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Fan oven - Should I adjust temperature or cooking time?

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Initial post: 26 Sep 2011 10:02:54 BDT
baffy says:
Hi all,

I've moved house recently, and yesterday I cooked a roast beef joint in my new oven for the first time. It's a fan oven, and though I had a fan oven (or maybe fan-assisted oven) before, this one seems to have a bit more "welly" than my old one and I think I may have to start adjusting my cooking times/temperatures. Let's just say that my beef joint was "well done"!

My question is a technical one. I'm reading that "fan ovens cook at a higher temperature than conventional ovens". Is this literally true - i.e. if I set my oven to 200 does it really heat to 220/230? If so, then I don't understand why - surely an oven should heat to the temperature you set whatever kind of oven you use, otherwise why use a temperature scale? I can accept that "Gas Mark 7" might be different temperatures in different ovens, but I would have thought that 200C was 200C?!

It makes more sense to me that it would be the same temperature, but the flow of air causes food to heat more quickly. That would mean that (in most cases) I have the choice to either lower the temperature or reduce the cooking time.

The reason this is important to me is because I sometimes slow cook chicken in the oven, which needs to get to 165C/170C to be safe. I would normally set the oven to 170, but according to what I'm reading, I'm being told that I should reduce this to 150C, and I'm not sure I trust that. I don't mind reducing the cooking time, but the chicken needs to get to 170C, no lower.

I know I can just use an oven thermometer and a meat thermometer to resolve these issues for myself, and that's what I'll do, but this will only tell me about my particular oven. I wondered what the general rules were - i.e. if I use a different fan oven - what should I do?

Any help would be gratefully received! Cheers.

Posted on 26 Sep 2011 10:28:08 BDT
Kommando says:
I reduce the temp on my fan oven and then some more plus add time on as slower cooked food is juicier and holds more flavour, 150 for chicken is about right with an extra 30/40 mins but check the juices are clear between the leg and breast with no traces of blood before its finished, 20/30 mins with no foil gets the skin nicely browned. Your oven will not be exactly the same as mine so you will need to adjust to suit your oven.

The C markings on the knobs are guides only, the tolerances in the thermostat mean there is a variation and also some heating carries on for a minute or so after the element is turned off which will take it a bit higher. Its not a constant temp in an oven but like a saw blade, at its highest just after the element is switched off and lowest just after it is switched back on.

Posted on 26 Sep 2011 10:45:00 BDT
K. Williams says:
A cold chicken cools the air just a little around it, but in a fan oven the air is moving so this doesn't have the same insulating effect and the chicken will heat up hotter quicker. It's the same as when you run a hot bath - the water feels hotter if you stir you hand around. At least, that's how I think it works... We cook small chickens in our fan oven and they take just over an hour, but I must admit we put them pretty high - around 200. The meat falls off the bone!

Posted on 26 Sep 2011 15:55:12 BDT
Last edited by the author on 26 Sep 2011 15:56:02 BDT
The fan oven runs at the same temperature as a conventional oven.
BUT, the fan stirs the air around, and this has two main consequences
1. the whole oven sits at the same temperature - gone are the hot at the top, cool at the bottom zones found in a conventional oven (although sometimes very desirable)
2. the air is moving quickly over the item to be cooked, so there is no 'still air blanket' acting as an insulating layer. The heat is coupled into the food much more quickly.

An experiment; blow on your bare arm from at least a foot away - it feels cool, even though your breath is hotter than the air around you or the surface of your arm. Why? because you have removed the 'still air blanket' and also brought in an air current from the surrounding air to take away the heat from your arm. If you blow on it close-up the breath feels warm - as it should.

Does this help?

Posted on 26 Sep 2011 17:12:36 BDT
baffy says:

Thanks for all your responses. Putting them all together, what I'm getting is that the fan oven is actually the *same* temperature as a conventional oven, and when people say "200C in a conventional oven is equal to 180C in a fan oven", they don't mean that they are actually the same temperature, just that those are the temperatures one should use in each oven. So the statement that, "a fan oven is hotter than a conventional oven" is not strictly true, although it works to think of it like that.

Does that make sense?

Of course, this means that Kommando cooks his/her chicken at 150C!

It makes sense to me that the temperature would be the same but that the heat transfer is much quicker. This would suggest to me that reducing the temperature would be a good thing *a lot of the time*. This would mean that you could keep your cooking times the same and not worry about overheating the outside of the food and not cooking the inside quick enough (since the inside of the food will always cook via conduction from the outside of the food).

However, in the case of a food which *must* reach a certain temperature, you should keep that temperature, but shorten the cooking time. That's my conclusion so far.

I do understand the blowing on your arm thing, I'm just querying the whole 200C (conventional) = 220C (fan) thing. The way I'm understanding it now, what that means is that those are the temperatures one should use, rather than that those are equal temperatures.

I think I'm being really picky about this, and I'm probably over analysing it, but I just want to understand what's going on in my oven (I did Physics at uni, so I blame that)!!!

Again, thanks for all your responses. I think what I'll do from now on is reduce my temperatures where I can, and where I can't, I'll reduce the cooking time.

That sound like a good idea?

In reply to an earlier post on 26 Sep 2011 19:38:27 BDT
You have the right idea. But always test the food before eating, at least until you are happy with how the oven works for your recipes and food.

If you are in any doubt check the meat with an oven thermometer. I like to use this one.

In reply to an earlier post on 26 Sep 2011 22:22:48 BDT
M. Fisher says:
Ive been using fan ovens for years yes high temp foods reduce 20c eg 220 down to 200c lower temp reduce cooking time by 5-10 mins fan assist ovens reduce temp variations

Posted on 27 Sep 2011 09:52:29 BDT
baffy says:

Thanks everyone. I have a meat thermometer, but it's one where I have to take the meat out of the oven to use it, so I think I might treat myself and get the one suggested. You can never have enough kitchen gadgets, I think!


Posted on 27 Sep 2011 10:41:15 BDT
Richard says:
I have a fantastic Siemens oven with various settings including fan and conventional top and bottom heat (i.e. no fan). The instructions recommend cooking cakes and bread on the non-fan setting and this works fine. What is the advantage of this over the fan setting? I'm guessing it has something to do with heat radiating from the top instead of just having hot air blown past. The disadvantage is you can only use one shelf at a time as I discovered when I tried to bake two trays of bread rolls and forgot to change it to the fan setting - the top rolls were well fired on top and the bottom tray was barely cooked..

Posted on 27 Sep 2011 12:36:00 BDT
Last edited by the author on 27 Sep 2011 12:36:58 BDT
baffy says:
If you do a search on the web regarding cooking temperatures and fan ovens (as I've done a lot of recently), you'll find baking is one of the major issues that comes up.

From what I gather, it's common when baking in a fan oven for the outside to overcook while the inside is undercooked, and it would seem that is the efficiency of the fan oven that causes this. Reducing the temperature and/or cooking time would seem to be the way to go in this case - certainly in the case of bread, I would have thought that lowering the temperature would be a good thing to do. If you don't use the fan you will always have the top of the oven hotter than the bottom - this can sometimes be useful, but obviously not if you've got bread rolls on both shelves!

In reply to an earlier post on 27 Sep 2011 12:42:04 BDT
Last edited by the author on 27 Sep 2011 12:43:29 BDT
We've found that using the fan is less good for delicate baking such as small cup-cakes. However, if you need to cook a lot quickly, and you are not after ultimate perfection, then three shelves of CCs will still work OK with the fan mode.
But then my daughter, who is our cake expert, IS a perfectionist. And she still rues the loss of her commercial oven; up to three shelves of bread loaves nine to a shelf or four trays of French sticks, with the options of fans, top&bottom heat, top radiant, steam, motorised spit, etc.

Posted on 27 Sep 2011 14:05:39 BDT
Richard says:
For bread I prefer hot and quick as less hot and longer gives the loaf a tough crust.
I can see the logic as to why a fan oven may not be so good for cakes although lowering the temperature ought to allow for that - perhaps not with very large cakes.

Posted on 28 Sep 2011 11:28:15 BDT
S. D. Evans says:
I have a fan oven and tried all sorts to get bread (in particular) to cook properly. Eventually, I bought an oven thermometer and checked the actual temperature for each setting on the oven thermostat. The thermostat read anywhere from 10C to 20C low at different settings, so I made a list of the actual temperatures against the settings and stuck it on the inside of a nearby cupboard door. I can now accurately set the temperature at least.

Posted on 29 Sep 2011 11:40:17 BDT
Julian says:
when a conventional over is set to 200 degrees that is the temprature that it tries to the point where the thermostat top hotter bottom cooler...a fan oven should have same temp around all of long as you have left gaps between the trays and over sides...on all fours sides!

I tend to reduce temp by about 20 degrees and check food from 10 to 20% less time onwards...till its cooked how i want it :)

Posted on 29 Sep 2011 14:55:00 BDT
For my fan oven, I've found that where temperatures of 195C and above are called for, I reduce the temp by 20C and keep the cooking time the same. For 190C and below I usually reduce the temp by 10C and/or reduce the cooking time, depending on how long the food takes to cook.

Posted on 29 Apr 2013 18:06:27 BDT
Double S says:
I have had my fan oven for years and baked successfully in it. I recently had the element replaced and since then using tried and tested cake recipe I find that the top (not the middle) is not cooked although the rest of the cake is fine. I have checked with a thermometer and when the oven is set for 130C the actual temperature is 150C. As the recipe calls for 150C I have always set the oven at 130C and had no problems. Would love to know what is going wrong now.

In reply to an earlier post on 29 Apr 2013 21:20:54 BDT
Julian you,ve just hit the nail on the head. Everyone seems to be complicating the issue. I,ve had three different cookers over 30 years, I,ve got a Miele at the moment , but I had an AEG before that and I cannot e en remember the initial cooker. They all were the same, I,ve baked, roasted and stewed quite happily with the fan oven only, 20* lower temperature and checking after 3/4 of the cooking time, things often take less time when cake baking.

Posted on 29 Apr 2013 22:04:09 BDT
Spock says:

Posted on 30 Apr 2013 05:24:51 BDT
[Deleted by the author on 30 Apr 2013 05:26:27 BDT]

Posted on 30 Apr 2013 23:13:58 BDT
Spock says:
Hmm, deleted, but the mail hasn't appeared in my inbox. I have it tracked but.......

Posted on 5 Feb 2014 14:06:12 GMT
MarianM says:
I've been wondering why I haven't had a single cake success using the fan oven in my new range cooker, an exact replacement for my old one despite following the recommended temperatures for fan ovens in recipes. Using an oven thermometer I find that it's heating 20degs hotter or more than it should, as has my husband using his thermal probe (ooooh matron!) I'm trying to get hold of an oven engineer.

In reply to an earlier post on 5 Feb 2014 15:13:32 GMT
pixie says:
A fan oven wouldn't be my first choice Marian..I hear lots of complaints about temp. Hope it gets sorted.

Posted on 5 Feb 2014 15:49:14 GMT
MarianM says:
Thanks Pixie. Me too. My old fan oven was fantastic - baked fantastic cakes. This new one is obviously hot headed. While we're waiting for the engineer I must remember to lower the temperature knob by at least 20degs no matter what the recipe says for fan ovens.

In reply to an earlier post on 5 Feb 2014 15:54:38 GMT
pixie says:
I know thats the form for adjusting recipes...but fan oven recipes should be have a little baking gremlin...when he's been outed you'll be back to frustrating!

Posted on 5 Feb 2014 17:09:59 GMT
MarianM says:
Absolutely. Nasty little gremlin. When I set the oven to 180degs it really should be 180degs & not 200 or more. I really thought I was losing my touch as well as my marbles!
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Discussion in:  cooking discussion forum
Participants:  19
Total posts:  76
Initial post:  26 Sep 2011
Latest post:  12 Feb 2014

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