Fifty Minute Classroom

May 24, 2019, 11:15

50-Minute Classroom: Science Your Students Need to Know

01 March 2014

For starters, temperature and heat are not the same thing. When is convection mechanical, and when is it natural? And is food cooked by radiation harmful? Chef Weiner explains why all culinary students should understand the basic science behind critical processes in the kitchen.

By Adam Weiner, CFSE

Last month I raised the debate about teaching cooking science to students. My personal opinion is that there are a few science principles students need to know:

1. The only way to lose weight is to consume fewer calories than you burn. I realize that this is not technically cooking science. However, more and more pressure is being foisted upon the foodservice industry to help solve the obesity crisis. Students must be taught that sooner or later, they, their families and the customers of where they work must pay the piper when it comes to calories—and that this is a matter of personal responsibility.

2. Not understanding food science could make you sick. Students need to understand how bacteria grow, what is cross-contamination, etc. In a future article, I will write on how to teach food safety in 50 minutes. Yes, you can do it. I know, I do it for every starting class.

3. Heat and temperature are NOT the same thing. Heat is the energy of moving molecules. Temperature is how fast the molecules move. Have I lost you? Let’s look at it this way: A cup of boiling water is 212°F. A 40-gallon stockpot of boiling water is 212 degrees. The temperature is the same, but the heat of the stockpot is much greater. We know the heat is greater because a cup of boiling water placed in a freezer will freeze to a solid block fairly quickly, while the 40-gallon stockpot of boiling water (because it has more heat) will take considerably longer to freeze solid.

Furthermore, temperature could be high, and the heat could be low. You know you can stick your hand in a 350-degree oven (if you don’t touch anything in the oven) for a long time and still be comfortable, but you wouldn’t dare think of putting your hand in a 350-degree fryer. The reason is that the air molecules in the oven aren’t moving all that fast and there aren’t that many of them, while there are many more molecules in the oil (oil is denser than air) and they are moving faster.

A quiz question: Which has a higher temperature, the pilot light on your stove or a burner on full blast? The answer: They both are the same temperature, but the full-blast burner has more heat.

4. Much of cooking involves radiation! I ask my students if they would eat a hot dog cooked with radiation. They all say “no way!” Then I serve them hot dogs that I had cooked in the microwave and in the oven. They devour them. I then tell them that the hot dogs they ate were cooked with radiation. Many dry-heat techniques (such as grilling, roasting, broiling, baking, etc.) involve radiation of one form or another. Radiation means transfer of energy by waves. Convectional heat source, infrared ovens and microwaves all use radiation. Not all radiation involves nuclear radiation.

5. Cooking with conduction is different than cooking with convection. Convection cooking happens when heat is moved around the food. Convection can be by air, steam or liquid. Convection cooks food faster using a lower temperature, thus saving time and energy. (For convection ovens the electricity to power the fan is far less costly than the electricity or gas needed to heat the oven to a higher temperature for a longer time.)

My students often have a hard time grasping how the movement of air or steam makes things cook faster. To explain, I give them the following example: Suppose you are standing in the desert in the summer and there is no wind. It is 110 degrees and you feel hot, but it is bearable. Now, suppose a heavy wind comes through and hot air is hitting you in the face and all over your body, blowing along hot sand, as well. The temperature hasn’t changed, but you are feeling hotter and the hot sand is searing your skin. This is the opposite of wind chill; wind chill with driving snow or rain causes you to cool off faster. The movement of air (which involves the movement of molecules—in my example snow, rain, sand) conducts the energy of heat more effectively then non-moving air.

There are two types of convection: mechanical and natural. Mechanical convection occurs in steamers, convection ovens and enclosed rotisseries. As we all know, a convection oven has a fan in the oven circulating the air, and enclosed rotissuers and moving shelves in ovens do the same thing. Natural convection occurs because heat rises and coolness sinks. Many people find it difficult to give an example of natural convection. The best example I know of is watching a pot of stock or soup. You will see a piece of onion rise to the top in the middle of the pot and move to the outside where the pot is cooler, and then the onion sinks down. No one moved the onion and there was no fan involved. This is natural convection.

Conduction is when heat travels directly to the food being cooked. There is direct contact between the source of the heat and the food. This usually happens in two ways: 1) a pan, pot, plate, etc., is heated and the food is put on the pan, pot, plate, etc. Sautéing is a prime example. 2) Heat moves from one part of the food to another part of the food. For example, in a microwave the water molecules inside the food heat up from the inside and they heat the rest of the food. Another example is a large roast in an oven where the heat from the outside of the roast moves to the inside. Frequently both methods are involved, such as in grilling.

I have learned many things in my 10 years of teaching. One of them is that if you talk too long on one subject, particularly if it is an intense subject, you will lose your audience. So, there are a few more points of science that I think your students need to learn, and I will write about those next month.

Chef Adam Weiner, CFSE, teaches a 20-week Introduction to Cooking program for JobTrain on the San Francisco Peninsula.