The origins, science and scaling of the world's favourite frozen dessert People the world over love ice cream. But they seldom consider how the frozen dessert came into being. Ice cold desserts, called 'ices', were around as far back as the 5th century BC, when the ancient Greeks refreshed themselves with snow, flavoured with honey or fruits. Although the Greek physician Hippocrates warned his patients to avoid unhealthy chilled drinks, these icy treats nonetheless enjoyed tremendous popularity. The ancient Romans were also familiar with ices. While the philosopher Seneca criticised the emperor Nero in the 1st century AD for the extravagance of having ice and snow brought from the mountains to cool his swimming pool, he seemed to have seen nothing wrong with the emperor's fondness for chilled drinks and snow flavoured with honey. But at that time, unless Romans wanted to eat their ices only in winter or high in the mountains, they needed not only to bring snow or ice to where they consumed it, but also to find some way of storing it in warm weather. This required a special sort of building now known as an ice house. Usually constructed of stone, underground and insulated with straw, these were sufficiently cold to preserve ice cut from frozen lakes and rivers in winter, or snow carried down from the mountains. Ice houses were in regular use in ancient Rome, and their growing use soon led to the development of a busy trade in snow and ice crisscrossing Europe, the Mediterranean and parts of western Asia. Yet desserts made with cold dairy products were not invented until much later. During the Tang Dynasty (AD 616-907), the Chinese made a cold, creamy concoction of buffalo milk, flour, camphor and snow. But while it was easy enough to cool milk down, this mixture proved difficult to freeze. This was simply a matter of physics. Most milk freezes at between -0.535 degrees C and -0.565 degrees C, which is below the freezing point of water; so packing it in frozen water or snow doesn't get milk cold enough to become solid. Surprisingly, the solution to this problem was salt. When salt is added to snow or ice, energy is absorbed from a container of milk, for example, set within the snow or ice, reducing the milk's temperature and creating a basic form of refrigeration or freezing. No one knows precisely when a mixture of salt and snow or ice was first used to produce ice cream. The earliest recorded references to what we know as ice cream occurred in Europe around 1530. However, it was not until the publication of a cookbook by Mrs Mary Eales in 1718 that recipes showing how to make it appeared in English. At that time, there was considerable variation in the ingredients. Milk, cream and custard were used almost interchangeably; and books of the period recommended including, for example, rose petals, caramel, ginger, lemon, chocolate, parsley and even asparagus. For many years, historians assumed that it was the aristocracy that were the main consumers of these early ice creams. During the 18th century, for example, a range of beautiful ice cream dishes were created for French King Louis XV and his court. In 1813, US President James Madison's wife arranged for ice creams to be given to guests at her husband's inaugural ball; two years later, the French writer Balzac described the lavish ice cream desserts consumed in the great houses of Paris in his novel Splendeurs et misères des courtisanes. But, especially in 18th-century Naples in Italy, in part because of the relatively easy access to snow, it was also possible for people much lower down the social scale to make, sell and enjoy ice cream. Not only were there shops and cafés selling ice creams, but there were also vendors who sold it along the public roads, and there is evidence to suggest that some families may have made it at home. However, early ice creams were still quite different from the iced treats we enjoy today. Since the milk, cream or custard was not stirred as it was frozen, it formed icy chunks, resulting in a lumpy, disagreeable texture. In 1843, however, an American called Nancy Johnson designed a hand-turned freezer, which allowed her to make silky smooth ice cream. Her invention consisted of a large container filled with ice and salt, a tightly closed cylinder for the milk or cream and a removable handle, which was rotated to stir the ice cream until properly frozen. Even with Nancy Johnson's freezer, however, it was only possible to make small batches of ice cream at a time. But in 1926 another American, Clarence Vogt, improved on Johnson's idea with his continuous freezer, which made it possible to produce ice cream on an industrial scale. The inventions of Johnson and Vogt resulted in an explosion in the output of ice cream, which pushed the price down, making ice cream available to everyone everywhere. As more companies started manufacturing their own brands, increased competition led to the standardisation of the commercial product and to more inventive varieties.