Convection cooking refers to cooking with the additional advantage of airflow circulation. This allows for a much more even distribution of heat. The use of forced flow of hot air helps to reduce cooking time and save energy, and the even distribution of heat ensures food are more evenly cooked in a shorter period of time.
Convection cooking uses an integrated fan to circulate the hot air around and across the food to cook them all evenly and at the same time, generally taking three-fourths of the time required in standard cooking. When hot air is blowing onto food, as opposed to merely surrounding it, the food tends to cook more quickly. Cold or partially frozen food is surrounded by a thin layer of cold, slow-moving air, which in effect insulates the food and slows down the cooking process. Forced convection cooking equipment resolves this issue by creating a very rapid convective flow that blows away the envelope of cold air surrounding the food.
Generally, a good convection oven will have three heating elements: a top, a bottom and a rear, with a fan connected to the back of the oven. As the oven pulls in outside air, it is heated immediately and circulated in the oven compartment by the fan to ensure a more even distribution of heated air for cooking.
In a steamer, the heat transfer medium is steam, which like air, is a fluid and subject to the same convective flow. As the steam enters the cooking chamber, it rises gradually, transferring its heat to the food, and then slowly falls. It is reheated and the cycle begins again, creating a circular flow. By using a fan in convection steamer to force this circular flow to occur rapidly, the transfer of heat to the food is greatly accelerated, reducing cooking time and energy consumption. In addition, the rapid circulation of the steam prevents flavor transfer from one food to another that occurs when steam condenses on the food.