Given the high hydration of this dough, one might expect that this dough would be extremely soft and too sticky to handle. Here’s why it isn’t: The recipe contains oats, and before adding them to the other ingredients, we soak them in some of the water (boiled first), which causes them to gel and essentially lock away this moisture. This technique is called tangzhong, and we’ve employed it in other bread recipes, but only with refined white flour.
It turns out that oats are even better at “hiding” extra liquid in a dough. That’s because, as a whole-grain product, oats contain more pentosans—a type of carbohydrate—than refined white flour, which has had its pentosan-rich bran layer milled away.
Pentosans are more absorbent than starch and can hold up to 10 times their weight in water. The upshot for our oatmeal rolls: With so much water in the dough, the rolls bake up exceptionally moist and stay that way longer.