where fragments of a jug, from between 5,400 and 5,000 years ago was found to be coated with beerstone, a by-product of the brewing process. Beer may have been known in Neolithic Europe as far back as 5,000 years ago, and was mainly brewed on a domestic scale. Beer produced before the Industrial Revolution continued to be made and sold on a domestic scale, although by the 7th century AD beer was also being produced and sold by European monasteries. During the Industrial Revolution, the production of beer moved from artisanal manufacture to industrial manufacture, and domestic manufacture ceased to be significant by the end of the 19th century. The development of hydrometers and thermometers changed brewing by allowing the brewer more control of the process, and greater knowledge of the results. Today, the brewing industry is a global business, consisting of several dominant multinational companies and many thousands of smaller producers ranging from brewpubs to regional breweries. More than 133 billion liters (35 billion gallons) are sold per year—producing total global revenues of $294.5 billion (£147.7 billion) in 2006. Early beers As almost any cereal containing certain sugars can undergo spontaneous fermentation due to wild yeasts in the air, it is possible that beer-like drinks were independently developed throughout the world soon after a tribe or culture had domesticated cereal. Chemical tests of ancient pottery jars reveal that beer was produced about 3,500 BC in what is today Iran, and was one of the first-known biological engineering tasks where the biological process of fermentation is used. Also, archaeological findings show that Chinese villagers were brewing fermented alcoholic drinks as far back as 7000 BC on small and individual scale, with the production process and methods similar to that of ancient Egypt and ancient Mesopotamia. Author Thomas Sinclair says in his book, "Beer, Bread, and the Seeds of Change: Agriculture's Imprint on World History" that the discovery of beer may have been an accidental find. The precursor to beer was soaking grains in water and making a porridge or gruel, as grain were chewy and hard to digest alone. Ancient peoples would heat the gruel and leave it throughout the days until it was gone. A benefit to heating the gruel would be to sanitize the water and the temperature required to denature grain proteins would also denature disease microbes. Leaving the gruel to sit would change it. Fermentation would