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.
- 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.
Improving Cooked YieldWhen 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 100oF (33 to 38oC). 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 140oF [52 to 60oC]) 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 100oF, 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 SimplicityThere 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).