Favourable reaction conditions for the enzymatic production of 1-kestose by sucrose-1F-fructosyltransferase, SFT (EC 18.104.22.168) from Aspergillus phoenicis CBS 294.80 mycelium were established. The intracellular enzyme SFT works best at 60°C, exhibits a relatively high thermostability and possesses an alkaline pH optimum. An invertase also present in the mycelium of A. phoenicis possesses an acidic pH optimum. Consequently, around pH 8.0 sucrose is converted mainly to 1-kestose and nystose while fructose is only formed in relatively small amounts. Under optimal conditions (55° C, pH 8.0 and an initial sucrose concentration of 750 g 1-1) a yield of about 300 g 1-kestose per 1.01 reaction mixture could be achieved after 8 h.