Malt syrup is made from a combination of germinated cereal grains, preeminently barley, and ordinary cooked grains. It’s among the most ancient and versatile of sweetening agents, and was the predecessor of modern-day high-tech corn syrups. Along with honey, malt syrup was the primary sweetener in China for 2,000 years, until around 1000 CE; it’s still made in both China and Korea.
Malt syrup had the advantage that it could be made in households from readily available and easily stored materials, the same whole grains that were grown as staple foods, including wheat, rice, and sorghum. It was therefore a far more affordable sweetener than cane sugar.