Does cooking more than one thing in the oven take longer?

Question

Ex: Cooking 2 pizzas (same temp/time needed) in the oven at the same time. Can I just set the same temperature and time as cooking one, and they’ll both come out perfect still? Why or why not? (Let’s ignore differences in cooking based on which rack the pizza is on lol)

I don’t cook much lol, so I’m trying to wrap my head around how cooking “consumes(?)” heat energy. More food mass isn’t going to *reduce* the temperature in the oven or anything… is it? And, the food masses aren’t connected, so not sharing heat distribution(?), so that seems like they shouldn’t affect each other?

In: Physics

Answer 1

> And, the food masses aren’t connected, so not sharing heat distribution(?), so that seems like they shouldn’t affect each other?

The oven heats the air, which heats the pizza.  So if pizza one absorbs a lot of heat from the air, pizza 2 will not be able to receive that heat from the air.

Or you can think about it in terms of energy. A Calorie (like what’s on food labels) is the energy required to heat 1 kilogram of water by 1 degree C.

So if you want to boil a kilogram of water in the oven from 20 C to 100 C, it takes 80 Calories of heat energy (not counting what’s wasted heating air and metal).

If you wanted to boil 2 kilograms of water, then it takes 160 Calories. Or if you keep the energy output fixed at 80 Calories, you’ll heat both kilograms of water to 60 C.

So yes, adding more stuff to the oven means it will cook slower IN THEORY.

In practice, the difference is usually negligible.

1. Tons of energy is wasted heating the air, oven insides, plus whatever leaks out. So going from 1 pizza to 2 pizzas takes maybe 10% more energy, not double.

2. The oven is temperature-controlled, not energy-controlled. So if you set the oven to 350 F, it will keep adding heat until that temperature is reached. Extra mass in the oven just means the initial heating is slower.

3. For most foods, the initial heat is a small portion of the overall cooking time. Like maybe it takes an extra 5 minutes to heat a lasagna that’s going to bake for 45 minutes.

TL;DR technically yes, putting more food in the oven would cook slower, but it usually matters less than which rack you’re cooking on. The effect would be more noticable if you cooked something for a short amount of time (like some pizzas) or if you had a smaller oven (like a toaster oven).