"Brown rice syrup is made by breaking down rice starches into simpler sugars through an enzymatic reaction, straining the resulting liquid, and then boiling it into a syrup. The result is a thick, light brown syrup with the consistency of honey and the nutty, grassy flavor of cooked brown rice. It's less sweet than sugar, but definitely sweet enough to satisfy a sweet tooth...
In baked goods, brown rice syrup has much the same effect as corn syrup, which is why it makes a good substitute. A little bit of syrup will gives cakes and other baked goods a more tender crumb, a finer texture, and increased browning. Rice syrup will also give brownies and cookies a denser, fudgier texture. The flavor of the rice syrup definitely comes into play, though; I like it in recipes that use
whole wheat or other whole grain flours where the earthy and nutty flavors compliment each other."
See explanation @ The Kitchn