When operating an electric toaster oven a student must pre-heat the oven for no less than 5 minutes to be sure the oven compartment has reached the temperature the food needs to be cooked in. On a toaster oven, there will probably be cooking choices which determine which heating devices in the unit will come on. Normally these choices are “bake,” “toast”, or “broil”. Baking cause the heating element in the bottom of the stove to warm up, broiling causes the top element to heat up, and toasting causes both top and bottom elements to become hot. When the type of heating needed is selected, the unit is on and the correct temperature must be selected.
In a microwave oven, there is no preheating necessary because the oven cavity does not heat up to cook the food. Electricity is converted to shortwaves as in a radio.
These waves penetrate and bombard the molecules of food causing them to move around rapidly. This movement causes heat which cooks the inside of the food to the outside through conduction. Since these short waves cannot penetrate metal, utensils needed to use in a microwave must be made of heat proof plastic or glassware and glazed ceramics. These utensils can be used in the microwave oven because the short waves can pass through these items to the food. Other materials (which are not necessarily utensils) can be used in the microwave such as paper towel, plastic wrap, roasting bags, and napkins because the short waves can pass through these also. When operating the microwave, food to be cooked is placed in the oven cavity, the door is shut tightly, and the oven can be turned on. Microwave ovens in proper working order cannot used if the door is open or if the seal is damaged. Depending on the type of stove, basic operations include the timing device and power levels.
The use of each depends on several factors. The length of time food cooks is influenced by the volume of the food, the density, fat, sugar, moisture content of the fond, and the shape of the food and starting temperatures.
A teacher demonstrated experiment can be conducted using two potatoes. This will illustrate the difference in the way toaster ovens will heat food and the way microwaves will heat food. Before preparing the potatoes, pre-heat toaster oven on bake at 400. Prepare the similar size and shape potatoes by scrubbing them with water, drying them, and lightly oiling them to keep surface tender.
Place one potato in the center of oven rack in toaster oven. Place the other on a paper towel in microwave. Shut the door and program 2 1/2 minutes on high power.
Remove both potatoes from ovens. Cut potatoes in quarters. Visually, students will be able to tell that the microwave potato is much hotter, although it is not completely cooked. This is an example of how microwaves penetrate food to a depth of 1/2-2 in.