, sealed the container immediately after boiling, and noticed that the broth did not spoil and was free from microorganisms.[2][6] In 1795, a Parisian chef and confectioner named Nicolas Appert began experimenting with ways to preserve foodstuffs, succeeding with soups, vegetables, juices, dairy products, jellies, jams, and syrups. He placed the food in glass jars, sealed them with cork and sealing wax and placed them in boiling water.[7] In that same year, the French military offered a cash prize of 12,000 francs for a new method to preserve food. After some 14 or 15 years of experimenting, Appert submitted his invention and won the prize in January 1810.[8] Later that year, Appert published L'Art de conserver les substances animales et végétales (or The Art of Preserving Animal and Vegetable Substances). This was the first cookbook of its kind on modern food preservation methods.[9][10]
La Maison Appert (English: The House of Appert), in the town of Massy, near Paris, became the first food-bottling factory in the world,[7] preserving a variety of foods in sealed bottles. Appert's method was to fill thick, large-mouthed glass bottles with produce of every description, ranging from beef and fowl to eggs, milk and prepared dishes. He left air space at the top of the bottle, and the cork would then be sealed firmly in the jar by using a vise. The bottle was then wrapped in canvas to protect it while it was dunked into boiling water and then boiled for as much time as Appert deemed appropriate for cooking the contents thoroughly. Appert patented his method, sometimes called appertisation in his honor