The invention concerns a process for extracting hemicellulose from fiber, such as corn fiber. The process comprises agitating at least fiber, caustic and optional added water at a moisture content from about 10% to about 60% at high speeds in a highly fluidized state. The process substantially instantaneously extracts the hemicellulose from the fiber. Heat may be applied in the process to extract and dry the hemicellulose substantially simultaneously.