Making astronaut ice cream in my home shop--- make money online

In his recent post, Chris Gammell used astronaut ice cream as a fun example of how high tech innovation trickles down to consumer-level products. Seeing an image of astronaut ice cream in my G+ feed got me thinking about

making some of my own. I managed to accomplish this with a harbor freight vacuum pump, some dry ice and various hoses and fittings. The process is known as freeze-drying and allows water to pass directly from ice to vapor, thus allowing the ice cream to maintain its physical structure while it is dried.

What should I freeze-dry next?

I have very fond memories of getting

astronaut ice cream when my parents

would take me to a museum when I was a

kid so I decided to try to recreate the

experience here in the home shop by

making my own astronaut ice cream so

let's see how it came out it's just like

how I remember it

let me show you how I did this astronaut

ice cream is just normal ice cream that

has been freeze-dried and so the process

of freeze drying allows us to remove

water without letting the water melt

first so in this case the water goes

straight from ice a solid to vapour and

by doing this the structure of the ice

cream is preserved so if you took some

ice cream out of the freezer and just

let it sit on the counter eventually it

would melt into a puddle and if you've

kept waiting eventually all the water

would evaporate away and you'd be left

with sort of a sludge so the sludge

doesn't resemble the original ice cream

because the structure is missing ice

cream has a lot of air whipped up into

it and so to preserve that porous area

it's necessary to get the water out

without letting it melt so lucky for us

water has a property that will allow us

to get the water out without letting it

melt and this is called sublimation so

by lowering the pressure on the piece of

ice cream we can get the water to go

straight from solid to gas so this is

how a freeze dryer is basically built we

have the chamber here and I'll get into

the exact temperature that we're going

to use where you put your food and then

this is called a cold trap so this is

just a section of lime that is held at a

lower temperature than the chamber so in

this case I was using dry ice and

ethanol just as a bath to transfer the

heat to the tube and this is at negative

70 C about for dry ice and then there's

a vacuum pump that will lower the

pressure in the whole system and allow

this to work so what happens is when the

vacuum pump is turned on the pressure is

lowered and the water will start to

sublimate out of the ice cream and

travel through the tube and actually get

stuck here and the reason it gets stuck

here is because it's much colder in the

cold trap and it isn't

chamber and for a given pressure the

water will sublimate here and then re

solidify here so we end up with with the

water being sucked out of the ice-cream

and transferred into this cold trap and

then when the process is over you can

empty the cold trap out which is going

to be filled with water or ice and the

product will be dry so I started with a

Harbor Freight three CFM vacuum pump CFM

is cubic feet per minute this is the

biggest one that they sell as far as I

know and I modified it by taking off the

fitting that was originally there for

air conditioning service this pump was

meant to evacuate the air conditioning

system in your car house and replaced it

with a much larger hose fitting the

reason for doing this is that at low

pressures the pressure is necessary to

sublimate water the flow through a

really thin hose is actually quite poor

it seems a little counterintuitive but

at really low pressure is it vacuums at

high vacuums the tubing actually needs

to be larger to allow those gas

molecules and water molecules to flow

through there the pressure is so low

that there isn't enough force to push

the fluid through the hose so it's

necessary to use a large diameter so the

next piece I built was this cold trap

which is a piece of copper pipe and some

standard pipe fittings that I just you

know cut and sweated together a standard

solder and they are sitting in a thermos

a stainless steel thermos that I filled

with ethanol and dry ice so this is a

good way it's a if you don't need liquid

nitrogen temperatures a dry ice ethanol

bath is a good alternative because it's

a lot cheaper and easier to maintain I

can get dry ice at Safeway which is what

I usually do they're open late at night

and you get dry ice any time of day or

night for the chamber I used a glass

Erlenmeyer flask and the reason I did

this was so that I could keep an eye on

the sample my first I actually had a

previous attempt at doing this I used a

stainless steel dehydration chamber or

sublimation chamber and the problem was

that I couldn't see what was going on

with the ice cream inside there so I

ended up putting in too much heat which

I'll get into later and the ice cream

melts

so that didn't work so I preferred to

have a glass chamber and I made a

specialized cork by boring it out with a

piece of copper pipe and then I sweated

on a flare fitting which I can use to

monitor the pressure so the trick is

that the the line going to the pressure

gage can be quite small in diameter

because it's not really flowing anything

the line from the cold trap to the

chamber must be again quite large to

make sure that enough water flows

through there even at these low

pressures the first step in this process

is to make sure that the ice cream is

really solidly frozen so I modified a

standard water cooler by a short Egret

by passing its temperature sensor so

that the compressor would run all the

time and then I filled it up with

denatured alcohol and measured the

temperature to see how cold it would get

and it would get down to about negative

25 Celsius which was just short of the

target I was shooting for about negative

30 or even negative 35 I read in in one

of the patents that any solution that

has sucrose in it would need to be

chilled below negative 30 degrees C for

a complicated reason that I barely

understand but basically sucrose

solutions even though the pressure is

low enough to sublimate water will still

have a structural change when you try to

sublimate the thing just because of the

high amount of sucrose in the solution

so anyway so I was shooting for like

negative 30 or negative 30 C so what I

did was I put the flask in the water

cooler after loading it up with some ice

cream this is a Neapolitan Klondike bar

and then added some dry ice to the to

the water cooler to get it down below

negative 30 so I left the flask in there

atmospheric pressure with the ice cream

in it at negative 30 for a little while

to make sure that the ice cream is

really that cold I also added a bunch of

dry ice to the thermos and had a little

bit of an overflow there good thing

there's no audio track on this one so

after getting the process started I

realized that I could raise the

temperature in the chamber without

melting the ice cream and the reason

that we can do this or apply heat to the

chain

without melting the ice cream the reason

we can do this is that by lowering the

pressure the water molecules are

transferring are converting from solid

to vapor and they're taking heat with

them so this is known as a sublimation

cooling you might have also heard of

evaporative cooling when the liquid

changes to a vapor so by pumping out all

the water we're actually simultaneously

cooling and drying the ice cream the

cooling effect is so large that we

actually have to put in a lot of heat in

order to make sure that the ice cream

will fully sublimate in a reasonable

amount of time so commercial freeze

drying machines have heated shelves in

them so you freeze the product first

lower the pressure and then heat them up

actually apply heat to it to make sure

to drive off the water and make it go

from solid to vapor

I took the flask out of the water cooler

and then used two tungsten light bulbs

to radiate some heat in there and I used

light bulbs instead of just submerging

it in a warm water bath because there

isn't a whole lot of conduction going on

between the ice cream and the flask wall

that's really necessary to have a

radiation a radiative heater to beam the

heat through the glass onto the ice

cream and commercial-free Striders have

like heating elements sort of like a

space heater to radiate heat towards the

food so I set this up last night before

going to bed and let it run overnight

and when I came in this morning there

was a huge chunk of ice the ice was even

visible sticking out of the cold trap

and the pressure gauge was reading high

like higher than it can measure so I

thought I had lost it but somehow

luckily this all worked out what had

happened was as the there was so much

water extracted from the ice cream that

the cold trap filled up it was plugged

so I took it all apart in MTB ice out of

the cold trap and then put it back

together and let it run for another

eight hours today so I had a total of

about 18 hours of pumping and I think

that's more than enough it probably was

done sooner than that but it's kind of

hard to tell I should add that the

chocolate was a problem the chocolate

doesn't freeze dry it stays

runni even even after all the water has

been removed it's probably because of

the high fat content so in the future if

I do this again I would either use ice

cream that has no chocolate on it or

just do a better job of cutting it off

of course I had to do Neapolitan because

you know the astronaut ice cream here's

a phase diagram for water and so

normally at atmospheric pressure which

is what I'm showing with this dotted

line here your ice cream starts off

solid it's cold and if you heat it up it

eventually reaches this point here where

it turns into a liquid and if you keep

heating it by boiling it on the stove it

eventually becomes a vapor and the water

will be gone and you'll be left with a

sludge basically all the components of

ice cream that aren't water but in this

case what we're doing here is starting

here again the ice cream is cold and

it's at atmospheric pressure and what we

do is we lower the pressure so moving

down on the chart to here then we start

raising the temperature so we go

straight from solid to vapor this by the

way is the critical point which I've

talked about a little bit in some of my

other videos where the difference

between liquid and vapor ceases to exist

so what you can do is transfer is go

from liquid to vapor by going around

this critical point and you never have

to transition through this line so phase

diagrams are pretty cool I encourage you

to look at these for other substances

and there's actually quite a bit more

detail that I haven't included here

which is pretty interesting okay well

I'm taking suggestions on what to

freeze-dry next so put that in the

comments and I will see you next time

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