The first patent for a microwave prepared food was filed in 1946. The patent was for popcorn popped on the cob. Today, there are many more microwavable food options than those that simply go pop – although popcorn does still top the list.

Today’s offerings include full meals – some frozen, some fresh, some shelf-stable and others even classified as gourmet – that are intended to be prepared in the microwave for consumers looking for a more convenient way to cook. A study focused on national eating trends from the NPD Group found that in 2009, 22.5 percent of all meals prepared in the home involved the use of a microwave oven.

Consumers are using microwaves to steam vegetables and cook raw proteins, as well as to reheat frozen foods. They are continuously on the lookout for convenient meal options, but are less willing to sacrifice food quality than they might have been in the past.

This means processors of microwavable meals have their work cut out for them – they have to come up with ways to develop and package convenient microwavable meals that are also quality meals. According to Sean Brady, Ready Meal technical manager for North America, Sealed Air Cryovac Food Solutions, processors must adapt product design, formulation and packaging processes to ensure high-quality and better-performing microwavable meals.

Packaging types

When microwavable foods were first introduced, there was very little microwave-safe packaging. Today, there is no shortage of microwave-compatible packaging materials. “However, differences in structure and design of those materials can impact how products perform while being heated in the microwave,” Brady says.

Microwavable packaging materials include polymers such as polypropylene (PP), Crystalline Polyethylene Terephthalate (CPET) and polylactic acid (PLA). Additionally, there are some materials considered dual-ovenable for use in microwave and traditional ovens. These packages are made from CPET, press board, folded board and aluminum materials. All materials have different pros and cons.

More sophisticated examples of packaging designed to interact with microwave ovens are self-heating technologies referred to as susceptors. Susceptors incorporate a thin layer of conductive metal into the package in order to absorb microwaves while they travel through the product or container. By incorporating susceptors into packaging, processors can target crisping and browning to particular areas of their product, such as crisping the crust of a microwave pizza.

According to Brady, susceptor packaging can serve as a key way to increase the quality of microwavable food products and is generally safe to use as long as it meets the laid out optical density (OD) specifications for metallized films.

Steaming solutions

One advance in microwave packaging that consumers have reaped the benefits from has been steam-assisted cooking technology. This occurs when the package prevents the release of the vapor that is produced during the microwaving process. By retaining this vapor, steam that usually moves away from the product is used to assist in the heating process. Packaging that has the ability to “trap” in higher volumes of steam typically has a greater effect on the food product, both when it comes to heating and eating quality, Brady says. This process also allows for more uniform, consistent heating.

One product launch using microwave steam technology that has proven to be highly successful is the Healthy Choice Caf? Steamers line from ConAgra Foods, Omaha.

“Using steam to cook is a great way to achieve a fresh taste with the convenience of a microwave,” said Tracey Parsons, spokeswoman for the product line. “Busy moms, in particular, are looking for ways to get added convenience. With steam-to-cook packaging, it also minimizes clean-up because there are no dishes or pots needed for heating.”

“Consumers told us the frozen meals they were used to didn’t give them everything they wanted,” said Rob McCutcheon, vice president of marketing for Healthy Choice. “They lacked the freshness today’s palate demands, so by taking a healthy method of cooking [steaming], and combining it with the separation technology developed at ConAgra, we were able to offer a better frozen meal.”

The Cafe Steamers line uses ConAgra’s SteamCooker technology, a tray-in-tray application that keeps the pasta and any meat ingredients separate from the sauce, allowing them to be cooked separately and allowing for improved freshness.

“The steam cooker technology…alleviated one of the challenges the frozen category faces with everything in a meal being cooked in the sauce,” McCutcheon said. “Ingredients looked the same and could get mushy. The separation technology of the tray format allows the product to be steamed more thoroughly throughout the package while cooking, allowing the vegetables to stay crisper, fresh looking and tasting.”

Three years after introducing its “steaming platform” with the launch of Healthy Choice Cafe Steamers, ConAgra continues to stay innovative in the category. Gary Rodkin, chief executive officer of ConAgra said the company is rolling out Healthy Choice Mediterranean Steamers and plans to launch another line of steaming products this summer. He said the product lines should help the company “grab a bigger piece of the very large lunch segment where we are underdeveloped.”

“The steaming platform has been a major factor in our success in the frozen meal category where we’ve grown our share more than two full points this fiscal year to date,” he said.

ConAgra used the basic steaming concept of upgrading food quality through packaging technology to create Healthy Choice Fresh Mixers in 2008 and Marie Callender’s Pasta Al Dente meals in 2009.

Packaging recognition

With a constant demand for convenience, processors are always looking for ways to meet those demands. New products and new reformulations are costly ways to satisfy consumers and bring in more sales. Another successful option is a change in packaging.

Olivieri, a division of Maple Leaf Foods and a customer of Sealed Air’s Cryovac Food Solutions, was recently honored for making such a packaging change. The company received a Silver Award at the 2011 Packaging Association of Canada (PAC) Leadership Awards for its redesign of cannelloni packaging, one of its most popular convenience meal offerings.

The product used to be packaged in a rollstock format that required items to be transferred to an ovenable container before cooking. The packaging redesign that earned accolades from PAC features Olivieri cannelloni in a Cryovac microwavable and ovenable thermoformed tray, customized with channels that allow for even distribution of sauce and separation of the cannelloni during cooking.

“This is an excellent example of how packaging can differentiate a product by increasing convenience for consumers,” said Steve Daca, sales specialist for Sealed Air’s Cryovac brand in Canada. “Olivieri has a great product, and we were excited to partner with them to expand on that by incorporating our innovative packaging solutions into their product design. As convenience formats continue to grow in popularity, we are committed to assisting our customers in creating new solutions that meet the evolving needs of the end consumer.”

Product development considerations

When processors develop a product intended for microwave preparation, there are a number of things to consider – some considerations relate to product formulation, the others to packaging.

Adapting re-heating instructions on products developed for conventional oven heating is not the way to succeed in microwavable formats, Brady says. This is because microwaves consist of electric and magnetic waves so the electrical and thermal properties of the food itself will affect the way it heats in a microwave. For example, salt has little influence on oven heating, but it can enhance a product’s ability to absorb microwaves. As a result, foods with higher salt contents will absorb microwave power more effectively and exhibit strong surface heating, he says.

Formulators must also consider if the product being cooked or reheated will start off raw, cooked and frozen or right off the shelf.

Hormel Foods offers a wide variety of microwave meals including its line of shelf-stable Compleats entrees. Hormel developed its shelf-stable technology in 1987 to provide quick, protein-rich meal solutions that don’t need to be refrigerated or frozen, and are prepared in 90 seconds in the microwave. The newest addition to the line was designed for children ages 3 to 8 – the Hormel Compleats Kids microwave meals.

According to Brady, there are a number of things to keep in mind during the product formulation process including:

  • Size of the product – The bigger the product, the more of a challenge it is to achieve a favorable reheat performance.
  • Tray shape – Tray shape can affect the way the heat flows in and around the product.
  • Product volume – It’s important for formulators to remember that microwave power coupling is affected by volume, not mass.
  • Size and shape of the product pieces – Consider altering the size and shape of meat and vegetable inclusion pieces to reduce reheat times and eliminate superheating in focus areas.
  • Addition of sauces – Sauces can be used to eliminate superheating effects in parts of the product, and can add great flavor.
  • Fat content – The higher the fat content in product components, the hotter those components will become which could lead to overheating or uneven heating.

“Developing the right microwave heating performance into products requires a balancing act of dielectric and thermal properties of product components through recipe changes and the incorporation of packaging design and product configuration into the development process,” Brady says. The best way to tackle this process is for a processor to partner its packaging experts with its microwave technology experts during the product development stage in order to develop high-quality microwavable food products. If your company doesn’t have packaging and/or microwave experts, it’s worthwhile working with some from outside the company to ensure everything is taken into account during the development process.

Brady says, “With the right partner and the right packaging processes, meat and poultry processors can offer more products in convenient formats for the microwave to capitalize on current consumer trends while ensuring high-quality products for consumers.”

Microwave magic
The physics behind microwave technologies are more complex than many people understand, says Sean Brady, Ready Meal technical manager for North America, Sealed Air Cryovac Food Solutions. Altering the amount of salt in a recipe or changing the material in a microwavable tray can completely change the way microwaves interact with food, sometimes yielding unfavorable results such as uneven reheating and cooking, he says.

Although microwaves vary in size and wattage, understanding the basic science of the technology helps processors during product development.

Brady says standard microwave ovens are composed of a few key elements, including the power supply, magnetron, microwave feed, mode stirrer and oven cavity. The power supply powers the magnetron, which produces the microwaves that are launched into the microwave cavity by the feed. Once in the cavity, microwaves can be reflected, absorbed and/or travel through materials (tray and food items). The mode stirrer, or rotation of product on a turntable, is used to change the topology of the surfaces within the cavity, allowing for more even heating of items and less repetitive and concentrated microwave patterns. Due to the position of the wave guide (feed) in microwaves, all microwaves have unique wave patterns that are not uniform or even in the microwave, which leads to uneven heating.

Magnetrons used in most domestic microwave ovens are rated up to 1,000 watts. Commercial magnetrons are rated up to 1,400 watts, are often held to higher engineering specifications, depend on using a mode stirrer instead of a turn table and are available as combination ovens with grill elements that allow for crisping and browning of products.