Fiber formation from molten fructose sugar was investigated experimentally on a spinning machine with a hollow perforated rotor. The fiberization process was visualized by a high-speed camera in different operating points obtained by variation of melt temperature and rotor rotational speed. Contours of the forming fibers were found to significantly depend on the rotor rotational speed and melt temperature, approaching involute shape with little statistical variability at sufficiently high Weber and Rossby numbers. After exiting fiberization orifices, melt jets contracted significantly and over a relatively short distance. Surprisingly, final fiber diameter rose with the Weber number due to an increase in Rossby number reducing the degree of fiber longitudinal stretching. Fiber contours were found to be initially smooth, but developing large amplitude transversal instabilities farther downstream up to a point when fiber structure is completely disrupted, creating random and highly complex new flow structures. A structure optimal for fibrous end products may be attained by controlling initial melt superheat and assuring that fibers are cooled below the glass transition temperature. (C) 2015 The Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.