From liquid to solid.
Today, when we talk of chocolate, we mean solid chocolate bars. That's not always been the case. For over 2,000 years, chocolate was mainly known as a drink. The native inhabitants of Central America already drank chocolate, although it tended to be bitter. At the end of the 16th century, the Spanish made the first alteration to their recipe by adding sugar.
The next important improvement came after Dutch inventor C.J. van Houten developed a method for producing cocoa powder. This inspired the chocolate makers at Fry & Sons to take the cocoa butter removed during the process and mix it with the chocolate liquor. The result was a ductile, smooth mass which was easy to pour into a mold. The chocolate bars thus created were a huge advance in terms of quality compared with their rather dry, brittle precursors.
But there was still room for improvement. 1876 saw the first steps in the rise to dominance of Swiss milk chocolate, produced by D. Peter using the powdered milk invented by H. Nestlé. In 1879 chocolate was given the soft melt-in-the-mouth effect we know today thanks to the principle of conching, invented by R. Lindt. This gave the chocolate liquor a particularly smooth consistency. Chocolate produced in this way was known as “fondant chocolate” to clearly distinguish it from chocolate produced “normally”.