The juice of lemons has been used for many centuries to produce a refreshing drink. An early problem was the deterioration of the lemons during transport. The concentration and finally crystallisation of citric acid from the lemons was first achieved in 1784 by the Swedish chemist Carl Wilhelm Scheele. Hooper in his medical dictionary of 1825 described the preparation of a lemonade dry mix using citric acid derived from lemons. The demand for citric acid increased rapidly throughout the 19th century and this continued to be met by extraction from citrus fruits, mainly in Italy (Sicily).