# How does an oven cook food?



## advoca (May 15, 2006)

How does an electric oven cook food?
 
Obviously if I put meat and vegetables in a casserole with a lid, the food inside is heated and cooks by simple heat.
 
Obviously, if I put meat on a BBQ or under the grill (broiler) the meat is heated and cooked by radiated energy.
 
But if I put a leg of lamb into an oven how much is it cooked by the hot air inside the oven and how much by radiated heat? 
 
And what is the effect on pastry? Is it cooked in an oven by just plain hot air or is there some radiated heat as well? What causes the pastry to burn? Excess heat? Prolonged heat? Radiated heat?
 
What effect does the circulating fan have?


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## Haggis (May 15, 2006)

> But if I put a leg of lamb into an oven how much is it cooked by the hot air inside the oven and how much by radiated heat?


I would say that the amount of radiated heat in an oven depends on the nature of the oven. In the case of an electric oven, as you have brought up, it would depend if the heating element is covered or not (or placed inside a compartment seperate to the main body of the oven). If it is covered then I would say that the heating of the air would be responsible for nearly all of the cooking process. If the element was uncovered, then it would probably be a combination of both hot air and radiated heat.

I know one oven-manufacturer has come up with a type of oven that cooks food by primarily using light, rather than relying on heated air. However it actually seems that it is largely bogus, I just found this Light Oven.



> And what is the effect on pastry? Is it cooked in an oven by just plain hot air or is there some radiated heat as well? What causes the pastry to burn? Excess heat? Prolonged heat? Radiated heat?


Pastry is no different to any other foodstuff being cooked in an oven, whether it is being cooked by radiated heat or hot air. What causes pastry to burn would probably be the removal of too much moisture through evaporation. Once enough moisture is gone I'm guessing the pastry has no further way to remove heat (the evaporating water would carry heat away, cooling the pastry) so the burning begins. In this case it is a combination of two factors; heat and time. The amount of time the pastry (or any food for that matter) spends in the oven must be in correlation with the amount of heat being used.



> What effect does the circulating fan have?


Not all ovens have this fan. Those that do are called fan-forced or convection ovens. This fan is responsible for circulating the hot air inside the oven to distribute it evenly throughout the whole oven. This prevents hot air simply rising and sitting at the top of the oven. Often you can reduce the temperature and cooking times when using a convection oven when compared to a conventional oven.


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## Andy M. (May 15, 2006)

Grilling and broiling are direct heat cooking methods, that is they cook almost entirely by radiant heat.

Baking and roasting are indirect heating methods that rely entirely or almost entirely on convection currents in the oven to do the cooking.  When the heating element gives off heat, the air nearest the element gets very hot and rises toward the top of the oven.  That's a convection current.  as it rises, it gives off heat to the cooler surrounding air.  This hot air transfers heat to the food, raising its temperature and causing it to cook.  

The fan in a convection oven circulates the air in the oven and causing the temperature of the air to remain more uniform, resulting in faster and more even cooking.

What causes a baked good to burn is an excessive increase in temperature.  Bottoms of foods burn because the baking pan heats up and transfers heat to the food, increasing its temperature and causing it to burn.


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## advoca (May 15, 2006)

Many thanks, all, for your info. Much appreciated.

But, a final question. When should I use the fan?


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## Andy M. (May 15, 2006)

From what I've read, a fan works best with baked goods.   Cakes, cookies and such seem to benefit more from a convection fan than, say, a roast lamb or chicken.


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## Haggis (May 15, 2006)

You can use it with everything without fail however as Andy M mentioned, it does work better with some things. He is spot on with baked goods benefiting, however puff pastry really benefits from using a convection oven.


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