Recipes: August 2009 Archives

Perfect popcorn, the physicist's way

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Tired of unpopped kernels and burnt popcorn? Sick of that yellow salty/greasy artificial "butter"? Upgrade your popcorn experience with these simple tricks and make perfect popcorn by understanding the basic physics behind it. You'll be rewarded by a healthy, whole grain and low calories delicious snack.

First, let's look at how a corn kernel pops:

Heat transforms the water content of the kernel into water vapor, and when the pressure is high enough, the kernel pops. That brings our attention on the two main parameters of our experience : water content of the kernels and heat transfer from the pan to the kernels.

Water content : soak it
If your corn kernels are a little old, chances are they do not pop properly. Soak them in water for 15 minutes, pat them really dry and pop them.

I tried this simple experiment : I popped 1/4 cup of kernels, then I popped 1/4 cup of soaked and pat-dried kernels. I ate the two popcorn bowls (joking -- I saved most of it for later) and counted the unpopped or half-popped kernels. The result? It's a tie : 10 for the dry kernels and 13 for the soaked kernels (the difference is not significant enough to draw a conclusion). My kernels are still really fresh, so I will have to retry this experiments with older and drier kernels to see if it really makes a difference (but according to Bill Nye the science guy, it does). So, if your kernels are still fresh skip the soaking step.  

Heat transfer : a little oil goes a long way
I learned this the hard way. I was tried to make a no-fat popcorn but it was a disaster. The kernels popped very unevenly, so by the time the last ones popped, the first ones were burnt. Also, they were smaller than usual, and often hard and half-popped. Disaster, I say.

Oil is essential to pop corn kernels on the stove top. Oil promotes an even heat transfer from the pan to the kernels. A heavy bottomed pan also helps for the same reason. I usually use 0.5 to 1 tablespoon of olive oil per 1/4 cup of kernels.

To successfully pop kernels on the stove top, heat the oil and the corn kernels on hi in a heavy bottomed pan with a lid on. Lift the pan, shake it and put it back on the stove top from time to time so that the kernels are heated evenly. Do that lift-and-shake maneuver more often when the kernels start to pop. When the pops are 2 seconds apart, remove the pan from heat and let it cool for a minute with the lid on. Transfer to a serving bowl and salt to your taste. Mmm...

popcorn.jpg Other tips
- Use very fine salt, such as the one you get from a salt mill. It sticks to the popcorn, as opposed to table salt which ends up at the bottom of the bowl.
- Olive oil is healthier than many other oils, but it doesn't withstand heat very well. Grape seed oil would do a better job here.
- Plain corn kernels are way cheaper than buying bags of microwavable popcorn. Buy organic ones if you can find them. They are 4$/kg at my local grocery store. Beat that, Orville Redenbacher! 
- 1/4 cup of kernels yield about 5-6 cups of popcorn.
- There are about 35 Cal per cup of popcorn, plus the calories from the oil (about 15 Cal per cup if you used 1 tbs of oil for popping), so it's about 50 Cal per cup of oil-popped popcorn.
- Pimp your popcorn with spices and herbs. I like mixes such as cumin-cayenne-allspice-cinnamon, or Italian herbs and grated Parmesan cheese. Be creative and share your favorite popcorn flavor in the comments below!

Making ice cream with liquid nitrogen is a delicious way to observe the phenomenon of phase transition, but the real reason physicists make ice cream that way is that it looks darn cool at a party. This is a discussion of my latest experiment with ice cream to clarify the process for people who might be interested in trying it.

1 - Get the liquid nitrogen. That's the toughest part. Liquid nitrogen (LN2) is cheaper than milk, but you can't buy it at the grocery store. We use it to cool down sensitive cameras for spectroscopic experiments in our lab, so we have an easy access to it at the university. It usually comes in big containers of 70 liters, so for the party we have to carry it in a smaller container. For the recipe, we will need 2 to 5 liters of LN2, which we can carry in special thermos-like bottles. Never, ever put liquid nitrogen in a closed container! The pressure will build up and the container will explode with LN2 flying everywhere (I know this by personal experience). The cap of our thermos bottle has a hole in it, so the pressure is regulated.

LN2_2.jpg 2 - Make the ice cream base. This is the recipe I used :
  • 1 liter of half and half (10% fat cream)
  • 0.5 liter of heavy cream (35% fat cream)
  • a pinch of salt
  • 1 cup of sugar
  • real vanilla extract, to taste (or other flavor)

Stir all the ingredients together until the sugar dissolves. I suggest you chill this mix in the fridge until you are ready to make the ice cream, unless you have plenty of LN2. Note that this recipe feeds 20 persons, feel free to halve it.

3 - It's time for the show. Pick an assistant and make her wear protective goggles and cryogenic gloves (or just mittens). While you slowly pour the LN2, your assistant has to stir constantly with a whisk or a wooden spoon. That's the key to make good ice cream : the ice crystals must be small for the ultimate fine-textured ice cream, so keep stirrin'! The mixture will boil, so be sure to use a big metal bowl to avoid spilling (some plastics might not resist those cold temperatures). When the mix is to thick to use a whisk, stir vigourously with a wooden spoon. Keep pouring slowly LN2 until it is the consistency you like.

LN2_4.jpgLN2_5.jpgLN2 boils at -196 degrees Celcius (77 Kelvin), and in order to change from a liquid to a gas, it has to absorb some energy (5.56 kJ per mole, to be exact). It thus takes this energy away from the cream, which cools it. By losing thermal energy, the cream will eventually turn into a solid, what we scientists call "ice cream". ;-)

4 - Taste test. Mmmm-mmmm! The recipe I used was totaly improvised and worked out beautifully. Try it!

Concerns about liquid nitrogen

Some people might have some questions and concerns about using LN2 for making food. For instance, Heidi from 101 cookbook (her blog is amazing, have a look at it!) details some of her questions on her post about the first time she made liquid nitrogen ice cream. Let's examine them.

  • "Will I die if I eat it (the ice cream)?"
No. Let the LN2 completely boil off (evaporate) and there is no danger for eating the ice cream.
  • Are those plumes of Halloween-looking smoke coming off the bowl going to gobble up all the oxygen in the room? Are we all going to go to sleep and never wake up?
No. The air we breathe is made of 79% nitrogen, so if you let a liter or two of liquid nitrogen evaporate in a room, it won't make much difference to what you normally breathe. But if someone spills a 4 foot high hardcore nitrogen tank in your kitchen, open the window.
By the way, the Halloween-looking "smoke" is nothing more than water vapor that condensates into small clouds. The same thing happens is you open your freezer on a hot and humid day, or when you exhale outside in winter at -30 degrees Celsius.
  • You need to treat it as seriously as you would a deep fryer filled with hot oil and the like.
Good point, you should be very careful when handling LN2.  But there is a big difference between hot oil and cold liquid nitrogen. If you spill hot oil on your bare hand, you will get burned real bad. If you spill liquid nitrogen on your bare hand, you won't get hurt. Why? The LN2 doesn't actually touches you : the droplets float on a small air cushion between itself and your hand. You can observe the same phenomenon if you spill a couple of drops of water in a very hot pan : the droplets float on a cushion of vapor. That being said, don't try to keep the LN2 in the palm of your hand, it will freeze your skin and that's not cool.

About this Archive

This page is a archive of entries in the Recipes category from August 2009.

Recipes: April 2009 is the previous archive.

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