Drum drying
The drum drying is a method from the process technology for drying of solutions , suspensions or pasty masses. In addition to spray drying , it is an important process for the production of milk powder .
preparation
Since the concentration of dissolved and dispersed substances in the milk increases during powder production, the milk must have a high level of stability. Otherwise the proteins can destabilize and fail. There must be no contamination with metal ions, especially copper. The germ count requirements must be observed. The milk is freed from dirt particles in the cleaning centrifuge, is cooled and then stored in a cool place. Depending on the type of powder, some or all of the milk fat is centrifuged off as cream.
This is followed by a heat treatment that has various goals:
- Inactivate all pathogenic bacteria (see pathogenicity ) and reduce the total number of germs
- Inactivating the enzymes , especially the lipase
High-short-term procedures are to be preferred, as the desired effects are achieved more gently and more antioxidant substances are formed. Likewise, the solubility of the powder is better using a high-short term process. Often the temperature is 88–95 ° C for 15–30 seconds, sometimes with temperatures up to 130 ° C.
The milk then enters the evaporation system. Water is gently evaporated under vacuum at temperatures of 45–75 ° C until a concentration of 33–35% or 40–50% of dry milk substance is reached. (The first area applies to subsequent roller drying, the second to subsequent spray drying.) In the evaporation plants, energy is used efficiently through multiple use. Thanks to the thin film technology, the milk and the resulting milk concentrate only stay in the system for a very short time at an elevated temperature.
Drum drying
Milk concentrate of 30-35% dry matter is applied in a thin layer to the rotating drying rollers. These are heated from the inside with steam and have a temperature of up to 145 ° C. In less than 3 seconds a residual water content of only 4% is reached and the dried milk is scraped off the rollers with knives. The powder leaves fall into a screw conveyor and are then crushed in a hammer mill, cooled, sieved and then packaged. In comparison to spray drying systems, roller drying systems are relatively compact and cheaper to invest. Due to the drying process, the particles are flaky and flat during drum drying.
Changes due to roller drying
When milk is drum dried, certain irreversible changes take place. The high temperatures cause denaturation of the milk proteins, a caramelization of lactose and browning through the Maillard reaction . Roller-dried powder has poorer solubility in water than spray-dried powder because of protein denaturation . For certain applications, the properties of roller-dried milk powder are advantageous, e.g. B. in chocolate production.
Individual evidence
- ↑ a b c Walter Bisig: Production of whole and skimmed milk powder. Section: roller drying. ( Memento of the original from August 30, 2011 in the Internet Archive ) Info: The archive link was automatically inserted and not yet checked. Please check the original and archive link according to the instructions and then remove this notice.
