<P> Up to the 19th century, bread in Europe was often adulterated with hazardous materials, including chalk, sawdust, alum, plaster, clay and ammonium carbonate . This gradually came to an end with government action, such as the 1860 and 1899 Food Adulteration Acts in Britain . America had a more difficult time ending these processes of adulteration however, as various states had varying policies regarding bread making . </P> <P> In the late 19th century, the British empire encouraged a noticeable increase in import of bread from the colonies . This was regarded as British bread despite its origins, and institutes such as the Imperial Economic Committee encouraged the consumption and trade of foods such as bread from across the empire as they viewed it as cementing Britain's position in its colonies further . Advancements in refrigeration technology and techniques also encouraged an increase in the import of bread, as it could be preserved a lot longer than before and could be transported over longer distances . Bread was transported and stored using refrigeration more than most other foods, particularly in North America, as it was a staple food in most diets, more so than other staple foods like meat . </P> <P> Bread - baking was industrialised at the start of the 20th century . Otto Frederick Rohwedder developed a prototype bread - slicing machine in 1912, and a practical machine that both sliced and wrapped bread in 1928 . </P> <P> A major change was the development in 1961 of the Chorleywood Bread Process . This used the intense mechanical working of dough, and control of gases touching dough, to dramatically reduce the fermentation period and the time taken to produce a loaf at the expense of taste and nutrition . </P>

Where did early forms of the sandwich originate