Food safety is a crucially important issue in the pet food industry. The EU repeatedly reports product recalls due to salmonella-contaminated animal feed, which must therefore be subjected to thorough treatments and to inspections to ensure that they are safe for consumption. Thermal processes are commonly used in the food industry to reliably kill microorganisms. When selecting the appropriate process, however, it is important to consider the effects of heat on the stability of the product to be treated.
With their patented FoodSafety-IRD (Infrared Rotary Drum), Kreyenborg, which specializes in bulk-solids, offers system components that in addition to drying and roasting food can sterilize and pasteurize bulk food or feed with greater care. Microorganisms such as salmonellae, E. coli, enterobacteria, mold or yeast fungi are killed reliably and the shelf- and storage life of the products are thus prolonged. This infrared process can also kill insects and their larvae and eggs with certainty. Germ reduction achieved by the FoodSafety-IRD corresponds to a Log5 validation.
The advantage of the FoodSafety-IRD lies in the operating principle of infrared light, conducting energy directly into the product core, heating the material from the inside, out. This is unlike other thermal processes, such as hot air dryers, which require hours to heat the product, and does it in reverse – from the outside to the inside. The FoodSafety-IRD heats the product core in a matter of minutes, resulting in significantly shorter dwell-times.
Working Principle: Rotary Motion with Infrared-Light Technology
The infrared process can be illustrated by means of a cross-sectional view:
Cross-sectional view: The rotating drum of the FoodSafety-IRD is constantly in motion, ensuring uniform exposure to the infrared light.
The pet food to be post-processed is continuously conveyed into the rotary drum by means of a feeding unit. The product is transported from the inlet through the rotary drum to the outlet via a welded-in helix conveyor and is constantly mixed by the rotational movement. Simultaneously, the material is exposed to infrared light, thus heating entire particles, and when necessary, water can be sprayed onto the product. When applied, this fine water mist has an additional sterilizing function, since bacteria reduction is enhanced at the moment of surface evaporation of the mist. This in addition creates a protective re-cooling effect. Infrared light has the advantage of being able to treat even products with a low water content.
Process Preserves Color, Taste, Consistency and Ingredients
The decisive factor for a highly homogeneous product appearance is this constant rotation and movement, as Managing Director Jan Hendrik Ostgathe explains: „In a belt-dryer, for example, the product remains in one place for a longer period of time; this can lead to uneven nests forming that promote mold growth. By contrast, the constant rotational movement inside our infrared rotary drum dries the material evenly. This gentle process preserves the color, flavor, consistency and the valuable ingredients of the product.“
The Foodsafety-IRD has four temperature zones which can be set independently according to the product, and which adjust themselves automatically, based on the recipe stored in the control system. The product temperature remains constant, and overheating is thus avoided. Depending on the desired process – in the case of pet food this would be mainly sterilization and pasteurization, but drying or roasting, as for nuts, is also possible – appropriate product temperature and dwell-time must be selected. Temperatures of 80 to 200 degrees Celsius and above can be achieved in the FS-IRD.
Stand-Alone Solution, or Integrated Module
Kreyenborg supplies the FoodSafety-IRD as a plant component for its customers, but also offers turn-key solutions. Sterilization and pasteurization usually involve stand-alone solutions, requiring the necessary equipment, i.e. upstream and downstream conveyor technology, product cooling and big-bag handling (filling and emptying). On the other hand, drying usually entails an integrated solution with upstream and downstream process steps provided by the customer.
The infrared system is individually designed after a determination of the technical requirements. In pet food sterilization, microbiology is relevant, because a microbiological protocol is required as to which impurities the product has. Other factors include the size of the product, the bulk density, the input and output moisture, and perhaps whether the product has a special ingredient that is thermally sensitive (this could be for example a product with a high sugar content).
Customizing Temperatures and Times
In the case of specific requests, where requirements involve particular temperature regulation from the FoodSafety-IRD, new solutions are sought. Jan Hendrik Ostgathe describes one: „A so-called press cake may be processed at a maximum of 70 degrees °C so as not to destroy valuable proteins. For the press cake, seeds are pressed, the oil is extracted, and what remains is a kind of cake batter that contains proteins and nutrients. Since oils and moisture are still present after this procedure, the dough must be dried to a residual moisture content of less than five percent to allow for storage and further processing. This product is used as an additive to pet foods because of its valuable nutrients. In collaboration with our customers, we often carry out trials with modified temperatures and dwell-times and then have laboratories test the effects of these adjustments on the product – in this case on the valuable protein. For the press cake, we were able to modify the temperature and drying time so that the protein was retained.”
Steam Processing Affects Product Properties
An alternative process for sterilization and pasteurization of feed is the common steam process. Saturated steam is applied to the respective product. For the process to be effective here, higher temperatures are involved, but these in turn have a greater impact on the product’s properties. The product is thus affected: the color changes, ingredients volatilize, and the overall appearance and consistency deteriorate. With the infrared process, on the other hand, product properties remain nearly unaffected. Further, infrared is a natural application that does not use gases or chemicals commonly used in other treatment processes to eliminate microorganisms. Another positive aspect of infrared light is its significantly higher efficiency due to direct energy input. Compared with a hot-air roaster, for example, which is operated with gas and has higher CO2 emissions due to combustion, the infrared rotary drum can be operated with renewably generated electricity
The time needed for cleaning after each product change is considerably reduced due to fast, easy access to the rotary drum – and thus down-times throughout the entire plant are reduced. „Flexibility is the most important feature of our infrared system,“ emphasizes Jan Hendrik Ostgathe. „Numerous products in various forms from a wide range of food sectors can be processed. The focus is on the product, and the machine is set up according to that product’s specific requirements. We often first test and develop the appropriate treatment in our in-house technical center, checking temperatures, times and product properties and then setting the right parameters in consultation with the customer.“