was a 19th-century German engineer and one of the world’s major inventors of refrigeration technology. See refrigeration. Starting in the middle of the 18th century, many people before Linde had tinkered with artificial refrigeration contraptions, but Linde was the first to develop a practical refrigeration system that was specifically designed for keeping fermenting and maturing beer cool—in Linde’s case, Bavarian lagers—during the hot summer months. Linde was born in the village of Berndorf, in Franconia, in 1842, at a time when warm-weather brewing was strictly forbidden in his native Bavaria; no one was allowed to brew beer between Saint George’s Day (April 23) and Michael’s Day (September 29). This was to avoid warm fermentations, which provided ideal habitats for noxious airborne bacteria to proliferate and caused yeasts to produce undesirable fermentation flavors. Both made summer beers often unpalatable. Summer brewing prohibition had been in force since 1553 and was only lifted in 1850, by which time Bavarian brewers had learned to pack their fermentation cellars with ice they had laboriously harvested in the winter from frozen ponds and lakes. There had to be a better way to keep beer cold…and that was just the challenge for a budding mechanical engineering professor like Linde, who had joined Munich’s Technical University in 1868. See weihenstephan. The basic principle of refrigeration had been understood for centuries. Because cold is merely the absence of heat, to make things cold, one must withdraw heat. Compressing a medium generates heat; subsequently decompressing or evaporating it quickly absorbs heat from its environment. Devices based on this principle are now generally known as vapor-compression refrigeration systems; apply this to a fermenting or lagering vessel, and it becomes a beer-cooling system. For Linde, the next question was the choice of refrigerant. Initially he experimented with dimethyl ether but eventually settled on ammonia because of its rapid expansion (and thus cooling) properties. He called his invention an “ammonia cold machine.” Linde had received much of the funding for this development from the Spaten Brewery in Munich, which was also the first customer to install the new device—then still driven by dimethyl ether—in 1873. By 1879, Linde had quit his professorship and formed his own “Ice Machine Company,” which is still in operation today as Linde AG, headquartered in Wiesbaden, Germany. By 1890, Linde had sold 747 refrigeration units machines to various breweries and cold storage facilities. He continued to innovate and invented new devices most of his life, including equipment for liquefying air, and for the production of pure oxygen, nitrogen, and hydrogen. In 1897 he was knighted, and from then on could append the honorific “von” to his surname. He died a prosperous industrialist in Munich in 1934, at the age of 92, and today Linde AG is a leading gases and engineering company with almost 48,000 employees working in more than 100 countries worldwide. For all his many accomplishments, Linde’s pioneering work in artificial beer cooling technology is perhaps his most enduring legacy.