Dutch seafood marketer Roem van Yerseke is using microwave pasteurization technology to launch a line of refrigerated ready meals consisting of mussels, vegetables, and seasonings. The taste of the meal, says the firm, is comparable to the taste of fresh mussels prepared in the traditional way: steamed. But the advantage to consumers is that the 750-g serving can be prepared in the home microwave oven in less than 5.5 minutes. Also, fresh mussels have a six-day shelf life. Roem van Yerseke’s ready meals—thanks partly to modified-atmosphere-packaging technology—have a 21-day shelf life.
The launch of this new line of seafood targets several demographic groups who are difficult to reach with traditional fresh mussels. People aged 18 to 35 are too impatient to steam mussels and prefer a convenient format that goes into the microwave with no muss and no fuss. Also targeted are the elderly, who can have difficulty with the physical act of preparing mussels. And finally, preparing fresh mussels for a single-person household is impractical, so the ready-meal in a plastic tray with easy-peel lidding is suitable for singles or for families in which not all family members eat mussels.
The technology behind the launch is called MicroPast, which was developed by Creative New Food GmbH. The process engineering partner is International Packaging Systems, a part of Germany’s Schubert Group.
Micropast is essentially a variety of steam pressure cooking in which microwaves function as the source of energy. Because throughput time is in the range of 8 to 12 minutes instead of two to three hours for pasteurization in a steam oven or autoclave retort, MicroPast puts less thermal stress on the food. This leads to increased nutritional value, more attractive color retention, and better food taste and texture. In addition, raw menu components such as vegetables, fruits, and chicken/pork/fish are cooked in one step. There’s no need for pre-cooking operations, so overall prep time is greatly reduced. And finally, energy consumption is minimal.
Live mussels
The packaging/pasteurization operation at Roem van Yerseke begins with an operator emptying large boxes of fresh, live mussels into an incline conveyor. It leads to an overhead combination scale with nine buckets, seven for weighing out and depositing mussels and two for weighing and depositing vegetables.
Below the overhead scale, thermoformed polypropylene trays are automatically denested in a single file and conveyed beneath the depositing funnel that drops the mussels. A short distance later, vegetables are deposited from the same overhead scale. A separate depositor then adds a water solution with seasonings. No preservatives are involved.
Next is heat sealing of the clear lidding material, performed on a machine that does four trays per cycle and cycles 10 times per minute, so typical throughput is about 40 trays/min. Roem van Yerseke chooses not to identify tray material or lidstock, and the firm is equally guarded about machinery vendors.
Lidding material includes small punctures done in registration as well as eye marks that can be read by the lidding machine. The end result is that the lidding material applied in registration to each tray has a steam-pressure release hole through which steam can be released as the trays make their way through the microwave pasteurization tunnel. Without this release valve, pressure would build inside to the point where the lidding would burst apart from the tray. An interesting detail: The circumference of each of these punctures is reinforced with a bead so that it can withstand the process stress inside the microwave pasteurization tunnel without tearing and permitting more venting than the design spec calls for.
As trays exit the lidding machine, they pass over a checkweigher. “It’s critical that the amount of product in each tray is within acceptable parameters because the microwave pasteurization process is very precise and depends on having the right amount of mussels in every single tray,” says Johan Lacor, manager of the seafood division at Roem van Yerseke. Should any tray be over or underweight, the checkweigher catches it and causes that tray to be ejected from the line.
Trays make a right-angle turn and are metered into a collating device just ahead of the entrance to the microwave pasteurization unit, manufactured to International Packaging Systems’ specs by a German manufacturer. When six trays are in place, the collator pushes all six at a right angle into the pasteurizer, which means they travel six-across.
As the food products are heated by the microwave energy, steam is produced inside the tray. Because steam is an optimal heat conductor, no hot or cold spots are created, and high core temperatures between 90 and 95 deg C are generated inside the product in a short time.
Cooling bath
Immediately after the passage through the microwave tunnel—which is about 70 or 80 ft long—trays pass through a cooling bath. They then make a right-angle turn and are single-filed into a highly specialized piece of modified-atmosphere packaging equipment that removes steam inside the trays in a gas-injection process. Six trays pause inside this machine as six needles puncture through the lidding material right next to the steam-pressure release hole on each film lid. As cold nitrogen is introduced into the tray by the needles, steam is forced out through the steam-pressure release hole in the lidding material.
Surface temperature of the food inside the pack drops by 10 to 15 deg C. This prevents the generation of a vacuum during cooling. The six trays now index forward to a station in which both openings—the steam-pressure release hole and the small puncture created by the MAP system for injection of the nitrogen—are closed by a special label to maintain the sterile environment inside the pack. This MicroPast label plays another important role when the consumer heats up the ready meal in the microwave oven. The label is a one-way valve that lets steam and pressure vent from the container so that the tray won’t burst.
Trays exiting the MicroPast label application station pass through a metal detector and then an ink-jet printer that puts product name and a lot number useful only to Roem van Yerseke. The final piece of equipment in the line is a spiral cooler that brings temperature down even further. Consumer-facing information like best-use-by date is imprinted on a paperboard sleeve that is subsequently applied by hand.
Marketed under the Zeeland’s Roem a la minute brand, these ready meals began reaching store shelves in the Netherlands, France, Belgium, and Germany in June. Selling price is about $6.00 for the 750-g serving.
Distribution is through a local distribution company. “We have more than 30 years experience in the distribution of mussels because we go to market through the same distributors with our fresh mussels, too,” says Lacor. “With this new product we go to retailers, supermarkets, some restaurants and cafes. Small restaurants and cafes have a difficult time getting permits to prepare fresh food. This product is easier for them to serve their customers because in fact the café need only re-heat these meals, not cook them from raw ingredients.”
When asked if being among the first to commercialize such cutting-edge technology was at all unnerving, Lacor acknowledged that it wasn’t without risk. “But we had and continue to have confidence in IPS, and in fact everything is running extremely well.”
