There are lots of different ways that we can cook food, or at least, a few different ways that we apply heat to food (after all, cooking is really just the application of heat to food). The science behind what happens when you put a chicken in an oven compared to what happens when you put a steak in a pan is a bit different. The end result is broadly the same, heat energy is transferred from the energy source to the food and the food is transformed (cooked), but how the energy is transferred, and the rate at which it happens differs.
Likewise, different things happen when you put food in an oven compared to putting it in hot liquid. The two techniques share more in common than compared to a pan, as the former are both take advantage of convection where as the pan relies on conduction for energy transfer. If like me you remember secondary school lessons about radiators and convection currents, you will know that convection is the movement of heat in a circular motion through gas or liquid. Bullet smokers (like the Weber Smokey Mountain) take advantage of convection currents, as do Kamados (and, aptly named convection ovens) to cook food.
When something is cooked by convection, heat energy is circulated around the food and as the gas/liquid particles that are charged with heat energy pass by the food the energy is transferred to the it (cooking it). The cooler particles descend back down to the heat source where they once again get heated up and continue the flow of the current.
1. Braising - cooking in liquid
Before we get into humidity, lets have a quick look at the science of braising and cooking food in a liquid.
As mentioned, braising or cooking in liquid, makes use of convection. The liquid is heated up and a convection current forms around the pan and as the hot liquid moves it passes over the food and transfers heat energy, the exact same way hot air does in an oven. However, despite sharing the same basic method of energy transfer, they cook quite differently. As you most likely know (although maybe haven’t thought on for too long, because why would you?), braising is a far more efficient means of cooking. If you cook short ribs in an oven at 120C, it might take you 8+ hours for them to be cooked nicely, where as if you put them in a casserole dish with braising liquid you could be looking at less than 3 hours cooking. But it’s not just the timing that is reduced in braising - the boiling point of water being 100C, if you braised them in water then they are guaranteed not to being heat to a temperature greater than 100C - so braising is a lower temperature and shorter time than the oven.
This is because cooking is about energy transfer, not about temperature. Oven roasting use the same energy transfer method but liquid can just hold a lot more energy than air can, even at a lower temperature. The simplest way to demostrate this is think about a time you have opened a 200C oven, maybe even reached your arm inside - that hot air that comes out is close to 200C, and the internal temperature of the oven is close to that (although dropping pretty quickly with the door open), and you can likely withstand that without too much discomfort. Compare this to a time you have got it a hot bath, or put your hand in very hot water - water at a temperature of just 60C will cause almost immediate third-degree burns to your skin. The air from a 200C oven is bearable, but 60C liquid is potentially resulting in a trip to A&E. The difference is quite stark.
The capacity for different substances (and their states of matter) to hold and retain heat energy is widely applicable in cooking - from cast iron skillets to the ceramics in kamado bbqs. And really, this is the salient point to think about when we think about liquid or even humidity (which is just the measure of the amount of liquid in the air).
2. Humidity levels and impact on cooking
Braising, or cooking sous vide, are both essentially 100% humidity - e.g. the environment the food is in is 100% liquid. In a convection oven, the humidity level will be a lot lower, down towards low single digits in most cases (in a BBQ with a water pan you might get to 10-15% humidity at the max).
As we know that it’s the ability of liquid to transfer energy that makes the difference in cooking, you can imagine the sliding scale of cooking efficiency from 100% humidity (braising/sous vide) down towards closer to 0 humidity of oven roasting. As we move down that scale, the transfer of energy becomes less efficient, so will take longer to cook.
For most intents and purposes though, does this make any difference to us? in reality, are we ever cooking in an environment other than the two ends of the spectrum? Quite possibly not, but that’s not to say we can’t benefit from this knowledge!
3. Hacking cooks with Humidity
The first way we can take advantage of this knowledge is something we probably all already do - The Texas Crutch a.k.a wrapping meat during cooking.
If you tightly wrap meat in foil during cooking, it creates an incredibly humid environment, as no moisture can escape the wrap and the meat gives off liquid during cooking. This will more efficiently cook your food and can speed up your cooking if running behind. It’s a technique commonly used to combat the stall in BBQing, but can accelerate cooking at any point. It’s also common to add additional liquid to the foil when wrapping the meat which just adds even more moisture to kickstart the humidity of the sealed environment (a technique I have since heard named Smoke-Float-Wrap by BrewshackBBQ).
Likewise, if you are running behind cooking a tough, hardworking piece of meat such as beef short rib, cheek etc, and you aren’t too worried about how it gets done, you can switch it out to a casserole dish with a little braising liquid (wine, stock, milk, water etc) and it will also accelerate cooking time (and create a great serving sauce).
Obviously, the wrap and the braise alter the end result of your cook as it introduces moisture to the meat, which may or may not be desirable. Another way to get around a slow moving cook is to quickly add it to a ziploc bag and cook it sous vide. Sous vide is 100% humidity but the food is protected from the actual liquid penetrating the meat by the plastic bag.
4. Disadvantages of a humid cook
It’s not all energy savings though - there are other considerations when trying to maximise humidity. For one, we are adding a lot more moisture to the food. If we are after a nice crisp bark on the surface of our meat, then humidity is not our friend, as it will keep the surface more moist. Further more, added moisture can get in the way of all sorts of delicious reactions that we are after when we cook - such as charring and the Maillard Effect.
If you have ever eaten these, cast your mind back to occasions when you have eaten steamed broccoli and when you have eaten oven roast broccoli. To my taste at least, one of them is wayyyyy superior in taste and texture!