All of us who like to hang in the kitchen, faced the oven moods – especially around the big holidays, when we cook the festive lunch or dinner. Eventually we learn the peculiarities of our own cooker and we hate baking outside of home.
In order to succeed in the oven cooking discipline, it's good to know the principle they work on. Sir Benjamin Thompson, or Count Rumford, as he was more famous with that nickname, accidentally found the first oven. Cookers dehydrate.
Without going into extra details, let's begin with the fact that a large part of the food we eat is actually water. In the process of cooking (roasting or baking), the water evaporates. We all know that the water boils at 100℃. Therefore, after the temperature at the surface reaches 100℃, the water starts evaporating.
The separated steam comes out of the ventilation opening of the oven in the end, but meanwhile, evokes indescribable chaos and temperature changes. In fact, humidity is the defining factor during baking. Unfortunately, as much as we adjust the temperature of the oven, we have no control over the aforementioned variable.
Of course, there's a window of time, that we have a full control. That's the moment, in which the oven is preheated, but the food is still not inside. You would say "What's the use?". The preheating of the oven is something really important, because it acts as an reservoir – an energy reserve. Oven roasting and baking depend on the air temperature. The heating coils heat the surrounding air, which in turn heats the food. Every time we open the oven door, the hot air flies to the kitchen ceiling. Every time we put a dish to bake, the temperature drops. The preheating allows for the oven walls to accumulate enough energy and in this way to lower the effect of the temperature amplitudes.
The time for preheating of the oven always seems painfully long. That is due to the fact that the bigger part of the hot air vanishes. In reality, the energy need to heat approximately 0.14 m3 of air up to 250℃, you need around 42 Kj. The heating element of a standard oven produces this amount of energy for the ridiculous 21 seconds. But, in order to heat the cooker walls, which is actually the aim of the preheating, you first need to get the air hot. And, as we know well, the air is a good insulator. Moreover, during heating it expands (because it's a gas) and the larger part of it floats through the ventilation opening.
When we take a piece of meat, let's say, beef steaks, and we decide to roast them in the oven at home, we count on the fact, that the oven, preheated to, let's say, 250℃ , will cook meat at that exact temperature. Is that really so? The answer is no. otherwise it would all be so simple!
Let's start from the very beginning. We take a piece of a steak, which we will roast, and we place it in a preheated oven. The hot air quickly leaves the battlefield, at the moment, we open the oven door. That automatically lowers the temperature inside. But that's not where the problems end. After the food is in the oven, there's another object in the system with a whole different temperature and it needs to heat. The temperature drops even further. In this case, the preheated oven walls help for the air temperature to rise quickly enough.
During roasting, two kinds of temperatures play the main roles. The temperature of the dry air, which the heating coils heat and the temperature of the moist air. The latter turns out to be the one at which the food actually cooks. What does it mean?
During the first roasting phase, the hot air in the oven interacts mainly with the moist surface of the food. The temperature in this zone rises, the meat slowly begins to evaporate water. The higher the temperature of the dry air, the more the evaporating. Crust begins to form on the surface. Due to the fact, that a certain amount of energy is needed for the water on the food surface to evaporate, this process actually cools down the meal. That slows down the rising of the rest of the food temperature. In fact, at this stage, the meat we roast is raw and cold in the middle, whereas hot and cooked at the surface. During the whole roasting time, the two temperatures fight for dominance, but in fact, the moist air temperature wins.
Directly under the surface, you can find the zone in which the water boils – the reason it evaporates later. It's relatively small. Until the water there evaporates completely, it doesn't matter what's the temperature you set. In this zone, the temperature will remain at 100℃, until the water completely evaporates. Therefore, the centre is still very cold.
The last zone – in the middle of the steak – is the diffusion one. There the water doesn't reach even 100℃. In this zone, the meat cooks thanks to the process called diffusion.
That zone is the largest. That's obvious because of the meat colour itself. Of course, the larger the meat chunk, the bigger the diffusion zone. That automatically means longer cooking time, so that the centre reaches the desired temperature.
What happens when we cook more often than not is that the food splatters and leftovers in the oven chamber clutter. With time, they will affect the temperature amplitudes in a negative way, meaning, your cooker will take longer to heat. A good piece of advice from many professional cleaners is to scrub the insides of your oven more regularly. Usually, the proper timing should be at least twice per year for a really good deep clean and periodic smaller ones every two months or so. That way, you will ensure that the food deposits won't act as an insulation barrier to temperature.