Spray drying of whole milk
Processing of whole milk into powder can be done in different drying systems, but the drying system also sets the limits of the quality and type of whole milk powder that can be produced. It is important to define very early in the project, which type of end product the plant has to produce, as that will decide what type of spray dryer that has to be used. Often the plant has to be flexible enough to produce all kinds of product structures.
When milk - with 87-90 % water - has to be processed into powder it is first passed through the evaporator. Prior to the evaporation the milk undergoes a heat treatment/pasteurization to "tailor-make" the final powder to a certain specification. In the evaporator, approximately 90 % of the water is recovered. The resulting milk concentration typically with 48-50 % solids is then passed on to the subsequent spray drying operation.
The powder structure
The powder structure is categorized within the terms:
- OWMP (ordinary whole milk powder) is a standard whole milk powder without any powder structural features and is typically a powder with high bulk density. The powder can be pro-duced on most drying systems.
- AWMP (agglomerated whole milk powder) is an agglomerated whole milk meaning that the powder particles have undergone a structural change by applying fine powder particles from cyclones or bag filters on the surface of the larger powder particles, while being semi-dry. The agglomerated whole milk powder will have better solubility and a lower bulk density than the ordinary whole milk powder.
Agglomerated whole milk powder can be manufactured on most drying systems, but requires a fines return system. The agglomerates from the different drying systems will no be identical and will have different mechanical strength. The
MSD™ or the
IFD™ is usually selected.
- IWMP (instant whole milk powder) is whole milk powder, which is instantly soluble in cold water. The instant milk powder is an improvement of the agglomerated whole milk powder and requires the powder agglomerates to be coated with lecithin. Typically the lecithin is applied, either directly on the powder in the fluid bed, or when the powder leaves the back-mix bed.
Spray drying of skim milk
The categorizing of skim milk powder is based on the powder structure and the heat classification: low heat – medium heat – high heat powders. The heat classification is done in the evaporator.
The powder structure is categorized within the terms:
- OSMP (ordinary skim milk powder) is a standard skim milk powder without any powder structural features and is typically a powder with high bulk density. The powder can be produced on most drying systems.
- ASMP (agglomerated skim milk powder) is an agglomerated skim milk powder meaning that the powder particles have undergone a structural change by applying fine powder particles from the cyclones or the SANICIP™ bag filter on to the surface of the larger powder particles, while being semi-dry.
The agglomerated skim milk powder will have better reconstitution properties and a lower bulk density than the ordinary skim milk powder. Agglomerated skim milk powder can be manufactured on most drying systems, but requires a fines return system. The ag glomerat es form the different drying systems will not be identical and will have different mechanical strength. The MSD™ or the IFD™ is usually selected.
Spray drying of sweet buttermilk
Sweet buttermilk is evaporated and dried like skim milk. However, as it has a high content of lecithin, the solids content in the concentrate from the evaporator is kept at 45 % to avoid too much powder deposits in the drying chamber. Buttermilk is typically dried as a non-agglomerated powder, and like skim milk any GEA Niro spray dryer can be used.
Acid buttermilk as discharged from the traditional butter production – using acidified cream – has a pH of 4.6. It can be evaporated to a solid content of approx. 30 % and dried. Due to the high lactic acid content in the product, it is important to keep the dryer inlet air temperature low and the residual moisture content in the powder low as well, in order to avoid too many deposits in the drying chamber.