Maltose
From Cookipedia
Maltose is a form of sugar derived from the brewing of cereals. You will probably have to visit a Chinese wholesaler such as Seewoo to purchase it as I have not seen it in supermarkets in the UK.
The production of maltose from germinating cereals, such as barley, is an important part of the brewing process. When barley is malted, it is brought into a condition in which the concentration of maltose producing amylases has been maximised. Mashing is the process by which these amylases convert the cereal's starches into maltose.