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It comes down to how the heat is distributed. Both convection and conventional ovens are powered by gas or electricity. But the heat source in a conventional oven is stationary, usually radiating from the bottom, while in a convection oven a fan circulates the hot air around the chamber.
Convection ovens allow for even, fast cooking because the temperature stays more consistent, whereas conventional ovens can have pockets of warmer or colder air. Hot air rises, so when cooking food on both racks, dishes on the bottom rack may undercook while the food on top burns, explains Allison Eckelkamp, media representative at General Electric.
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Howdy!
All food(actually, all substances), have a "still" boundary layer surrounding them, which has a small insulating effect, thereby reducing heat loss or gain.
So far as situations taking place in our normal atmosphere, if a current of air is allowed to blow against this surface, it will blow away that "still air" boundary, and expose the surface, directly, to the temperature of the...+READ
Howdy!
All food(actually, all substances), have a "still" boundary layer surrounding them, which has a small insulating effect, thereby reducing heat loss or gain.
So far as situations taking place in our normal atmosphere, if a current of air is allowed to blow against this surface, it will blow away that "still air" boundary, and expose the surface, directly, to the temperature of the surrounding air.
Since there is less "insulating" effect, the surface will change temperature more quickly than had the boundary layer stayed intact.
As the surface changes temperature, on your roast, for example, it will then allow more heat to be "conducted" toward its center, until the whole roast becomes the same temperature as the surrounding air(if you leave it in the oven too long).
All the convection process does, is break down that "still air boundary", and expose the food to hot air more quickly than would happen in a standard oven.
Incidently, ALL ovens are actually convection ovens, to some extent, since they depend on heat being "conveyed" by the warm currents of air produced by a heating device(element or burner), located in the bottom of the oven.
This process, of using a forceful stream of air to break down a boundary layer, also happens in your freezer, but the flow of heat is FROM the food, into the moving air, which is colder.
The phrase; "heat rises" is actually incorrect, since what actually happens to air, when exposed to a higher temperature heat source, is that the molecules become further apart, creating a less dense form of air, which "floats" on the colder/denser air lying at lower levels.
All ovens have "spots" in them that are hotter than other locations, since the air most recently in contact with the heating device will be hottest, and the air which has been out of contact with that heater longest, will be coolest.
The stronger the force of the moving air, the more rapidly the boundary layer will be removed. Older concection ovens had VERY POWERFUL fans, which did the job a bit too well for baking, although roasting was much quicker.
They were also MUCH louder than present-day ovens, which are so quiet in the convection mode, that it's almost impossible to tell the oven is on. I've had both and like the present, quieter compromise, much better, from both a noise standpoint, plus the fact that all my cookies, pies and other baked goods are looking MUCH better than with the older convectiion type, where I had to cover baking goods with a cookie sheet, to prevent burning them.
If you've ever watched water, at a "rolling boil", in a pot, you can actually watch that natural convection taking place, since the water is being "rolled" from the center, upward, then down the outside , where it cools slightly, and drops to the bottom, then toward the center again as the heating/rising process is repeated.
There's nothing magic about this process, as most substances become less dense as they are heated.
In all heating process, we are just using natures law that allows heat only to flow from a higher to a lower temperature.
It never flows from colder to warmer.
Nature is always coasting downhill. So does heat.
Convection ovens, with a standard option, are a great way to go.
Thanks for your time.-COLLAPSE
It's not just evening out temperature by circulating the air. At least as important (probably moreso), the moving air in a convection oven increases the effective heat transfer coefficient between the food and the warmed air. This results in faster heating cooking at the same set temperature.
I learned French pastry making at the Lenôtre school for dedicated amateurs in Paris. We always used convection ovens. The lead pastry chef/teacher advised us to increase our home (conventional) oven temps by 20°F over those in the recipes, which were designed for convection ovens.
On the other hand, the second Lenôtre pastry chef says there`s no need to adjust temps, just watch the cooking...+READ
I learned French pastry making at the Lenôtre school for dedicated amateurs in Paris. We always used convection ovens. The lead pastry chef/teacher advised us to increase our home (conventional) oven temps by 20°F over those in the recipes, which were designed for convection ovens.
On the other hand, the second Lenôtre pastry chef says there`s no need to adjust temps, just watch the cooking speed. And a pastry chef/prof at a more informal cooking school in Paris, l'Atelier des Sens, says conventional ovens are better for pastry.
When I replaced my old electric oven, I went for a Frigidaire "professional series" stove with convection oven and love it. I get much more even cooking with it than with a conventional oven.
The one stupid thing about it is that they call it "professional" series but dumb it down. On convection mode, if you set it to 350 degrees, it actually runs at 340. This cannot be adjusted. Frigidaire assumes its "professional" customers are too stupid to adjust temp or cooking time for the difference between oven types.-COLLAPSE
zuriga1...
I don't have the exact answer, but I do know that some "convection" ovens do not have a heating element within the fan. Those that do would perform better.
Are the common 'fan ovens' in the UK, exactly the same as a convection oven? I have one and like it, but it doesn't seem to do cakes quite as well as the conventional ones I had in the U.S.
I have a convection oven and I LOVE it!! I cook everything in it (including souffles) and all I do is reduce the temp for the recipe and check it earlier. It makes the best roasted turkey in record time. I use a in/out thermometer which tells me the temp of the oven and of the food, so I adjust it accordingly. The convection oven is usually about 30 - 40 degrees hotter than the setting.
I remember something about convection being bad for souffle. I think cakes would be fine though, so long as you start checking them a little earlier.
Are there items which should not be cooked on convection, but only the regular setting of a convection oven? For example, cake mixes have precise times for regular ovens - do the times have to be adjusted if convection is used, and might it sometimes brown the outside too much if the recipe isn't intended for it?
So what's an invection oven?