cooking-timeoven
In an oven, when following cooking times from a recipe, do I have to adjust times if I change quantity? I don't mean thicker or thinner food, I mean more or less of the same size, like e.g. more or less potato wedges.
Or does the thermostat in the oven just make the burner stay on for different times naturally and thus deliver the same amount of energy per mass of food over time (assuming I don't put too much food in at once).
The forced movement (convection) of the hot air by fans is what improves the cooking in a convection oven. The beautiful part is that it allows you to cook on ANY or EVERY single rack in your oven. Here are the adjustments you'll need to make:
For baked goods you typically drop the temperature by 25°F (10°C). If the recipe says to bake at 350°F then you'd bake at 325°F in a convection oven. This is most important in baked goods so that the interior has a chance to cook through before the exterior is overcooked or burnt.
You also need to decrease the baking time by 10-15 PERCENT. To make it easier to determine when to check, I usually suggest checking the item about 5-10 minutes earlier than the shorter time indicated in the recipe. If a recipe says bake 25-30 minutes, then check it at about 20 minutes. It may need a bit more time but you'll be pretty close.
When roasting meats and vegetables you can use the above method OR you can leave it at the regular temperature and then cook for 25-30 PERCENT less time.
In the instance of method #1 for meat you'll get less shrinkage and less chance of possibly drying it out.
In the instance of method #2 for meat, it will cook quicker and get better browning and therefore a bit more flavor.
A third option to take advantage of both methods is to cook it at the reduced temperature for most of the time but then turn it up 25-50°F for the last 20-30 minutes of cooking to improve the browning.
Presumably the reason you're cooking directly on the oven rack is to let the fat drip down. If so, do yourself a favour and get yourself a roasting rack. It's an inexpensive piece of equipment that you place in a baking pan or on a cookie sheet; the food cooks on the rack and the pan/sheet catches all the drippings. Way better than trying to replace an entire oven rack.
And if you really hate cleanup, you can line the pan with parchment paper or aluminum foil and just throw the rack in the dishwasher when you're done.
Best Answer
Many ovens do not have a thermostat. They have a timer, which turns the heating elements on and off in a predetermined pattern. As a result, the oven is a very imprecise heating instrument. It is frequently miscalibrated, and even for a calibrated oven, the temperature you set is the average temperature, while the actual temperature of the air inside varies in a roughly sinusoidal pattern, and the internal temperature of the baked good is even more irregular depending on its composition, location, choice of baking tin, oven type, etc. Even if the oven has a thermostat, it only (roughly) regulates the air temperature, not the internal temperature of the food.
As a result, the change in heating speed caused by adding a little bit more mass is really insignificant when compared to the huge variability of heating speed which is inherently present between ovens.
Luckily, many recipes are not very sensitive, and taste good no matter how much heat transfer actually happened during the time prescribed in the recipe. For these, you don't have to sweat it, keeping the original time is mostly OK. If you create major occlusion (e.g. two separate pans of gratin above each other), add some time by gut feeling, and check frequently for doneness toward the end.
For sensitive recipes (roasts, custards, some cakes), baking by time doesn't work anyway. The best you can expect from a time given in the recipe is a rough guide to help with planning when to start preparation for a meal. You have to always bake these until they are done, regardless of what the recipe says. In this case, you again don't have to do any time adjustments, because you are not baking by time.
To summarize, no, you don't really have to do any adjustments to time. Just bake everything until it is done, and if your time-based expectations were wrong, adjust based on doneness.