There are basically two different types of cooking ovens, the conventional type oven, and the convection oven. The conventional type, as its name implies, has been around for centuries, basically evolving in the method used to heat the baking chamber, as the original cooking stoves that were fueled by a wood fire inside a firebox were equipped with a neighboring chamber designed with a large door opening up to the full size of the oven front for inserting and removing large baking dishes inside it. But with the heat generated from only the side where the firebox was, it was impossible to get an even heat throughout the oven chamber, so you had to constantly rotate the pots around in order to get the baked food as evenly cooked as possible.
Then new technologies emerged first from the introduction of electricity, followed by gas. The heating elements and gas burners made it possible to have a stationary heat source rising up from the bottom and permitting a more even heat distribution inside the oven. But even with those newer developments, conventional ovens can still have warmer or cooler air pockets than the oven temperature is set at, thus the necessity to still have to rotate the dishes to prevent the food in the back from being burnt while the food in the front is barely done.
This has finally been overcome with the introduction of convection technology. By definition, convection is the process by which heat is transferred by the movement of a heated fluid such as air where the lighter density air molecules (once heated) replace the heavier density cooler molecules and move them around inside a room or a chamber (oven). This natural gravitational phenomenon of density variations combined with fan-forced movement of air by a fan creates a "forced-convection" which is the very basis of the convection oven technology.
1) - How convection works.
A convection oven offers the user the option of using the oven with maximum air circulation around the food by setting it on “convect”, while also keeping the ability of conventional baking by setting it on "bake".
The conventional oven per design is equipped only with one heating element for baking which is placed on the floor of the oven chamber, and one broiling element which is secured to the chamber ceiling used for broiling and for self-cleaning when the option is there. The chamber is also fitted with a temperature sensor probe which tells the control board when the temperature has reached its setting. Once the air molecules become lighter in density with the heat, they gravitate towards the top of the chamber while the cooler and denser molecules move down to be re-heated and continue the cycle. That is all the air movement present inside the oven, thus leaving some pockets of air hotter or cooler than the oven setting.
The convection ovens, on the other hand, are fitted with three different levels of heating elements. It still operates with the bottom element, which comes on for a preset amount of time as soon as the oven is set on "convection" and turned on. But it is also fitted with one or two top elements—one of them used for cooking, the other or both top ones used for either broiling or self-cleaning. So once the bottom element has run its preset time, it goes off and the top baking element is then activated by the same preset timer, also for the same period of time, then shuts down for the third or convect element to come on to keep generating more heat.
This third heater, secured within a double wall partition in the back of the chamber is usually formed into a circular shape. It powers on for the preset amount of time as the 3rd part of a full cycle, before shutting off and reactivating the bottom element to repeat the cycle over and over again until it reaches its set temperature. This circular element, however, is not visible from inside the oven chamber, as all you can see inside the back wall is a round opening with a fan inside of it which is further covered by a deflector designed to redirect the airflow from its center and along the back wall to create the desired airflow all around the oven chamber, thus converting the oven into a “forced-convection” oven or simply convection for short.
From the second the oven is activated on “convection”, the convection fan is powered up to initiate the airflow. The convection fan must not be mistaken with the circulating fan located outside the oven box to ventilate the warm air around the oven’s exterior walls to cool down the surroundings. The convect fan will run until the oven is turned off or the door is
2) - Convection drawbacks.
Although convection seems to solve all baking and roasting issues, it does have certain drawbacks, especially when it comes to baking. Therefore the necessity for convection ovens to include options on the control panel such as a “bake” or “thermal bake” mode that functions the same as a conventional oven, because the air circulation generated by the convect fan tends to cook the outside of baked goods faster than the middle. The time needed to get the middle properly done can be great enough for the top of the cake or pastry to flop over and dry out. Most convection oven fans, however, have variable speeds, running at high speed for a roast and a lower speed for cookies or pies, and food dehydration.
3) - How to Use a Convection Oven.
The uniform distribution of heat inside a convection oven makes for faster cooking times besides creating an even golden browning on the end result. Therefore, when you want that chewy chocolate chip cookie with golden crisp on the edges, or a moist roast crisp on the outside, convection baking or roasting is the solution of choice, and overall, it delivers great results for most types of baking. You can also place multiple (2 or 3) racks in at a time to bake many more pans at a time without having to rotate the pans for even cooking. But faster cooking times, however, will translate in reduced cooking temperatures as well as shorter cooking times to accommodate for comparable results.
A) - Therefore, a rule of thumb for reducing the baking temperature for bread, pies, or other pastries, is to reduce the oven temperature by 25°F (14°C) while baking for the same allotted time. So if a recipe calls for baking in a conventional oven at 350°F (177°C) for 1 hour, you’ll have to convert and bake at 325°F (163°C) for 1 hour.
B) - When roasting meat, the rule of thumb is to maintain the baking temperature and to reduce the cooking time by 25%. You can then cook at 350°F (177°C) but reduce the cooking time by 25% which will result in a cooking time of 45 minutes.
C) - The combined method of reducing both the temperature and the time for cooking casseroles, potatoes, and other baked foods. The rule of thumb then would be to reduce the temperature by about 20°F (11°C) and the time by 10 to 15%. So the same example would translate into 330°F (165°C) for 50 to 55 minutes (approx.).
Lastly, you should choose bakeware with low sides without overcrowding the pan to allow for unobstructed and free airflow around the food.
4) - When to use it and when not to.
As hard as it might be to believe, there are times when you don’t want that much hot airflow around foods such as any type of delicate batters such as Quickbread, cakes, delicate pastries, and soufflés to name a few.
There are numerous foods, however, that will give great results in the convection oven such as roasted meats and vegetables, casseroles, pies, cookies, etc. The hot air evenly flowing around the food will result in evenly cooked dishes crispy browned on the outside.
5) Evolution into convection steam ovens.
Just like any other technology, innovations in cooking remain an ongoing process continually evolving towards solutions for problematic issues of existing problems such as providing more moist and flavourful results with more even browning and shorter cooking time. The convection “steam” oven is such a technology and is actually becoming increasingly popular in today’s marketplace.
But like with everything else that is new and innovative, it creates a marginal increase on the price tag—up into the $5000 range. It is a convection oven combined with a steam oven and especially excels also with more delicate baking and tops it all with slower cooking time. But the question to ask yourself is: What’s the best oven for “the way I cook?” and find out how each individual convection oven cooks the food you like to cook—so is it worth the extra cash?—as overall, a convection oven works great for most meal preparation.