Liquid Nitrogen Ice Cream

Liquid nitrogen ice cream has become somewhat of a hit at the SLAC Family Day, SLAC Take our Daughters(/children) to Work Day, and the Stanford Founder's Day. 

The purpose of this page is to document the ingredients, supplies, and methods.

All of the basic supplies are kept together - either in my office or in Public Affairs.  Missing are the consumables and the dewars.

Special note:  The use of any cryogen carries with it considerable risks, and should only be done by those familiar with the safe use of Liquid Nitrogen.  While is seems paradoxical to work with this material near young children, there are some important safety steps built into the procedures.  Items of particular note are:

  1. The dewar used in making ice cream is usually filled from a larger tank of nitrogen using a phase separator.  This uses nitrogen at high flow rates and thus with high risks - use face shields, proper gloves, and keep the youngsters away for this step!
  2. If you allow people to "touch" the nitrogen, make sure that nobody is permitted to keep their fingers in the liquid for more than about a second.
  3. Make sure that no children get in the immediate area of where the nitrogen is being poured into the bowl.  If you have an assistant, children may want to be between the two of you - and this is a problem.  Solve it, and get on with the exercise.
  4. No decanting of nitrogen into plastic soda bottles - these will explode it the top is screwed onto them.  If you do this with water bottles (which explode faster), you may have as few as 5 seconds between the cap being tightened and the explosion - so throw it out of the way fast.  I am not encouraging this activity, especially not with children under the age of 18 around.


The following tools are needed:

  1. Dewar for the nitrogen.  I like the 3 - 5 liter size dewars.  Important: this should be an "open top" dewar, and not a pressurized dewar.
  2. More nitrogen for the next batch.  This can be from a pressurized dewar.  If working at SLAC, the vacuum technicians can usually supply a 200 liter dewar with a phase separator with a days notice.  Be sure to ask for the "phase separator" - which is a pipe with a bronze filter that attaches to the liquid-phase valve.
  3. Large bowl for making the ice cream - 13 quart heavy stainless steel - required. 
  4. Extra bowl for science talk.  This can be smaller (8-10 qt) and works better if it is not as heavyweight as the mixing bowl.
  5. An extremely stiff whisk.  These can only be bought from commercial kitchen supply vendors.
  6. Paper towels - lots.
  7. Trash can for the uses ice cream cups, paper towels, etc.


The following were used in the April 2004 Founder's Day at Stanford - 6 or 7 batches (about 400 servings) were made, and at Take Our Children to Work Day 2004 - 5 batches were made (about 250 children plus adults).  Nitrogen consumption at Children day was less because there was almost no science talk about liquid air.

Item Founders 2004 Children 2004 Children 2005 per batch of about 40-60 servings
Nitrogen 25 liters 12 liters - same amount as the volume of liquid used! Started with 5 + 40 liters.  Threw away perhaps 20 liters 2 liter.  See note below.
Really cheap (Smart&Final) lightweight plastic spoons 500 About 200, not everyone used a spoon 250 75.  Spoons tend to get spilled onto the ground, dropped, etc., so you need too many.
3-4 oz soufflé cups (Smart&Final).  3 oz. paper cups work better (2005). 400 About 200 300ea 3oz paper cups 60.
Heavy cream (manufactures' cream) 2 gallons 1.75 gallons 4 half gallons 1 - 1 1/2 quart (up to 2 qt)
Whole Milk 2 gallons almost 1.25 gallons 2 gallons 1 - 1 1/2 quart (up to 2 qt)
Baker's (ultrafine) Sugar.  C&H sells this in 1/2 gallon milk carton sized (4 pound) containers.  Regular sugar works too, but does not dissolve as fast. 7 lb 3 lb few pounds.  Used only 1 overflowing serving cup per batch of 1/2-3/4 gallon.  More might have been better. 8 oz (two completely full serving cups)
Vanilla 6 oz 6 oz 16 oz 1 oz (pour Julia Child-like, several large blurps - do not measure)
Chocolate chips 4 bags - small 1 pint-sized bottle chocolate sprinkles, lots of regular sized chips (20 oz?) 2 pint-sized chocolate sprinkles (2+ lbs) 1/2 to 1 bag

The smallest batch is made with 1 quart half-and-half, 1 (of a bit less) cup sugar, 3 oz vanilla, and a handful of chips.  A small amount (1-2 liters) of nitrogen is needed.  This is the right amount for a Friday noontime BBQ with the summer students (8-10 people).  Use the 5 oz soufflé cups for adults.  Group BBQs for the NLC use 1/2 gallon cream, 1/2 gallon milk, and the rest is pretty clear.

Half-and-half can be substituted for the cream and milk.  For big batches, the cream available from Smart and Final in 1/2 gallon bottles and milk in gallon bottles is easier to use.  DO NOT accidentally buy non-fat half-and-half - the results are too sweet.

Actually, the nitrogen use is about equal to the volume of the liquids.  At Founder's day, we started with a warm 25 liter dewar plus a 5 liter dewar, both warm before we filled them up, and ended up with about 5 liters at the end of the day (6 hours later) - but each batch was made with a 1 1/2 to 2 liter sized dewar, so It seems that the amount needed depends to a large part how it is being stored.  Children's day, the nitrogen use was exactly the same as the liquid use.


  • Pour an inch of nitrogen into the spare bowl.
  • Ask what this is. Ask adults to be quiet if needed.  Talk about nitrogen.  Its in the air - that sort of stuff.
  • If it is not too windy, hold bowl at face height.  Notice liquid dripping off the bottom.  Liquid Oxygen - talk about why and this too.
  • Walk around with the bowl and let kids stick fingers into the liquid.  They will note that it is dry.  Make sure that nobody leaves their fingers in it (no macho allowed here).  Note:  SLAC ESH has disallowed this step for Take Our Children to Work Day 2004.
  • Dump nitrogen on ground in a spraying motion away from kids - never leave the liquid out alone!
  • Make the ice cream.  Ask them what you need, they probably already know.  Pour into the bowl:
    • 1 - 1 1/2 qt cream
    • 1 - 1 1/2 qt milk.  Reuse a empty cream container to measure the milk quantity if needed.
    • 2 measures sugar - use the soufflé cup to measure, and overflow it t times.
    • Blurp Vanilla (a few oz?)
  • Mix until sugar is dissolved.
  • Add Nitrogen - mix. 
    • Show off results - it is all bubbly.
    • A fog rises off the surface of the cream and across the table. 
    • Be prepared - Simultaneously, every child will cram towards the ice cream (this cannot be avoided).
    • Some will blow at the fog - this should be discouraged for food safety reasons.
  • More nitrogen - mix, etc. 
    • Do not be surprised if nitrogen droplets dance across the table on the 2nd or 3rd batch of nitrogen (I do not know why this happens). 
    • The smell of Vanilla is almost overpowering.
  • Be careful to rotate the bowl and mix the edges - as they freeze faster.  Stop and mix frozen milk/cream back into mix as needed.
  • Last - add chocolate.  Well, almost last.  You may need one more batch of nitrogen if the mix is too soft.
  • Stop now - tell everyone that:
    • There are enough spoons for everybody - no rush.  (put spoons into the first bowl and onto table)
    • There is enough ice cream too.
    • Ask that when you give the ice cream out, that they step back to give others a chance
  • Serve the ice cream.  What works really well is to gram a cup, scoop some (not too much) ice cream out, and give it to a waiting kid.  I try to make the arrogant ones wait a bit, and pass the ice cream to parents with really small children.  Parents and seconds are always last.
  • Wipe everything down with paper towels.


  1. You can use frozen yogurt mix (a bit hard to get) - some brands work better than others - I think the fat-free is the type that comes out too hard.  The chocolate mixes are really hard to clean up following (but taste good).
  2. You can make real ice cream from your favorite cookbook and bring to work cold (but unfrozen).  Batches as small as 1 qt can be made.  This tastes better, but I do not want to do it this way when I am serving the public.
  3. Use shaved chocolate.  Perhaps chocolate powder (I have not tried this).
  4. On how leisurely days (summer student BBQs, for example), take a second bowl and fill it part way with nitrogen.  Rest the ice cream bowl onto it (sort of like a double-boiler), and the cold boiloff will keel the ice cream frozen longer.
  5. Flowers can be frozen and stepped on, but watch out or else the kids will defoliate the garden area.  This can get out of hand really fast.
  6. Watch out for those plastic water bottles.  If filled and capped, the nitrogen boils until the bottle pops.  Since the pressure gets up to several hundreds of PSI, and will be quite dangerous to anyone in the area - within 10-20 feet (and unbelievably loud).  Make sure that this science experiment does NOT HAPPEN.
  7. At Stanford with the fountain with a smooth water face, pour a bit of nitrogen on the water.  The droplets do not move as fast on the water as on the ground - quite impressive!