I talk about the technique of varying the
pressure in a fryer to change how it cooks food. Lower temperatures and pressures allow the
food to be dried, and infused with oil without scorching or browning it. Higher
temperatures and pressures keep the interior of the food moist while darkening
the exterior. Fruits and vegetables are generally more appealing when vacuum
fried, and chicken is arguably better when pressure fried.
hey everyone I
wanted to talk about a
technique called vacuum frying today
so traditionally frying deep fat frying
is a technique where we put the food
into hot oil and remove some of the
water from the food at the same time
replacing a portion of it with the hot
oil and while this is all going on the
heat from the oil also cooks the food so
we have both a cooking and sort of
another alteration going on with the
food however if you ever wanted to fry
something like a fruit or a vegetable
the problem is that there's a lot of
water in that item and at a temperature
high enough to cause the water to boil
away the outside would become scorched
and the inside would still be too moist
so the vacuum frying technique allows us
to change the boiling point of water by
lowering the pressure in the pot just
like high-altitude cooking you have to
adjust the cooking time to compensate
for the atmosphere so here's three
batches of fried bananas that I just
made and this is the vacuum fried
bananas the bananas fried at normal
atmospheric pressure and then also
bananas fried under higher pressure so
with the same setup that I just built I
can also fry things under pressure and
that technique is actually used in
fast-food restaurants for fried chicken
and I'll talk about the reasons why in a
minute so the vacuum fried bananas are
fairly stiff they have a nice crispy
outside and if we cut one in half it's
actually fairly firm all throughout
although the inside is moist however the
normal fried bananas have a very very
thin skin on the outside and are
actually fairly soft throughout and the
pressure fried bananas are extremely
crisp on the outside but are also
surprisingly soft on the inside so the
vacuum fried bananas were cooked at a
lower temperature than the atmospheric
fried bananas and that was also still a
lower temperature than the pressure
fried bananas so you might be saying
well it's not surprising that this is
more cooked almost burned up here
because the temperature was higher
however that is the point of this whole
process the vacuum frying allows us to
do this oil water exchange at a lower
temperature so we don't actually have to
cook the fruit we can keep it
losing all of its flavor I mean it has
an uncooked flavor to it and we don't
have to brown it we don't have to cook
it like that so the vacuum of fried
bananas have a really nice crunch to
them this is by far my favorite out of
the three the normal fried bananas are a
little soft a little squishy and these
have a nice crispy outside but the taste
is kind of burnt I mean it does taste a
bit like charcoal so that's kind of too
much so here's how I did it I started
with a commercial stainless steel
pressure cooker that I bought at Bed
Bath & Beyond today I removed the
handle
from the lid and all the safety features
and noticed that it had two holes
already drilled for the pressure relief
valve in like the normal relief valve I
loosely screwed in a couple of eighth
inch brass pipe fittings and then silver
soldered them on the other side I
connected the chamber up to my vacuum
pump and pumped it down and then
realized I had a problem the seal that
comes with this pressure cooker is meant
to be inflated by the pressure so if you
try to pull a vacuum inside a pot like
this the seal actually pulls itself in
and it breaks the seal so I took a piece
of stainless steel welding rod and sort
of bent it into a circle and under
spring pressure basically put it inside
the seal so that would hold the seal out
to the outside and this actually worked
just fine for a while after a couple
runs there was enough oil kind of around
the lid area that the seal was still
slippery enough to pull itself in when
when vacuum was applied so if I were
going to keep using this setup I would
have to come up with a basic a stronger
ring maybe a continuous ring so that it
won't collapse in on itself I added a
cold trap to the system which is
basically a thermos filled with
denatured alcohol and dry ice and the
idea here is that all of the water that
we're going to pull out of those bananas
is going to end up in the cold trap
instead of in my vacuum pump so I talked
about how to make this in an earlier
video in fact in my astronaut ice cream
video and the amount of water is fairly
substantial so if all of that water went
into the vacuum pump it would you know
rust up and if it was enough water it
might actually lock the pump up
I'm using an induction cooktop which
I'll probably take apart in another
video to see how it works
it has a precision temperature control
on the front so that I can dial in the
temperature that I want the pot to be
and that's actually very close to the
temperature that the oil is in the pot
I'm kind of curious how it knows the
exact temperature it might be doing a
trick with the actual magnetics to
determine the temperature of the steel
however think it's also likely that
there's a temperature sensor just in the
base either IR or just contact for the
vacuum frying I got the oil up to about
110 degrees C and then loaded the banana
slices in the pot and put the lid on and
pull the vacuum as well as the vacuum
pump could manage so I think in the
literature there's sometimes specify a
very low pressure that's you know above
what a vacuum pump can make to there's
some regulation going on but in my case
I just did as much vacuum as the pump
could handle I cooked the bananas for
about 12 minutes and then opens the pot
up and took them out the atmosphere at
cooking was pretty standard I raised the
oil temperature to about 170 degrees C
and cooked them for a little under 10
minutes so I know I'm varying the
cooking time as well but the surface had
become so scorched that I realized that
it was was not going to be a desirable
thing if it really cooks that much for
the pressure cooking I changed one of
the fittings on the lid and then raised
the oil temperature to about 230 degrees
C and the idea with the temperature
changes is to match the vapor pressure
of the water in the food so with the
additional pressure in the chamber I
want the water to have just about the
same propensity to leave the food so
that temperature change corresponds to
the pressure change in theory this means
that the food would be equally dried
since the water has just as much for
reason to leave the food with these
different conditions however the higher
temperature means that more cooking
process will happen and that's exactly
what we can see here I used my
compressed air nozzle to add some
pressure to the chamber and tried to
keep it at just
over one atmosphere of course taking the
food out is more difficult with the
pressure case because as soon as we
lower the pressure all the food starts
boiling extremely vigorously because
it's been ramped up to this very high
temperature and has been sort of
stabilized at a higher temperature and
pressure this whole system is
potentially practical for home use I
don't think we really need the dry ice
for the cold trap since the pressures
are a bit higher I think we could get
away with a less good vacuum pump and a
less good cold trap and still get some
pretty good results okay see you next
time bye
s
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