Pasteurization

Unlike sterilization, which uses aggressive heat to kill all life forms (including spores), pasteurization is a "mild" treatment, typically staying below 100 °C (212 °F). Its goal is twofold: eliminate pathogens like Salmonella and Listeria while deactivating enzymes that cause spoilage. Because the heat is relatively low, the nutritional quality and sensory characteristics—the taste and "mouthfeel" of milk or juice—remain largely intact.

While heat is the traditional tool, modern industry is expanding the definition. Non-thermal processes like Pascalization (high-pressure processing) and Pulsed Electric Fields (PEF) achieve the same preservation goals without using heat at all. These methods are increasingly popular for premium products where even minor heat-induced flavor changes are undesirable.

The practice of heating beverages for preservation dates back to 12th-century China, but the modern science was forged in 19th-century France. In 1795, chef Nicolas Appert won a 12,000-franc military prize for inventing "appertisation"—sealing food in glass jars and boiling them. This laid the groundwork for the canning industry, though Appert didn't fully understand why his method worked; he just knew it did.

Louis Pasteur provided the "why" in the 1860s. Tasked with helping the local wine industry combat acidity, he discovered that heating young wine to just 50–60 °C (122–140 °F) killed the microbes responsible for souring without damaging the vintage. Ironically, while the process bears Pasteur's name, it was originally intended for alcohol; it would be decades before the technique was widely applied to milk.

In the 19th century, milk was a primary vector for lethal diseases, including tuberculosis and scarlet fever. As cities grew and supply chains lengthened, "raw" milk often arrived days old and teeming with bacteria. In England and Wales alone, 65,000 people died from milk-borne tuberculosis between 1912 and 1937. The danger was so high that raw milk was once considered one of the world’s most hazardous consumer products.

The shift to mandatory pasteurization was a hard-won battle of the early 20th century. Pioneers like Ernst Lederle and Milton Joseph Rosenau established the first rigorous standards (60 °C for 20 minutes). New York City mandated the process in 1910, and federal U.S. requirements followed in 1973. Today, the impact is undeniable: between 1998 and 2011, nearly 80% of dairy-related disease outbreaks in the U.S. were linked to the small fraction of the population still consuming raw milk products.

Modern pasteurization is a continuous, high-speed flow process rather than a static "cook." Most liquids pass through heat exchangers—sophisticated systems of plates or tubes that transfer heat between fluids without mixing them. This allows for High-Temperature Short-Time (HTST) treatment, where milk is flashed to 71.5 °C for a mere 15 seconds, killing pathogens while maintaining high throughput.

For products requiring a longer shelf life, Ultra-High Temperature (UHT) processing pushes the temperature to 135 °C (275 °F) for just 1–2 seconds. When combined with sterile, aseptic packaging, UHT milk can sit on a shelf without refrigeration for up to nine months. If a system failure occurs and the temperature drops even slightly during processing, automated flow diversion valves instantly redirect the under-processed liquid back to the start.

Confirming that pasteurization worked by looking for bacteria is slow and expensive; by the time the lab results come back, the milk's shelf life would be half over. Instead, the industry uses enzymes as internal sensors. In milk, the enzyme alkaline phosphatase is the primary indicator. Because this enzyme is slightly more heat-resistant than the toughest common milk pathogens, its destruction serves as a "proxy" guarantee that the pathogens are also dead.

Similarly, the effectiveness of pasteurizing liquid eggs is verified by measuring the residual activity of the enzyme α-amylase. This biochemical shorthand allows for real-time safety verification, ensuring that every carton leaving the factory meets the "5-log reduction" standard—meaning the process has successfully eliminated 99.999% of the target microorganisms.