A process for preparing saccharide oligomers uses an aqueous feed composition that comprises at least one monosaccharide or linear saccharide oligomer, and has a solids concentration of at least about 70% by weight. The feed composition is heated to a temperature of at least about 40° C., and is contacted with at least one catalyst that accelerates the rate of cleavage or formation of glucosyl bonds, such as enzyme or acid, for a time sufficient to cause formation of non-linear saccharide oligomers. A product composition is produced that contains a higher concentration of non-linear saccharide oligomers than linear saccharide oligomers.