Sweet whey originates of a ley product from production of Swiss and Gouda type cheeses. The whey is what remains after the milk has been coagolated using a slight laetic acid fermentation (PH 6,3-6,5) and rennet. After the syneresis during the cheese process, the whey is drained off the cheese curd in the cheese vat. The whey is in then passed through a separator for fat and casein micelles before pasteurization cooling and storage, before further processing.



The evaporation and pre-crystillization process of sweet whey
Sweet whey is evaporated in a falling film evaporator to 60 % total solids or more followed by a flash cooling to 30 °C. The lactose, which is found in an α and a β form, thereby becomes  supersaturated and a crystallization of the α-lactose, which has the lowest solubility, starts.

The crystallization process continues in crystallization tanks, where the temperature is further decreased to approximately 15 °C, whereby the super saturation is maintained as the crystallization proceedes. Simultaneously, β-lactose is converted (due to a mutarotation) to α-lactose and 75-80 % of the lactose is crystallized. The subsequent spray drying becomes much easier.

Spray dryer from GEA Niro
Spray dryer from GEA Niro
Spray drying of pre-crystallized sweet whey concentrate
Before spray drying, the cold precrystallized concentrate is preheated to reduce the viscosity and ease the atomization. Typically a COMPACT DRYER™, a Multi-Stage Dryer MSD™, or an Integrated Filter Dryer IFD™ spray drying plant is used. During the spray drying, no more α-lactose will crystallize even though the product becomes supersaturated again, as the solids content increases. This is caused by the speed of the spray drying process and the fact that there is not enough water present in the particles to allow for further crystallization.

The resulting powder will contain the remaining 20 % lactose in an amorphous stage. This lactose can absorb moisture over time and crystallize from the atmosphere if the powder is not bagged off in proper airtight bags. To get the last lactose crystallized, the spray drying plant can be equipped with an after-crystallization belt.

The powder is then discharged from the drying chamber at 8-10 % moisture onto the belt. Here the powder has sufficient time (10-15 min) and moisture to allow for final crystallization. The powder is finally dried in a VIBRO-FLUIDIZER™.