Incorporating a microwave booster oven with your existing convection system can increase production capacity to meet increased customer demand and, at the same time, reduce overhead and labor.

Improving production throughput and line efficiency is a constant goal for meat, poultry and seafood processors. Significant advances are on hand and are available to processors using their own current equipment coupled with microwave booster ovens. Booster ovens can be used to preheat product centers before passing the product through the primary heating system, resulting in faster cooking and greater volume while at the same time improving product quality (figure 1).

The microwave booster ovens utilize the principles of advanced microwave energy to preheat the entire product simultaneously, including its center, so that less time and energy is required to achieve desired internal temperatures of the final cooked product. After the product passes through the microwave oven on a continuous belt, the internal temperature and surface temperature increase by the same amount, which depends on belt speed, microwave power and the volume of product on the belt. Some operations in the meat and poultry industry have seen a 50 percent to 100 percent increase in volume by adding a microwave booster oven to their present cooking systems (figure 2).

A good example would be heating marinated chicken breast. With an unaided, more or less typical cooking system, the product must be heated for a significant period of time before the internal temperature rises to reach 80 to 100°F (26 to 38°C). During this time, the high-temperature cooking environment must be applied to the surface of the product. This results in initial denaturation of surface protein with subsequent moisture loss. However, if the product is first heated in a microwave booster oven, taking its internal temperature from 35 to 40°F (1.6 to 4.4°C) to an internal temperature of 80 to 100°F, the internal temperature of the chicken breast is already 80 to 100°F when it enters the high-temperature cooking environment. The amount of time the chicken breast is exposed to the high-temperature cooking environment is reduced; likewise, the amount of time required to heat the chicken breast to its final product temperature is reduced.

Preheating in the microwave booster oven minimizes the total time required with already installed cooking systems. In plant testing of batter-and-breaded chicken breast pieces (figure 3), the total cooking time in a fryer after the chicken portions were preheated in the booster oven was reduced from 2.5 min to 1.3 min. At the same time, the oil temperature was reduced from 400°F (204°C) to 390°F (199°C). In this operation, the chicken breast was floured before passing through the booster oven, then batter-and-breaded before cooking in the fryer. An evaluation of the cooked product following the booster oven addition showed:

• A more desirable golden brown color was developed. By comparison, a slightly burnt breading look was noted when only the fryer was used.
  
• Superior batter adhesion was observed on the cooked batter-and-breaded chicken breast.
  
• The muscle retained more moisture and had improved overall quality characteristics.

In addition, incorporating the microwave booster oven in front of the batter-and-breading step before the fryer resulted in a more than 60 percent production output increase. Other benefits included lower oil temperature, shorter time in the fryer, and increased shelf life of the oil, providing a saving on oil costs. Similar results were obtained in plant trials with meatballs and roasted turkey tenders when they were preheated in booster ovens in front of air-impingement ovens.

Improving Cooked Yield

When used with conventional process heating equipment already in place at plants, the microwave booster oven has shown yield improvements of 4 percent to 5 percent with meat and poultry products. When you factors in the raw materials costs of $1 to $2.50 per pound, the potential benefits are obvious. The extra yield also means obtaining an extra 4 percent to 5 percent cooked product weight through the system. Preheating beef patties and pork sausage patties has demonstrated the process.

In one example, beef and pork sausage patties were weighed, placed on the booster oven belt and preheated 90 to 100^oF (33 to 38^oC). The patties were weighed again after preheating and did not show any weight loss. Most weight loss in meat and poultry products occurs after denaturation of the protein starts (normally at temperatures of 125 to 140^oF [52 to 60^oC]) and continues as the temperature increases. Using booster oven preheating, however, the internal temperature of the product is warmed without denaturing the surface protein and driving off the moisture. Then, as the product goes into the air-impingement oven, the surface of the product is exposed to the high heat of the oven (which denatures the protein and subsequently releases the moisture) for a shorter period of time. Because the internal temperature is already 90 to 100^oF, it takes less time heating the surface in the denatured state to reach the final targeted internal temperature (figure 4).

The net result is that cooking loss is reduced and yield is improved. Not only is this important from a yield and cost standpoint, but also for product quality. Very often, precooked products are dry after they are reheated by the consumer. By exposing the surface to lower temperature and/or a shorter heating time, more moisture is retained in the cooking process. It yields a more moist and higher quality reheated product.

Another benefit is the efficiency of the microwave booster oven in the utilization of energy. During operation of the booster oven, the stainless steel surfaces are cool to touch and in many applications do not require any air exhaust. This means you are not heating up the metal or the room, nor are you exhausting hot air or steam.

Operation and Design Simplicity

There are basically three variables in operating a microwave booster oven:

• Consistent control of the weight of product added to the belt.
  
• Belt speed.
  
• The amount of microwave power.

On some systems, the control box is set up with a touch screen that allows easy setting of the belt speed and microwave power. The actual operating belt speed and power output appear on the screen for monitoring settings. Different settings can be programmed into the control box to simplify operation, ease of starting, and changeovers. Special programs are included for startup, shutdown and safety considerations (figure 5).

Some microwave booster ovens have an easily cleaned design and an open interior that does not have heating elements or air ducts to remove and clean. Some designs use an easy-to-clean modular plastic belt. The heating cabinet is short considering the amount of energy applied to the product. It has a small footprint that allows it to be placed in front of batter-and-breading applications, fryers and air-impingement, spiral or convection ovens. In addition to preheating of meat and poultry products, microwave booster ovens have shown interesting results in the preheating of egg rolls, potatoes and peanuts, and with some applications for drying cheese and other products. PH

Links

• Ferrite Co. Inc.