The Bournville factory first opened in 1878 with about 200 people working there. By the early 1900s the workforce had grown to about 5,000.
When the cocoa arrives at the Bournville factory, it is already in the form of a dried crumb, which is then ground and mixed with coca butter and flavourings.
The semi-liquid mixture is then mixed to develop the required flavour, removing unwanted flavours and reducing the viscosity of the chocolate.
The liquid chocolate is then "tempered", which means mixing and cooling it under controlled temperatures. This ensures the fat in the chocolate crystallises in the most stable form.
Tempered liquid chocolate is poured into bar-shaped moulds, shaken and cooled before continuing to the high speed wrapping plant.
Before packing, the moulded chocolate bars are checked for appearance, shape and weight.
The familiar purple and gold colours were introduced to the Dairy Milk packaging in 1920.
Enough Cadbury Dairy Milk is sold each year to cover every Premiership and Nationwide football league pitch five times over.