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Do I need to adjust the oven temperature in a roast duck recipe if I want to put more than one duck in the oven at a time.

I suspect I should keep the same temperature but keep them in longer. Should I cover each duck in foil individually or together? Does it matter if they are on the same pan?

rsavchenko
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Let's do some physics again:

All culinary aspects aside, a roast is a (more or less) solid "blob" with a certain mass and volume.

To get the roast to the desired doneness, you want to reach a certain temperature at the center of the meat. The crucial properties are the thermal conductivity and thermal diffusivity of your meat or, very simply put, how fast your meat transports the oven heat towards the center of your roast, which again is calculated on oven heat and starting temperature of your meat.

This depends on geometry, or, the maximum thickness of your meat. Hence the rule to stick your meat thermometer in the thickest part of your meat.

Two ducks next to each other are two separate masses, which heat up independently, not one roast of greater thickness:
Two ducks in your oven need basically the same time as one duck of the same size.
(A good oven should be capable of heating enough that the second duck won't lower the temperature significantly.)

Now to the practical points:

For the reasons discussed above, it is easiest if you choose two ducks of about the same size and weight. If not, one will need less time than the other and you might have to take one bird out of the oven sooner. If both shall be done at the same time, the smaller one needs to go in a short while after the bigger one - how much time difference is very hard to say, even with those handy "roasting time by weight" charts in cookbooks or on the Internet: Use a thermometer, not a timer, to determine doneness. (And don't forget that the core temperature will rise a few degrees even after you have taken the bird out.)

You ask about positioning in a conventional oven:
By all means roast your birds side by side, not one above the other. Stacked, they will be very close to the top or bottom heating element, which will at least dry them out but more likely burn the top or bottom, while shielding the other bird from the heat on one side. Even if you switch positions occasionally (do you really want to juggle hot pans?), you get the same effect of a "burned-but-undercooked" bird. And no, foil will not prevent this.

And just because we repeat it again and again:
Do not determine the doneness of your roast by a watch, use a meat thermometer.

Stephie
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    This is a great answer. Since we're "doing physics," I would just note that while *in theory* the time should be the same, *in practice* the time may vary *a bit* depending on how well the oven regulates temperature, whether two roasting pans side-by-side disrupt air flow significantly, and even more subtle matters like the amount of steam given off by food if the oven tends to be reasonably well-sealed. Generally these factors won't make a huge difference unless the oven is crowded. But I agree with your conclusion: just use a thermometer. – Athanasius Nov 24 '15 at 21:34
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    I hate to use processed food as a reference, why oh why would a bag of chicken nuggets or tatter tots instruct you to bake for 22-25 minutes if using half a bag, but lengthen that time to 25-28 minutes if using the whole bag? It's because their is more thermal mass dragging the heat of the oven down. @Athanasius is 100% correct about using the thermometer. – Escoce Nov 24 '15 at 23:46
  • @Escoce But as your ducks will need more than 25 minutes, the oven - which has a fluctuating temperature anyway - will be able to heat up enough during the roasting time, making the effect minimal. Your own comment states a difference of *three* minutes... different oven and refrigerator models (or starting with room-temperature birds) have a much greater effect. (Which leads us back to our trusty thermometer again.) – Stephie Nov 25 '15 at 04:37
  • The difference of three minutes is because tator tots and chicken wings are much smaller, less thermal mass. I am not saying the difference is going to be drastic mind you, just that there will be a measurable difference. – Escoce Nov 25 '15 at 16:04
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I suspect I should keep the same temperature but keep them in longer.

No.

The time it takes depends on the thickness of the largest piece of meat, not the total mass of meat. This is unlike the microwave oven, where the time does depend on the total mass, not just the thickness, because the microwave energy is a fixed unregulated amount and so more mass needs more energy.

It is important that the ducks have the same size and reside on the same height.

If you use the foil to prevent drying out, you should wrap each duck individually, as the point of the foil is to prevent moisture escaping, which is best done by eliminating any unnecessary air.

John Hammond
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  • I have found that using foil helps some dishes not dry out. Maybe duck fatty enough to where that shouldn't matter. – rsavchenko Nov 24 '15 at 19:57
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    I know it's just a digression but your claim about microwaves isn't really true. They do penetrate a bit, but they still heat mostly from the outside in, so there is still dependence on shape/thickness, not just total mass. – Cascabel Nov 24 '15 at 20:30