Liquid Nitrogen Ice Cream
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
- 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!
- 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.
- 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
- 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:
- 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.
- 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
- Large bowl for making the ice
cream - 13 quart heavy stainless steel - required.
- 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.
- An extremely stiff whisk.
These can only be bought from commercial kitchen supply vendors.
- Paper towels - lots.
- 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
||per batch of
about 40-60 servings
liters - same amount as the volume of liquid used!
||Started with 5 + 40
liters. Threw away perhaps 20 liters
(Smart&Final) lightweight plastic spoons
200, not everyone used a spoon
Spoons tend to get spilled onto the ground, dropped, etc., so you need
cups (Smart&Final). 3 oz. paper cups work better (2005).
||300ea 3oz paper cups
||4 half gallons
||1 - 1 1/2 quart
(up to 2 qt)
||1 - 1 1/2 quart
(up to 2 qt)
Sugar. C&H sells this in 1/2 gallon milk carton sized (4 pound)
containers. Regular sugar works too, but does not dissolve as
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)
||1 oz (pour
Julia Child-like, several large blurps - do not measure)
pint-sized bottle chocolate sprinkles, lots of regular sized chips
||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.
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
- 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.
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
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.
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
- 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
- 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
- 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
- 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.
- Use shaved chocolate.
Perhaps chocolate powder (I have not tried this).
- 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
- 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.
- 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
- 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