Cheese whey is an ingredient used in infant formulae manufacture. Before addition, the cheese whey is fully demineralised using Ion Exchange (IE) technology. Investigation of the IE process revealed low lactose yields. The objective of this thesis was to provide an understanding of the mechanism causing these low yields. This understanding may be used to improve these yields during IE processing. Two mechanisms were proposed for the removal of lactose during IE processing namely resin entrapment and lactose mutarotation adsorption. Investigations of the mechanisms were performed with both continuous and batch benchtop methods. Whey, lactose and DMSO/lactose feed solutions were employed with various resins. DMSO/lactose solution experiments were inconclusive in determining the mechanism. Whey and lactose trials revealed lactose adsorption occurred predominantly onto the macroporous anion resin (0.09 g-lactose/g resin) compared with the gel cation resin (0.04 g-lactose/g resin). In comparison the maximum lactose adsorption onto an alternative gel structured anion resin was shown to be 0.05 g-lactose/g resin. Absorption isotherm results were dependent on the supernatant concentration. The majority of lactose adsorbed onto both the macroporous and gel anion resins was recovered with six and three equivalent volumes of water, respectively. The adsorption dependency on the resin structure and supernatant concentration coupled with the recovery of adsorbed lactose with water proved that the resin entrapment mechanism was causing the low lactose yields. In hindsight the DMSO results were also consistent with the resin entrapment mechanism causing the low lactose yields. It is recommended that to reduce lactose losses during IE processing by 43%, gel structured anion resin (A847S) should be coupled in series with the existing gel structured cation resin (C100H). The gel anion resin would also halve the anion water requirements during lactose recovery flushing.