How to make liquid nitrogen

Ice cream preparation with liquid nitrogen

Have you ever prepared two different types of ice cream for 60 people? Maybe yes, but within 15-20 minutes in front of an assembled audience that is completely fascinated and learns something in the process? With courage and liquid nitrogen, that's no problem ...

To the recipes: chocolate (30 people), vanilla (30 people) and - brand new - strawberry (10 people)

Liquid nitrogen is used as a refrigerant with a high heat capacity and is used, among other things. in science, food technology, medicine and the pharmaceutical industry, e.g. for shock freezing and freeze-drying of sensitive foods, cells, tissue, blood, biochemicals, etc., for gas storage of fruit and vegetables, in technology for cold grinding of otherwise tough elastic materials such as plastics and rubber Etc.

It is usually kept in insulated open vessels at its boiling temperature. At normal pressure it is -195.8 ° C, "ice cold" is much too warm a description for that.

Liquid nitrogen can of course be purchased from its manufacturers (e.g. L'Air Liquide). Often, however, the required quantities can be obtained in the physical or chemical departments of the university cities, in research institutions. A request from the nearest chemical company could also help.

Safety instructions:

Liquid nitrogen is fascinating, but it can also be dangerous. Therefore, it is essential to observe some precautionary rules:

  • Wear protective goggles that also cover the sides of the eyes.
  • The working document should be dry.
  • Avoid contact with skin, eyes and mucous membranes (risk of severe burns from cold)
  • Wear thick leather gloves and closed clothing and footwear (it is extremely painful if liquid nitrogen runs into the sandals or neckline)
  • Transport only in suitable containers, these must not be tightly closed (risk of explosion due to overpressure)
  • All devices that come into contact with liquid nitrogen become so cold that skin immediately freezes to them. Therefore, only handle these devices with leather gloves.
  • When transporting the jug in the car, clamp it so that it cannot tip over or slip. In addition, only drive with the window open. If nitrogen leaks, leave the car immediately and ensure good ventilation (nitrogen is non-toxic, but suffocating)
  • Never pour the remaining nitrogen down the drain, as the water in the siphon would freeze. What happens then should be clear.
  • Never, but really , use the cheaper liquid air (30% liquid O2, 70% liquid N2) or even liquid oxygen (100% O2) as a substitute for liquid nitrogen. Nitrogen preferentially evaporates from liquid air, thereby enriching the oxygen. Since oxygen is the carrier of every combustion, the first contact of organic matter (i.e. cream + milk) with the highly concentrated oxygen would lead to a huge explosion even at -182 ° C (boiling point of oxygen).

You also need

  • a large metal container that can hold at least three to four times the amount of the liquid used (do not use glass, porcelain or plastic: risk of breakage from cold shock).
  • a large whisk, wooden spoon and / or potato masher
  • a transport jug for liquid nitrogen (can sometimes be borrowed or rented from the supplier; do not use normal thermos flasks, as these are too poorly insulated and too small)

Ingredients:

for 3 liters of chocolate ice cream liquid you need:

  • 1 liter of whole milk 3.2%
  • 2 liters of whipped cream 32%
  • 350 g cocoa drink powder
  • 3 pack of vanilla sugar
  • 2 pack "Dr. Oetker dessert sauces without cooking" chocolate type
  • 900 g chocolate sprinkles or pieces, preferably dark chocolate.
  • 4-5 liters of liquid nitrogen

for 3 liters of raw vanilla ice cream you need:

  • 1 liter of whole milk 3.2%
  • 2 liters of whipped cream 32%
  • 6 pack sauce powder vanilla flavor from "Ruf"
  • 2 packs of bourbon vanilla sugar from Dr. Oetker
  • 250 grams of sugar
  • 4-5 liters of liquid nitrogen

Using more cream and less milk is good for the taste and bad for the figure.

preparation (should be done calmly before "the show"):
Chocolate / Vanilla: Put ½ liter of milk in a saucepan and heat until almost boiling. With the exception of the chocolate, dissolve all non-liquid ingredients in it while stirring.
Strawberry: see below

Now the show can begin:

Put the prepared liquid in a large tall saucepan and add the remaining liquid. The preparation bowl can be rinsed out with the rest of the milk. Finally, the chocolate chips are added.

While stirring vigorously, you pour a large shot of nitrogen into the liquid, but don't be scared: it hisses, it splatters and a bright white, completely opaque mist rises from the pot and immediately sinks over the table to the floor. Nevertheless, stirring and tamping must be continued quickly so that the boiling nitrogen foams the liquid. If the pot was too small, a lot of vanilla, chocolate or strawberry sauce runs onto the living room carpet ... Soon the mist begins to become transparent and as soon as you can see the liquid, nitrogen is added again.

When the first larger frozen lumps appear, the nitrogen is added a little more slowly so that the ice becomes evenly cold. I've got used to working with a potato masher; With it, the liquid, which is frozen hard on the surface, can be easily pressed in and mixed in. When the desired ice cream consistency is reached, it can be served.

How much liquid nitrogen is ultimately required depends primarily on the speed with which it is added and stirred. Precise information is therefore difficult, it is best to plan two to three times the volume of the raw mass.

If little nitrogen is added frequently, a lot of the show effect is lost, but it also saves refrigerant. So when things get tight, just add the nitrogen in sips and still work quickly, because "time is nitrogen".

It is also interesting to explain liquid nitrogen to the audience before preparing the ice cream. To do this, a little nitrogen is filled into a simple glass (try out beforehand whether it can withstand the cold shock!). One can mention the low temperature, but who can imagine -200 ° C! After a short while, the glass is frozen and the nitrogen stops boiling and splashing. If you now dip a flower (roses are very decorative) into the glass, this leads to brief foaming. If you take the rose out of the nitrogen, it looks completely normal. Only a little white mist flows down from it and immediately white frost forms. But don't let that distract you (if you do, just freeze it again in nitrogen), but immediately place the flower on the table or a board and hit it with a hammer. It will shatter into a thousand pieces as if it were made of glass. All soft materials such as strawberries, plums or even a piece of garden hose and empty balloons behave in a similar way.

It is also effective to first cool a banana deeply and then use it to hammer a nail into a board.

Inflated balloons collapse as the air inside them also becomes liquid.


My favorite

for approx. 2 kg strawberry ice cream (10 large servings) you need:
  • 1 kg of fresh aromatic strawberries
  • 6 cups of liquid whipped cream á 200 g
  • 50-150 g of sugar
  • Strawberry sauce and vanilla sugar to taste
  • a potato masher

Preparation: Wash, clean and sugar the strawberries. Let the sausages stand for a while (e.g. while grilling the starter) in the metal pot so that they can draw juice.

The show:
First pour one or two cups of cream over the strawberries and carefully mash the latter with the potato masher. This should not result in a homogeneous strawberry mud, but rather small pieces. Then mix in the rest of the cream. Season with the strawberry sauce depending on the aroma, color and taste of the mixture (we needed about 200 ml for the last mixture).

As usual, nitrogen is added in batches. Press the mass that has hardened on the surface down again and again with the potato masher and mix in. Serve immediately when the desired consistency is reached.



Literature:

© 1997-2008 Thomas Blenkers