The Chinese have been making malt syrup for thousands of years. In fact up until the mass adoption of cane sugar, it rivaled honey for its popularity. The technique is pretty neat. It involves the “malting” — which is to say “sprouting” — of barley grain in pans of water. Once the seeds have germinated, the sprouts are dried and ground up to make a powder.
What’s the point of this? Simply that sprouted grain is rife with starch-digesting enzymes. It’s those enzymes that are responsible for disassembling the starch in the seed, which is the fuel that the sprout needs to grow. However those enzymes can be hijacked and put to other purposes…like breaking down rice or wheat starch. And that’s exactly what the Chinese did with it, creating sugar solutions out of mashed grain and malt powder that they’d boil down to thick syrups.
Malt syrup is similar to other sugar syrups in that it contains lots of glucose, maltose and other longer-chain sugars. It isn’t used all that much anymore, though bakers use it to spike their bread doughs with both sugar and enzymes.