Different dry ingeredients can be mixed/blended in dry form to a homegeneous mix in a rotating drum or similar. However, some of the ingredients may only be available in liquid form, such as milk and vegetable oil. In some cases it is prefered to dissolve all the products in water, i.e. wet mixing to start from a liquid mix before processing, even if all the ingredients to be mixed are in powder form.  A liquid mix can be pasteurized and in order for the final bacteria content to be controlled.

 

What is wet mixing used for?
Today, wet mixing is used extensively in baby food production, coffee whitener, and production of imitation milk where skim milk powder is mixed with water and vegetable oil for the production of imitation whole milk powder.

What does GEA Niro supply?
In a complete processing line supplied by the GEA Group, wet mixing is typically engineered and supplied by GEA Liquid Processing. The heart of the wet mixing is done in the vacuum mixer where all the ingredients are mixed under vacuum to avoid air in the concentrate. The final mix is then homogenized in two stages before final heat treatment, evaporation and drying.

Example of a wet mix procedure
The wet mixing system is normally divided into a water soluble part and an oil soluble part. The preparation can be continuous or batch-wise. The water soluble part is done by addition of powders into milk or water in a high shear vacuum mixer to limit air in the concentrate. The mix can be circulated over a tank. Powder and hot water are continuously added to the vacuum tank, until the total batch volume has been achieved.

After dissolving all the dry ingredients, the water soluble minerals are added. Oil soluble vitamins are normally dissolved in oil in a small separate tank and then added to the oil mix tank. The pre-heated oils from oil mix tanks are then added into the product mix followed by pasteurization and homogenization, cooling, and storage. At this stage of the process the quality of the product is checked.

The plant is designed so that corrective actions are possible before resources are used for concentration and drying. In the case of continuous processing, all components (solids, fat, proteins, minerals) are added in line and adjustments are continuous to reach and maintain the correct product composition.