A METHOD OF PREPARING A LACTULOSE CONCENTRATE BY EQIMERIZATION OF A HOT AQUEOUS LACTOSE SOLUTION WHICH COMPRISES ADMIXING A HOT AQUEOUS CONCENTRATED SOLUTION OF LACTOSE WITH BETWEEN ABOUT 0.05 AND 0.5 MOL OF AT LEAST ONE SULFITE SELECTED FROM THE GROUP CONSISTING OF ALKALI SULFITES AND ALKALINE EARTH SULFITES PER KG. OF LACTOSE MONOHYDRATE CONTENT OF SAID LACTOSE SOLUTION, AND MAINTAINING THE ADMIXTURE OF SAID SULFITE AND SAID LACTOSE SOLUTION AT A TEMPERATURE BETWEEN ABOUT 80*C. AND 110*C. TO CONVERT LACTOSE IN SAID LACTOSE SOLUTION INTO LACTULOSE.