Effect of Humidity on Moisture Content and Forms of Lactose in Dried Whey

Dried whey contains 60 to 75 per cent of anhydrous lactose in the dry matter, depending largely upon the extent of lactose fermentation prior to drying. If whey is dried by the ordinary sl)ray or roll drying process in the manner customarily used for milk, the lactose does not crystallize but remains in the form of a syrup or glass. Whey dried in this manner is very hygroscopic. At ordinary humidities it will absorb moisture and become sticky, and the lactose will finally crystallize, forming a hard cake which must be broken up. The role of lactose in the caking of dried whey has previously been discussed and demonstrated by Troy and Sharp (4). Several patents have been issued covering various processes for inducing lactose crystallization prior to the complete drying of whey (i).