Cryoconcentration technology was successfully used to produce milk whey concentrates. Effect of cryoconcentration stage and thawing mode on process efficiency and physico-chemical characteristics of the concentrated and ice fractions were studied. It was found that the effect of the cryoconcentration stage was significant, whereas the thawing mode had no effect. Microwave-assisted thawing mode was an efficient procedure and was faster than gravitational mode. Whey concentrate with 37.72 +/- 0.69% of total dry matter was obtained. Proteins were concentrated up to 6.49 +/- 0.31% (w/v). The concentrated fraction was rich in potassium ions. To achieve high process efficiency, the whey should be completely frozen and thawed in three cryoconcentration stages because the process efficiency drastically decreased at the fourth cryoconcentration stage, because of high dry matter content of the frozen solution obtained in the preceding stage. (C) 2008 Elsevier Ltd. All rights reserved.