In the paper, there are described conditions for bioconversion of saccharose into FOS preparations by commercial enzyme preparations (Fructozyme or Novoferm containing fructosyltransferase). The main objective of this bioconversion was to manufacture 3 FOS syrups and 2 powders containing 50%-60%, and over 90% of fructans respectively. It was proved that the transglycosylation of the fructose moiety was a three-phase process when the enzyme was applied in doses of 1.0–2.5 U/g saccharose. During the first phase, kestose is a major fructan formed (nearly 80% of the synthesized FOS). During the second stage, kestose is transformed into nystose (over 50% of the synthesized FOS). Additionally, during the third stage, a balance state among kestose, nystose and F-nystose (their proportion rates are 2:4:3) is settled. It was proved that after the glucose has been removed by an enzymatic oxidation, the nystose-rich solutions of FOS can be dried off using a spray-drying method; the dry-off process shall occur under the conditions similar to the production of powder milk. Furthermore, it was evidenced that from among all the nystose syrups containing over 72% (w/w) of dry matter, the nystose crystallizes with a little amount of kestose applied in the form of a non-hygroscopic fine-crystal substance.