The Science of Cooking Steaks
Let’s apply what we have learned about food chemistry, food safety, temperature, heat, and water to the cooking of a popular ingredient: steaks.
For the novice cook, one of the most confusing and frustrating experiences is deciding when a piece of steak is done. There is the palm method, where you touch different fingers with your thumb, and the hardness of your palm in different configurations matches different doneness. Or (according to some) an easier method: the softness of different parts of your face corresponding to the different degrees of doneness. I am not going to give you the details of these methods, because they don’t work: every person’s hand or face is different, every piece of steak is different, and do you really have a repeatable and accurate sense of touch?
Maybe you don’t care for steaks. But a rectangular piece of meat is a good subject to study how temperature and heat work in cooking.
The Problem Statement
First, let’s define what we mean by a steak well cooked.
The basic building blocks of animal meat are myofilaments (protein cells), which bundle together to form myofibrils. This bundling of bundles goes on until muscles are formed. Around each of these bundles is a sheath of collagen. As the temperature rises to around 60⁰C, the collagens begin to contract and squeeze the moisture out of muscle cells. To keep your ribeye juicy, you want to keep the internal temperature of the steak under 60⁰C (140⁰F). As it turns out, 60⁰C is about the lowest temperature at which beef is safe to eat.
Water in the meat fiber is not the only reason the meat tastes juicy. When you bite into a piece of meat, there is that initial burst of meat juice. As you continue to chew, the fat and flavor in meat stimulate the flow of our own saliva, which sustains the sensation of juiciness. A piece of bland, moist meat is not juicy. The distinctive flavors of seared steaks come from the Maillard reactions. Under high temperatures, the protein and sugar in the meat undergo a series of complicated reactions, producing hundreds of new molecules that result in intense flavors. These are called the Maillard reactions. They are some of the most important flavor-producing reactions in cooking. The Maillard reactions do happen at lower temperatures, but they accelerate at around 130⁰C. At that temperature, the water has evaporated. So the meat has to be dry where Maillard reactions happen. In other words, you want them to happen in part of your steak, but not too big a part.
To sum up, our problem statement becomes: we want a barely cooked interior and a browned crust. The ideal temperature distribution inside the steak looks like this:
It’s not a problem unique to cooking steaks. A lot of cooking is about getting to a desired temperature profile inside the ingredients. It gets more complicated if the internal temperature can not be easily measured or if different parts of the food behave differently under the same temperature.
The Analysis
Three fundamental physical facts about a piece of steak on a hot pan are:
- The steak will not heat itself from the inside. The heat has to come from outside.
- Heat transfers inside the steak by conduction. This speed of heat conduction is finite, and it’s a property of the steak itself.
- The Fourier law, which states in conduction the heat transfer rate (heat flux) is proportional to the temperature difference and the inverse of heat resistance.
According to Fourier law, we can increase heat flux either by reducing the heat resistance or increasing the temperature difference. To reduce heat resistance we can add oil, which is a good heat conductor. To increase the temperature difference, we should wait until the pan is really hot before we put the meat in it. Another benefit of a really hot pan is that the food will not stick to the pan, partly due to the Leidenfrost effect.
The violent sizzling sound you hear when you drop a piece of steak in a hot pan is the water on the surface of the steak getting vaporized. If you don’t hear anything, that means your pan is not hot enough. However, the sizzling sound should not last too long. Or it means there is too much water on the steak. All the evaporation of water takes a lot of energy away, which causes the pan temperature to drop. At that point you are not searing your steak, you are boiling your steak.
A common misconception is searing the meat locks in the juice. Last I checked nobody is making raincoats out of seared meat. Actually, meat juice and soluble proteins continue to leak out of the meat throughout the cooking process. When they run into the hot pan surface, the water is evaporated, and the protein coagulates and participates in the Maillard reactions. That’s why you don’t see any liquid. But you will see meat juice on the serving plate when the surface of the steak cools down on the plate.
Our goal is not to cook the steak as fast as possible though. Our goal is to get the desired temperature profile inside the steak. Assuming the meat starts at 30⁰C and the pan is at 200⁰C. A minute after the meat is put in the pan, the temperature profile inside the meat looks like the blue line in figure 2. All the water at the surface has evaporated and a thin layer of meat has dried out. The temperature drops as we go deeper into the meat. We then run into a boiling zone, where the water boils and the temperature stays at 100⁰C. After the boiling zone, the temperature continues to drop.
After a few more minutes. More of the steak is dried out and the Maillard reactions happen there. The boiling zone moves further inside the steak. Over time, the dried-out zone on the outside gets thicker and the boiling zone continues to move further inside. This is shown as the red curve in figure 2.
We want to make sure all the meat is cooked to above 60⁰C, but we want to limit the expansion of the high-temperature/dried-out region, to get to something like the brown curve in figure 2. In other words, we want to raise the tail of the red curve while making it less steep. This means we must have a smaller heat flux into the steak. Traditional recipes will ask you to move the steak into a slow oven and let it finish. If you are patient, you can set the oven temperature lower to ensure a smaller heat flux into the steak. How long should you leave it in the oven? Don’t trust any recipe, the oven thermostat, or your own experience. Stick a meat thermometer sideways into the steak and monitor the temperature.
There is a final twist: to achieve your target temperature, you must remove the steak from heat before the internal temperature hits 60⁰C. The reason is this: when the steak is in the oven, the hottest part is the surface. When the steak is removed from the oven, the heat on the surface can go in one of two directions: it can go inside the steak, or it can go out into the air. Turns out air is not a very good conductor of heat (that’s why the fluffy down comforter keeps you warm), so the residue heat from the surface of the steak will dissipate inwards and continue to cook the inside of the steak. You can easily confirm this by sticking a meat thermometer in your steak and seeing its internal temperature rise. In my kitchen in the summer, the temperate in the middle of the steak keeps rising after 15 minutes. Effectively, this is continued gentle cooking.
Unfortunately relying on the residue heat is neither reliable nor repeatable. How much the temperature rises is different for different pieces of steak in different kitchens. It depends on the humidity of your kitchen, the ambient temperature, and whether there is a draft in your kitchen, among other things.
The steak does not absorb the meat juice when it’s resting. It’s true that if you cut open a piece of hot meat, a lot of juice flows out. But if you wait until it cools down, no juice seems to be flowing when you cut the steak. The real reason is that liquid is more viscous at low temperatures. For instance, water’s viscosity at 80⁰C is about 1/3 of the viscosity at 20⁰C. At a lower temperature, gelatin from the meat also forms a gel that further impedes the movement of the juice. That’s why sauces always become thicker between the hot stove and the table.
I suppose if you carefully control the heat, the thickness of the meat, the fat content and water content of the meat, and the timing, you can skip both the low oven step and the resting step to get to a good temperature profile. That seems to be what some well-known steak houses do according to videos on Youtube.
The Solution
The ultimate result of cooking by heat is a temperature gradient inside the ingredients. Part of the cook’s job is to control the temperature profile by manipulating heat flow. Knowing that doesn’t make you a good cook (far from it), but it is the basic framework to think about temperature and heat in cooking, so you can begin to ask the right questions.
Sous vide is so popular with professional chefs because it’s a consistent way to precisely control the temperature of ingredients. We can cook the steak sous vide first, so the whole piece of meat is at exactly the right temperature. We can then sear the surface to get our desired crust and the flavor from Maillard reactions. The Modernist Cuisine’s steak recipe directs you to dip the steak in liquid nitrogen after it has been cooked Sous Vide and before you sear it. I will leave it as an exercise for you to figure out the benefit of the liquid nitrogen dipping step.
The analysis above points to another interesting possibility: what if you cook the steak straight out of the freezer? Now for the heat to propagate inside, not only will it run into the boiling zone plateau, but it will also run into a melting zone plateau. Water and ice act as natural insulators. You can take your time to sear the exterior, without worrying about overcooking the interior. When you are satisfied with the crust, you can then transfer the steak to a low oven. Turns out American Test Kitchen has a recipe that does exactly that.
By the way, how do the pros do it? Line cooks at famous steak houses certainly are not in the habit of touching your steak with their fingers before serving it. They cook so many steaks every day, and they have such consistent control of their meat and oven, that they have developed pretty good intuition of what’s happening inside a steak. In other words, they just know. Almost all problems with home cooks can be reduced to this: you simply don’t have enough experience to know what is happening and what will happen to the food.
Some frequently asked questions:
Let’s tackle some commonly asked questions about cooking steaks.
- Do I need to temper the steak to room temperature when I take it out of the fridge?
No. Suppose you have a piece of steak that weighs 340 grams(12 Oz). You start at 4⁰C and you want to cook it so that 10% is crust at 130⁰C and the other 90% reaches 60⁰C. Beef is about 75% water. So to dry out the crust 25.5 grams of water needs to be vaporized. The specific heat of beef is roughly 3.2J/g K. The specific heat capacity of water is 4.18 J/g K. The latent heat to boil water is 2259 J/g K.
Assume room temperature is 25⁰C. A typical gas burner delivers 15000 BTU per hour. With 20% efficiency, it delivers 175 Joules per second to the steak. Under these conditions, it takes about 12 minutes to cook a steak starting at 4⁰C, and about 10 minutes to cook a steak starting at 25⁰C. Only a difference of 2 minutes.
It’s because the energy needed to vaporize the water in the crust dominates the energy needed to bring the rest of the steak to temperature. Don’t waste time tempering the steak. Monitor the temperature of the internal of the steak while you brown the surface. If the interior of the steak is not cooked when you are happy with the browning, put the steak in a slow oven to finish cooking. You will save time and get better results.
2. How many times should I flip the steak?
Many people say you should leave the steak alone and flip it only once. Heston Blumentha’s method is to flip it every 15 seconds. I have tried it both ways. I don’t detect a difference.
But one trial in a home kitchen by an amateur cook is hardly a controlled scientific experiment. When experiments are inconclusive, we look to theoretical prediction for guidance.
Three types of boundary conditions are commonly studied in heat transfer theory: 1. Constant temperature at the boundary. 2. Constant heat flux at the boundary. 3. Convection surface as the boundary. We can assume our stove delivers constant heat output, so the bottom side of the steak that touches the hot pan is under the second boundary condition. The top side is exposed to air so it’s under the third boundary condition. The steak itself can be modeled as a plane wall. Simulation shows that by turning the steaks more often, you get a thinner crust. A bigger percentage of the steak in the middle stays at the ideal temperature. In other words, you get a more juice steak, along with all the wonderful flavor compounds generated by the Maillard reaction.
But that’s assuming you have the perfect timing. You can overcook and undercook the steak with either method if you are a couple of minutes off on either side of the ideal time. The real important lesson from the simulation is you should worry more about the internal temperature of the steak than how often you flip it.
By the way, as long as your pan is hot enough and you use enough oil, you shouldn’t have a problem with the steak sticking to the pan even if you flip it often.
3. Grill on fire or pan-seared?
Depends on the fuel. On a grill, the steak mostly receives heat in the form of infrared radiation. In a hot pan, the heat is conducted into the meat. Charcoal burns very hot. Since radiation heat is proportional to the fourth power of the surface temperature, charcoal grills deliver much more radiant heat than either a propane fire or a hot pan can. Therefore you get the best crust on a charcoal grill. As meat juice drops into the fire and gets burnt, many new flavor compounds are created and give your meat the special grill flavor. Make sure after you get the crust, move the steak to the part of the grill that’s not directly on top of the charcoal, and finish cooking the steak with gentle warm air.
4. The steak seems to turn grey by the sous vide process. Is it ruined?
No. It’s normal. Raw meat is red due to the protein myoglobin. It’s not the same protein that causes blood to be red: that’s hemoglobin. Red juice from raw meat is commonly mistaken for blood. In reality, the blood of animals has been drained at the slaughterhouse to decrease the risk of spoilage. (Turning live animals into meat is a carefully controlled process. Many things can go wrong. For instance, if cows are left in cold rain before being slaughtered, the meat quality will suffer).
As myoglobin is cooked to around 60⁰C, the protein denatures and gets oxidized. Its color turns brown. However, color is not a reliable indicator of the meat’s temperature. There are too many variables in the reaction between the pigment, other proteins, and trace elements of different forms of Nitrogen. Use a thermometer to be sure.
The brown color is not appetizing, and Maillard reactions did not happen at the sous vide temperature. That’s why all the recipes recommend you sear the meat after sous vide cooking.
Ideas for a better sauté pan
Everyone knows you have to wait for the pan to get hot before you put ingredients in it. Wolfgang puck said he doesn’t need a thermometer, he just puts his hand on top of the pan and he knows when it’s hot enough. Well, it’s easy for someone who had spent a lifetime cooking and paying attention. I don’t have the same amount of experience. I don’t always pay attention. And I am bad with feelings anyway. I use an infrared thermometer.
The pan itself can have a few thermocouples embedded in different locations and sends the temperature information over a wireless transmitter embedded in the handle. The transmitter can be powered by a few thermal-electrical modules embedded in the walls of the pan. The TEMs generate electricity by taking advantage of the Seebeck effect. This design keeps the pan wireless without embedding a battery in the pan, which may not be a good idea considering the pan is literally in the fire.
Imagine your pan can tell you it’s hot enough to start cooking. The pan will let you know when you add too much food and crowd the pan, causing the temperature to drop rapidly. The pan will also let you know when you leave the food in the pan for too long, most of the water has evaporated and the pan temperature starts to rise rapidly.
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