Cooking is all about moving heat from one place to another. From the gas flame to the water, from the oven air to the turkey, from the hot soup on our spoon to the cool room air. Luckily there is a whole branch of physics dedicated to understanding how heat is transferred from one place to another.
In the kitchen we are generally interested in heat flowing from fluids (oven air or boiling water) to solid (meat or vegetables). Heat moves between fluids and solids following the equation below.
Q=h*A*ΔT
Q - rate of heat transfer (how quickly the heat is moving)
h - heat transfer coefficient of the fluid
A - area of contact
ΔT - the difference in temperature between the fluid and solid
This is a simple equation that provides us with some very useful information that we can apply in the kitchen. The rate of heat transfer is proportional to the heat transfer coefficient of the fluid, the area over which the fluid and solid are touching and the temperature difference between the fluid and the solid, increasing any of these will increase the rate of heat transfer which means our food will cook faster.
In the kitchen we are generally interested in heat flowing from fluids (oven air or boiling water) to solid (meat or vegetables). Heat moves between fluids and solids following the equation below.
Q=h*A*ΔT
Q - rate of heat transfer (how quickly the heat is moving)
h - heat transfer coefficient of the fluid
A - area of contact
ΔT - the difference in temperature between the fluid and solid
This is a simple equation that provides us with some very useful information that we can apply in the kitchen. The rate of heat transfer is proportional to the heat transfer coefficient of the fluid, the area over which the fluid and solid are touching and the temperature difference between the fluid and the solid, increasing any of these will increase the rate of heat transfer which means our food will cook faster.
Remove these ads by
Signing UpStep 1: Increase The Heat Transfer Coefficient
The heat transfer coefficient depends on a number of factors including the geometry of the solid. But all we care about is that it is proportional to the thermal conductivity of the fluid, which is property of the fluid that can be looked up in a table. Thermal conductivies vary widely for different materials. The thermal conductivities (k) of common cooking fluids are given below in W/mK.
Air 0.024
Alcohol 0.17
Olive Oil 0.17
Water 0.58
With a thermal conductivity of 0.58, water is 24 times better at conducting heat than air. You already know this, because you know that boiling potatoes is faster than baking them. And you know that you can go outside in the winter without gloves even if it's well below 0, but you wouldn't stick your hands in a bowl of ice water.
How can we use this knowledge to our advantage?
Cook faster
Water transfers heat much faster than air, while oil is somewhere in between. If you want to heat something up quickly you are much better off boiling or frying it than you are baking it. Similarly, if you need to cool something down quickly running it under cold water will cool it down much faster than blowing on it.
Cook better
Fast heat isn't always a good thing. Meat heated past 77°C is tough and dry so adding meat to boiling water will bring it up to 100°C quickly and give an unpleasant result. Meat is better cooked very quickly so that the internal temperature remains below 77°C when the outside is cooked or in an environment where the rate of heat transfer is slower.
Cook safer
If you need to thaw meat for dinner the natural thing to do is to leave it out on a warm counter. But air is a great insulator and thawing chicken this way can take hours. In the mean time parts of the chicken can warm to room temperature and allow harmful bacteria to grow. A safer, and faster, way to thaw chicken is to place it in ice water. Even though the ice water is colder than room temperature (23°C) it is warmer than your freezer (-15°C) and because water is such a great conductor it can do more with a 15 degree difference than air can do with a difference of almost 40 degrees.
Hack your Kitchen
Solids in general, but metals especially, are much better conductors that fluids. To defrost something in a real hurry put it on a large metal baking sheet or frying pan. Aluminum has a thermal conductivity of 250W/mK! Think of it as a reverse heat sink.
Air 0.024
Alcohol 0.17
Olive Oil 0.17
Water 0.58
With a thermal conductivity of 0.58, water is 24 times better at conducting heat than air. You already know this, because you know that boiling potatoes is faster than baking them. And you know that you can go outside in the winter without gloves even if it's well below 0, but you wouldn't stick your hands in a bowl of ice water.
How can we use this knowledge to our advantage?
Cook faster
Water transfers heat much faster than air, while oil is somewhere in between. If you want to heat something up quickly you are much better off boiling or frying it than you are baking it. Similarly, if you need to cool something down quickly running it under cold water will cool it down much faster than blowing on it.
Cook better
Fast heat isn't always a good thing. Meat heated past 77°C is tough and dry so adding meat to boiling water will bring it up to 100°C quickly and give an unpleasant result. Meat is better cooked very quickly so that the internal temperature remains below 77°C when the outside is cooked or in an environment where the rate of heat transfer is slower.
Cook safer
If you need to thaw meat for dinner the natural thing to do is to leave it out on a warm counter. But air is a great insulator and thawing chicken this way can take hours. In the mean time parts of the chicken can warm to room temperature and allow harmful bacteria to grow. A safer, and faster, way to thaw chicken is to place it in ice water. Even though the ice water is colder than room temperature (23°C) it is warmer than your freezer (-15°C) and because water is such a great conductor it can do more with a 15 degree difference than air can do with a difference of almost 40 degrees.
Hack your Kitchen
Solids in general, but metals especially, are much better conductors that fluids. To defrost something in a real hurry put it on a large metal baking sheet or frying pan. Aluminum has a thermal conductivity of 250W/mK! Think of it as a reverse heat sink.
Visit Our Store »
Go Pro Today »
Thank you for sharing!