What is Drum Drying in Food Processing?
Food processing is how raw agricultural ingredients are turned into food. That is a simplistic answer, but the actual steps in food processing are much more complex. There are several different methods used depending on the final food product. In this article we are going to review the drum drying method in food processing to understand its history, function, and importance.
According to Van Drunen Farms, “In the drum drying process, pureed raw ingredients are delivered over two rotating, high-capacity drums and undergo a validated kill step. Sheets of drum-dried product are milled to a finished flake or powder form. Drum-dried ingredients reconstitute immediately and retain their flavor, color and nutritional value.”
HISTORY OF DRUM DRYING
The drum dryer was invented in the early 1900’s by John Augustus Just to dry milk into powder; it was later adapted to several food processes and chemical manufacturing. The intent was to dry heavy materials and manufacture dehydrated powders and flakes. Eventually, James Robertson Hatmaker, an American entrepreneur purchased the patent. Hatmaker’s team developed the modification of a scraper knife.
Today, drum dryers are used for drying viscous materials, pastes, and thick liquids, and producing dehydrated powders and flakes. Some products include milk, baby food, cereal, fruit and vegetable pulp.
HOW DOES A DRUM DRYER WORK?
A drum dryer is a continuous rotating cylinder that is heated with steam or hot water on the inside. As the drum rotates, the heat transfers from the drum surface to the wet material, causing the moisture to evaporate. The food materials pass over the drum dryer to dry it to the desired temperature. A roll cleaning blade or scraper knife is used to flake the dried material off the drum dryer.
STEPS IN THE DRUM DRYING PROCESS
Below is an overview of the four main steps involved in drum drying and how each step works to ensure consistent drying results.
STEP 1: FEEDING
In the feeding step, the wet mixture that needs to be dried such as a slurry, paste, or liquid is applied to the outer surface of the rotating drum dryer. There are different ways to feed the material onto the drum including rollers, dipping, spraying, or splashing.
STEP 2: HEATING
The drum is heated using steam, hot water, or other heat sources. This heat moves through the drum dryer’s wall to the wet material on the outside, warming it up and causing the moisture to evaporate.
STEP 3: DRYING
As the drum dryer rotates, the thin layer of material stays in contact with the heated surface. This allows the water to evaporate and the material to dry. Drying happens in three phases:
- Initial heating: The temperature rises quickly heating up the product.
- Steady drying: Water continues to evaporate with a constant temperature.
- Final drying: Once most of the water is gone, the temperature increases again to remove the remaining moisture.
STEP 4: SCRAPING OR ROLL CLEANING
A scraper, knife, flaker or roll cleaning blade removes the dried product from the drum dryer’s surface. For certain materials, especially those with high sugar content, a cooling step may be added to prevent sticking or damaging to the product.
KADANT'S ROLE
During the drum drying process, a roll cleaning blade, scraper, knife, or flaker blade is used to remove the food product evenly and hygienically from the entire surface of the drum dryer. Drum drying becomes less efficient if the blade systems do not remove the dried product due to uneven pressures and ineffective blade materials. To solve this, Kadant supplies the unique AccuFlake™ PRO blade holder and ProFlake™ roll cleaning blade designed specifically for drum dryer applications. Both products are HACCP International food safe certified. To learn more about the AccuFlake PRO blade holder and ProFlake roll cleaning blade, check out the article, “Revolutionizing Food Processing with Advanced Drum Drying Solutions.”
WHAT ARE THE DIFFERENT TYPES OF DRUM DRYERS?
As mentioned previously, drum dryers are rotating heat transfer devices used in food processing, but there are different types. The following are the two most common forms of drum drying.
- Single drum dryers: Consist of one rotating cylinder or drum. The food material is fed on to the drum surface and dries as it rotates. A scraper, knife, flaker or roll cleaning blade removes the dried product from the drum.
- Double drum dryers: Consists of two drums rotating in opposite directions. The food material passes between the drums through what is called a nip.
To learn more about the types of drum dryers, check out the article, “Types of Drum Drying in Food Processing.”
WHAT ARE THE ADVANTAGES TO DRUM DRYING?
Drum drying is intended for use for viscous materials that are difficult to dry with other methods. When used for the appropriate application, there are several advantages to using a drum dryer methodology.
- High drying rates
- Efficient use of heat
- Relatively high energy efficiency
- Simple operation and maintenance
- Preservation of nutritional compounds
- Excellent porosity and rehydration of final product
