It's unlikely you've ever used maltose in your kitchen, but you've almost certainly eaten it in Peking duck, mooncakes or Chinese sweets.
What is it? A sugar produced by fermenting germinated grains such as barley, rice and millet. Although it's also known as malt syrup, it doesn't have a syrupy consistency. At room temperature it's so thick as to be almost solid but, when it's heated, it becomes a little more fluid.
How is it available? As a syrup (sold in small tubs) or a powder (in boxes). In China, vendors sell maltose 'lollipops' and fruits glazed with maltose solution. It's also used to brew beer.
What else? The flavour is not as sweet as more conventional sugars. Most recipes call for molasses, honey or brown sugar as a substitute for maltose, but none of them taste the same or come close in terms of consistency.
How to use: maltose gives the skin of Peking duck a high gloss and a hint of sweetness. (It's used on mooncake 'skins' to create the same effect.) Peking duck is not the easiest dish to cook at home because, ideally, it should be roasted hanging from its neck to allow the excess fat to drip out. It's made by removing fat from the duck before inflating it with a pump. This separates the skin from the flesh (which makes the skin crispier when roasted). Boiling water is then poured over the duck to tighten the skin. Finally, it is brushed with a maltose-water solution, hung by its neck and air-dried in front of a fan for about eight hours before being roasted at a high heat.
For an easier dish, try roasted chicken or duck livers. Dissolve maltose in some warm water with a little soy sauce and marinate the chicken livers in the solution for about 15 minutes. Dry the livers with paper towels then roast at 200 degrees Celsius. Take them out while they're still a little pink in the centre. Serve hot, warm or cold. A similar marinade - with the addition of five spice powder and a little rice wine - can be used for roasted pork spare ribs.