In order to close the technology gap between membrane technologies and spray/freeze-drying ideally with a technology that avoids thermal stress to sensitive enzyme solutions, the limits of freeze concentration for this application have been investigated. On laboratory scale it was found that average crystal sizes are > 300 mu m despite high viscosity and ice separation is possible up to 42 % solids and > 1000 mm(2)s(-1) viscosity. No activity loss was observed during concentration. A combination of two-stage freeze concentration with a filter and wash column for ice liquid separation in an integrated setup with ultrafiltration has the greatest potential and was shown to be economically feasible in three out of four cases studied.