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Microwave-ready rice pudding

Rieber & Son of Norway are such big fans of microwave pasteurization as a means of extending refrigerated shelf life that they recently installed their third line.

Secondary packaging is a paperboard sleeve.
Secondary packaging is a paperboard sleeve.

A user of MicVac microwave pasteurization technology since 2006, Rieber & Son recently added its third microwave pasteurization line to its headquarters plant in Elverum, Norway. The new line is dedicated to a popular Norwegian specialty called Risengrot, a rice pudding consisting primarily of rice, milk, and vanilla that is eaten just about any time of day as either a dessert or as part of a breakfast, lunch, or dinner. By dedicating the new line to this product alone, the firm is better positioned to produce the 20 or so other SKUs in its Toro Velbekomme line of ready meals.


The MicVac method of preparing food involves a thermoformed tray filled with a mix of partially cooked and raw ingredients. A typical combination might be chicken, pasta, and broccoli. Risengrot is a little different in that it’s one precooked item, rice pudding. But the final cook/pasteurization concept applies here just as it does with other varieties. Also, the same ease of preparation is delivered to the consumer. After several minutes in the microwave oven, the product is ready to be eaten.


Onto the filled tray a flexible film lidding is heat sealed in place, but just before it’s applied, a small hole is punched in the lidstock. Over this hole is applied the patented MicVac valve, which is essentially just two pieces of PVC that are ultrasonically sealed to each other. Says MicVac key accounts manager Johan Zetterberg, “The valve looks simple enough, but in fact it’s pretty complex.”


Filled and lidded trays proceed next through the MicVac microwave tunnel. The trays are conveyed three across, and they spend, in the case of this particular product, a little less than nine minutes in the tunnel. During this cook process, the MicVac valve opens to release internal pressure created as the food releases steam. The patented valve is designed so that it can open and close multiple times.


Once the pasteurization process is complete, the trays are single filed. As they enter a spiral cooler, the MicVac valve closes. Steam trapped inside the tray condenses, which causes internal vacuum pressure to build and causes the bottom of the specially developed FlexTray to curve upward while the lidding film is pulled down towards the food contents in the tray.


The whole idea is to minimize exposure to thermal processing compared to more conventional methods such as batch retort or “sous vide” processing. Because food spends less time getting cooked, taste, texture, and nutrient retention are all optimized. Consumers can enjoy a delicious, convenient, ready meal without artificial preservatives or flavorings.

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