|I was watching Iron Chef America, and one of the
contestants used liquid nitrogen to prepare part
of their meal; how does liquid nitrogen work, and
is it safe for consumption?
|Question Date: 2010-06-04|
Liquid nitrogen is a very cold liquid. Its
boiling point is 77K, which is -196 C or -321 F.
So, when you see it in its liquid form, it is at
that temperature. It works by bringing things
that it touches down to that temperature, as it
consumes heat in order to boil. For an analogy:
Imagine if the world was normally really hot (150
C, or 302 F), and you had water sitting around.
It boils at 100 C, or 212 F, so it would pull heat
away from its surroundings in order to boil - A
pot in the stove is like this "hot world".
When you cook with liquid nitrogen, it freezes
any water that is in the food ingredients.
Typically, the nitrogen boils away and you don't
end up eating any. Since the atmosphere is 70%
nitrogen, we don't really notice it around us as a
gas either. If you were to consume liquid
nitrogen (as a liquid), it would cause severe
injury or death. It would cause freezing of the
tissue around your mouth or esophagus, which would
be severely painful and dangerous - therefore I do
not recommend eating liquid nitrogen! Great care
must be taken when cooking with liquid nitrogen to
make sure that things don't get too cold, as you
can cause internal or external frostbite. In the
lab, we always handle liquid nitrogen with safety
glasses, gloves, and long sleeves/pants and
closed-toe shoes, since we do not want topical
frostbite or blindness.
direct consumption of liquid nitrogen is not safe.
Consumption of foods prepared with liquid
nitrogen are safe, if it is not too cold.
Hope that is what you are looking for!
At room temperature nitrogen is a gas. In fact,
about 78% of the air we breathe is nitrogen gas.
However, at very low temperatures nitrogen
undergoes a phase change from gas to liquid. This
happens at 77 Kelvin, which is about -321 degree
Fahrenheit! This is so cold that is will freeze
just about anything instantly. This makes liquid
nitrogen great for making ice cream, but it also
means that you should always be very careful when
handling liquid nitrogen because it can give you
frostbite if a large amount of it comes in contact
with your skin. Liquid nitrogen is safe to use in
food because it immediately boils and just goes
into the air as harmless nitrogen gas, but you
have to be very careful with it while it is still
in liquid form.
Liquid nitrogen is just N2, the same
molecule that constitutes about 3/4of our
atmosphere, but in liquid form. The only
difference is it's much colder. It's temperature
is 77 degrees Kelvin, or 77 degrees above absolute
zero. To put that in perspective, room
temperature (around 70 or75 degrees F) is about
295 degrees Kelvin.
Another comparison to
make is to water. Water freezes at 273 degrees
Kelvin (32 degrees F) and boils at 383 degrees
Kelvin (212 degrees F). Although liquid nitrogen
is very cold, it is actually boiling! When it
boils it just becomes gaseous N2 and is
entirely safe to inhale. The only danger is the
low temperature can burn people if freezes their
Nitrogen comes from the air. About 79% of the
air we breathe in and out is nitrogen. Although
the important part of the air for us is oxygen,
the nitrogen doesn't do anything because it's
inert, so it just goes in and out of our
Liquid nitrogen is just nitrogen
from the air. The air is cooled down enough so
that it turns into liquid, then the nitrogen can
be separated from the other parts of the air. The
boiling point of nitrogen is -320 Fahrenheit
Degrees, so when it's a liquid, it's at or below
this temperature. You definitely shouldn't
consume liquid nitrogen, because it's so cold that
it could damage your body. But if it's just used
in preparation of the food, the food should be
safe to eat, as long as the food has been given
time to reach normal temperatures again. Whatever
liquid nitrogen remaining with the food, it will
have evaporated by then.
Nitrogen has a boiling temperature of 77
Kelvin, or -196 Celsius. Causing liquid nitrogen
to boil into gas takes energy, and that means that
it will cool off whatever it is in contact with
until it is at the boiling temperature or the
liquid entirely evaporates into gas. This means
that anything containing water (including most
food) will be very, very frozen.Liquid nitrogen is
dangerous only because it is cold. Once it
evaporates and becomes nitrogen gas, it's just
like any other nitrogen in the atmosphere, and
roughly 80% of the atmosphere is nitrogen gas.
Used in a closed space, this can still be
dangerous because it can lower the concentration
of oxygen. However, with proper ventilation (or
outside), nitrogen gas is harmless, and liquid
nitrogen becomes gas very quickly.
There is nothing especially magical about
liquid N2. At 1 bar pressure or the
typical pressure at the Earth's surface near sea
level, Nitrogen is a diatomic molecule
N2. It boils at one bar at 77 K.....
Thats 77 Kelvin or 77 degrees above absolute
The conversion from K to centigrade
is to subtract 273. So deg C= deg K -273. Hence
diatomic nitrogen boils (or liquefies from a gas,
its the same thing!) at a chilly -196 deg C. the
temp rite now in SB is about 20 deg C!!!
Recall that about 80% of the AIR we breathe is
diatomic nitrogen! Its quite inert chemically at
least at earth surface temperatures; it does not
react too readily in the gas state. When oxidized
we can get nitrates and nitrites. Nitrate is an
important food for plants.
nitrogen is safe as far as toxic effect, liquid
N2 is VERY COLD and if you handle it
improperly it can 'burn' you.
At any rate
the main use of liquid N2 in cooking is
to chill something very fast!
Here is what
some top chefs do
Thank you so much for your question.
Nitrogen gas composes about 77% of the air that
we breathe - liquid nitrogen is just the nitrogen
taken from the air under pressure to put it in its
liquid state. The boiling point of nitrogen is
-186 degrees Celsius, meaning that it is very,
very cold as a liquid and is boiling at room
temperature. Any steam that you see is a result
of the condensation of water from the air. Using
it in cooking is becoming more common to rapidly
cool/freeze items - one of my favorites is using
liquid nitrogen to make ice cream, and I know
there is a shop in the Denver, CO area known for
making their ice cream to order using liquid
N2. So in the aspect of using the
element nitrogen for cooking - it is safe for
consumption as it just boils away and makes the
food very cold.
However, there are always
some safety concerns. Due to the risk of
frostbite you should wear appropriate gloves for
handling liquid nitrogen, never stick your hands
into the liquid, and be careful of eating and
handling solid foods that have just become frozen
with it. Also, the Dewar (like a thermos for
containing liquid nitrogen) should be clean - so
as not to transfer any dust/dirt to the food.
Click Here to return to the search form.
Copyright © 2017 The Regents of the University of California,
All Rights Reserved.