Disclosed is a process for the production of d-tagatose from deproteinized whey or whey permeate containing lactose after acid hydrolysis to provide a hydrolysate comprising 1 equivalent of d-glucose and 1 equivalent of d-galactose for each unit of lactose converted. More particularly, the invention relates to a process for the isomerization of d-galactose to d-tagatose and the use of a simplified separation scheme based on simulated moving bed (SMB) separation. The isomerization of d-galactose to d-tagatose is carried out in the presence of calcium oxide or calcium hydroxide. The process is useful for providing a simplified processing route to providing pure d-tagatose and glucose syrup as two products from lactose hydrolysate isomerate. D-tagatose is useful as a food additive, as a sweetener, as a texturizer, as a stabilizer, or as a humectant.