Various methods of obtaining hemicellulose from plant sources are provided. In one embodiment, hemicellulose is obtained from plant hulls by first jet cooking a plant hull slurry to remove starch from the plant hulls, and subsequently jet cooking the destarched plant hull slurry to extract a solubilzed hemicellulose. In an alternative embodiment, hemicellulose may be obtained by forming a plant hull slurry, adding sufficient lime to enable starch gelatinization and separation of hemicellulose in a single jet cooking step, jet cooking the slurry, and separating solubilized hemicellulose from insolubles. Surprisingly, the yield of hemicellulose is high, and the starch from the plant hulls will gelatinize but will not become hydrolyzed, such that the formation of reducing sugars is substantially avoided.