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Culinary Thermal Management
As I continue this series on the science in cooking, I will discuss one of the methods of using liquid nitrogen (LN2) as it pertains to the culinary arts. I briefly touched on it in last weeks general overview of molecular gastronomy. While not a completely new idea, we have started seeing it’s use on a more regular basis. Even though it is not a kitchen staple now, I can see it becoming more popular as home cooks look for new ways to emulate their favorite chefs. The obvious attraction to using liquid nitrogen is the wow factor. Who wouldn’t like to transform their simple mixing bowl into a bubbling witches cauldron to create the ultimate ice cream? On the skeptical side, isn’t liquid nitrogen poisionious? The truth is that beyond the novelty aspect of it, there are some benefits to using it, as I will discuss further.
Even though liquid nitrogen used in cooking has been mentioned for quite some time, it has only become more popular in the last few years, as the culinary arts have seen a rise in popularity, mostly due to shows on cable television. With so many new chefs and television shows trying to create the “next best trend” in cooking, the use of science has become a key component. As I stated before, there are a few benefits to using liquid nitrogen. One of the best-known uses for liquid nitrogen is its ability to create ice cream with the smoothest, creamiest texture, in an instant. Adding in liquid nitrogen, as you mix your favorite ice cream base, causes the fat and water particles in the cream to freeze so quickly that they stay extremely small, creating the creamy texture. In your standard home ice cream maker, the mixture is turned as it slowly freezes allowing for larger crystals to form along with the incorporation of air. Another ice cream technique is to drop the ice cream mixture into a bowl of liquid nitrogen, through a baster, while continually stirring the nitrogen. This causes the ice cream to freeze into little balls, similar to the spherification technique. As a result you create something very similar to the carnival favorite Dipin’ Dots®. Liquid nitrogen is also used when creating extravagant cocktails. Adding a tiny amount to liquid not only cools the drink but intensifies the fogging cloud effect around the glass as well.
A Look at Liquid Gas
Now we will explore the more cautious and frightful side of using liquid nitrogen. To do this we need to understand what liquid nitrogen is and how it is used in other applications. Liquid nitrogen is the liquefied form of the element nitrogen and is commercially produced by fractional distillation of liquid air. This is the process by which components in a chemical mixture are separated according to their different boiling points. Vapors from a boiling solution are passed along a column. The temperature of the column gradually decreases along its length. Components with a higher boiling point condense on the column and return to the solution; components with a lower boiling point pass through the column and are collected.
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Gasoline produced from crude oil is another example of fractional distillation.
Under normal pressures, liquid nitrogen has a temperature between -346oF and -320.44oF. At this temperature, instantaneous frostbite can occur if the liquid nitrogen was to come in contact with living tissue. So how can we possibly think that it is ok to cook or serve drinks that contain liquid nitrogen? This is due to its low boiling point of -321oF at atmospheric pressure. As liquid nitrogen is released from its container, it begins to boil off and return to gas form. This is the smokey, fog like effect that you see when it is poured from its container, or used in cocktails. By the time that a drink or food prepared with liquid nitrogen is consumed, it has already converted back to a non-toxic, odorless and relatively inert gas and therefore does not pose a health risk when used in small amounts. Some of the commercial uses for liquid nitrogen include:
- Cryopreservation of biological samples
- Freezing and transportation of food products
- Coolant for superconductors and other materials and equipment
While there are inherent dangers involved with using liquid nitrogen, it is not any more harmful than cooking with boiling water or hot oil when standard safety precautions are used. Always handle liquid nitrogen with insulated gloves and eye protection. Also know that when liquid nitrogen is returned to its gas form, it displaces the oxygen around it, which is why it should only be used in small amounts in a well-ventilated area.
Next week, as I move forward on the topic of molecular gastronomy techniques, I will further discuss the technique I mentioned above: Spherification.
[i] http://chemistry.about.com/od/chemistryglossary/a/deffractdistill.htm
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