February 12, 2025 • 11 mins
If you lived in ancient Persia, you could do a lot worse in trying to cool things down than by building a yakhchāl. Today we break down how the early fridges worked.
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Episode Transcript
Available transcripts are automatically generated. Complete accuracy is not guaranteed.
Speaker 1 (00:04):
Hey, and welcome to the Short Stuff. I'm Josh, and
there's Chuck Jerry sitting here free Dave, and so this
is short stuff. How do you say this again?
Speaker 2 (00:12):
Edition, Yeah, I'm gonna say it's pronounces spelled y ak
h you know, as most words are h A L.
I'm gonna say yakuls.
Speaker 1 (00:25):
I'm going with the straight ahead yakh chaws. All right, Okay,
so you say your way throughout. I'll say it my way,
and I'm sure all inevitably unconsciously start saying it your way.
Speaker 2 (00:37):
We'll see. But what we're talking about is the promise
from our refrigeration episode. A little bit more on these
ancient basically ancient refrigerators or cooling systems. They were found
across ancient Persia at least as old as four hundred BC.
This is modern day Iran, and this is these are
places where, I believe it or not, the climate enables
(01:01):
freezing of ice when you would not think you should
be able to freeze ice.
Speaker 1 (01:07):
Yeah, it's pretty amazing and apparently still today in Iran,
Afghanistan and to Jikistan, to jeek Stan. Yeah, I said
it right. The first time they called the refrigerators yak Chile's,
which is how I would say it if I were
in Iran. But that's the name for the fridge, which
means that at some point someone in Iran has gone
into a store and said, you got a smeg yak chaw?
Speaker 2 (01:31):
Yeah, exactly. And these have been the fascination of like
everyone from engineers to historians to physicists over the years
because they're just so kind of confusing and how they
actually work. And I'm still not entirely sure how it works.
It seems to be a little magic involved. One thing
(01:53):
I know goes a long way toward keeping this ice.
And we got to say some of this ice is
mined from the mountains, brought down and preserved. Some is
made on site. We'll get to that, but one big
factor is the insulation of the structure itself, which is
made from a mortar called serrouge.
Speaker 1 (02:14):
Was that how you're saying it?
Speaker 2 (02:15):
Sand, clay, egg whites, lime, goat, hair and ash quite
a mixture.
Speaker 1 (02:23):
Some of these were several meters thick. Some of these
yak chaws were. There was a study. We got some
of this information from the engineering for Max Fordham and
they did an analysis from twenty eighteen of yak Child's
and just how effective they might have been. And they
found that the walls of a yak chaw had the
same insulative properties as a wall of concrete three inches
(02:47):
thick surrounded by a one foot thick wrapping of styrofoam insulation.
That's how effective these things were.
Speaker 2 (02:55):
Sand, clay, egg whites, lime, and goat hair and ash.
Speaker 1 (02:59):
I was gonna say, like the secret egg whites, but
who knows you throw goat hair in there, and yeah,
who knows what the secret? I think the secret is
the whole thing together, the whole say rouge mysture?
Speaker 2 (03:13):
Yeah, probably so so I mentioned that sometimes the ice
was brought in from the mountains and kept there throughout
the year. But usually what would happen is is they
would make ice, They would bring in water. They would
divert water from an aqueduct through these underground water channels
called cannots, and they would channel them to the north
(03:35):
side of this wall. It's another thing we haven't mentioned
yet is they have these very very high walls that
act as shade for these channels to keep you know,
the wind off of it, because stuff isn't going to
freeze as fast if it's moving, so to keep the
water still and to keep it cooler away from that sun.
Speaker 1 (03:56):
Yeah, And so the channel has a little diversion into
a trench or a pit or like a very shallow
like rectangular pond usually, and it they'll divert water in
there to fill it up, and then they let it
freeze overnight. Over the course of a few nights, it'll
continue to freeze and freeze and freeze in layers. And
(04:18):
the what they're taking advantage of, you know, like when
it snows and then the temperatures heat up and all
the snow melts, but there's a little pile of snow
like in a shaded corner of your yard that never
gets direct sunlight. Yeah, and it just takes forever to melt.
There can be advantage of the same thing. They're building
that big old that big old wall to keep it
shaded and to just let this ice grow and grow
(04:41):
and grow. And then once it reaches I think fifty centimeters,
which is like about a half a meter thick, then
they'll cut it into blocks and they put it in
the yac shell and they store it through summer. Like
this stuff will stay frozen for an entire summer. So
in in that sense, these yak chails are built to
(05:02):
store cold throughout the course of a year, even when
the summer comes around still cold.
Speaker 2 (05:09):
Yeah. Another way that helps us out is that dome shape.
It's not domed because they like domes, even though domes
are nice. It's conical because that optimizes what's called the
solar chimney effect. Is that's when you create a convection current,
letting that heat go up, up, up and out through
these openings at the top and bringing in that cool
air from the bottom.
Speaker 1 (05:29):
They also have wind catchers that they call bad geers,
and they actually take win and direct it downward into
the yakchaw dome. And so the air that hits it
is cooled by that ice, and the air that's not
cool by it, or cooled enough, like you said, that
chimney effect takes it up along the curve sides toward
(05:49):
the hole in the top, and it says, see you later,
don't come back.
Speaker 2 (05:53):
That's right, And that feels like a good time for
a break, and we'll come back and talk about what
the heck they're doing with all this ice. This all right,
(06:27):
So they're making ice, they're preserving ice. What are they
doing with all this ice? One of the things they're
doing is using it as a refrigerator. You know, they'll
store food in there that they don't want to go bad,
and just using it as a as a cold house.
They will also just use the ice to eat in
a treat. They have something called Feluda over there, to
(06:51):
Persian traditional dessert has thin vermicelli noodles made from cornstarch,
and then you mix that up with a little semi
frozen sirr of sugar and rose water, and then serve
it up with a little lime juice and maybe some
ground pistachios. And it's like a little Persian icy.
Speaker 1 (07:09):
That has to be better than it sounds, don't you think?
Speaker 2 (07:11):
Oh I think it sounds great.
Speaker 1 (07:13):
I think the pistachos are where of throwing me off.
Speaker 2 (07:16):
Oh yeah, you don't like pistashios.
Speaker 1 (07:18):
Or I do like pisachos. It just they don't seem
to go with the rest of the ingreen eent. But
like I said, I'm sure it's delicious. I mean, it's
a traditional Persian dessert. It's got staying power. So yeah,
who am I to question for luda exactly?
Speaker 2 (07:32):
I bet it's delicious.
Speaker 1 (07:34):
One of the cool things about this is that yak
charles I mean, and there's some still around. I think
there's one in Kerman, Iran that's about the size of
a five story building. So you would think, of course,
obviously this was reserve for royalty. You would be dead wrong,
because not only were yakchels open and available to the public,
(07:56):
there are some that people just built for their houses
that were a private use of as well.
Speaker 2 (08:00):
Yeah, for sure, they would make those delicious falluda. They
would make surbets and preserve them and then nuts, fruit
and ice and they would put them on a donkey
and go sell them at market and stuff like that.
They would sell ice directly from those places sometimes. And
you know, one of the things they're also taking advantage
(08:22):
of is the greenhouse effect. You know, the earth is
going to stay fairly warm at night because of the
greenhouse effect trapping those gases in the atmosphere. But if
it's low humidity and if it's a really clear night,
that effect is going to be weaker and that heat
can dissipate and disappear more readily. And so that's when
they discovered, like, hey, we can make these little thin
(08:44):
layers of ice and kind of build, you know, day
by day, night by night on these clear, low humidity nights,
eventually to get you know, some pretty significant ice.
Speaker 1 (08:53):
And once they figure that out, someone said, go get
the donkey. Exactly, it's time to sell some Subert and
harvesome goat hair. One other thing I saw in that
Max Fordham analysis, they figured out that they could make
about what would be equivalent to three million ice cubes
a season.
Speaker 2 (09:12):
Wow.
Speaker 1 (09:13):
Yeah, which is a lot. But they were like, you'd
think it'd be more, and I was like, it seems
pretty good to me, especially in four hundred BC.
Speaker 2 (09:20):
You know, it depends on how big those cubes were.
Were they big fancy cocktail cubes. That's a lot more
ice than a ice nugget.
Speaker 1 (09:27):
That's right, You're absolutely right. I expect that they're probably
all donkey head size. So three million donkey head size
ice cubes, that's big. Think about the poor donkey that
had to cart those around. I know, no fun, you
got anything else?
Speaker 2 (09:43):
Yeah, I mean these went away obviously because of modern
refrigeration came on the scene. And also one thing that
was happening was they were making this ice kind of
out in the open, and a lot of it would
get contaminated with dust and it wasn't like the healthiest
ice in the world. And so that combined with modern
refrigeration coming along, they're like, maybe we should just not
(10:04):
have these much anymore. But like you mentioned, there is
one still around, at least in Kerman, and there are
groups there that are trying to preserve this way of
life and at least keep it, you know, not like
a chief refrigerating method, but like, hey, we can't lose
our culture, and so let's work to take some of
these old ones and restore them at least, even if
(10:25):
only for like museum and touring purposes.
Speaker 1 (10:28):
For sure, but also there's a lot to learn from them,
especially when we're trying to advance like passive cooling and
other things that require less energy to cool things down.
Yak Chaal's are something to turn to and say how
do we do this? And someone says, go get the
goat here.
Speaker 2 (10:44):
That's right, we'll get some egg whites too. No one
likes this.
Speaker 1 (10:48):
What do we do with all these yokes? Yeah, well,
I think that's it for short stuff, right, Chuck?
Speaker 2 (10:54):
I think so?
Speaker 1 (10:55):
Well? I mean short stuff is that.
Speaker 2 (11:00):
Stuff you Should Know is a production of iHeartRadio. For
more podcasts my iHeartRadio, visit the iHeartRadio app, Apple Podcasts,
or wherever you listen to your favorite shows.
Hey, and welcome to the Short Stuff. I'm Josh, and
there's Chuck Jerry sitting here free Dave, and so this
is short stuff. How do you say this again?
Speaker 2 (00:12):
Edition, Yeah, I'm gonna say it's pronounces spelled y ak
h you know, as most words are h A L.
I'm gonna say yakuls.
Speaker 1 (00:25):
I'm going with the straight ahead yakh chaws. All right, Okay,
so you say your way throughout. I'll say it my way,
and I'm sure all inevitably unconsciously start saying it your way.
Speaker 2 (00:37):
We'll see. But what we're talking about is the promise
from our refrigeration episode. A little bit more on these
ancient basically ancient refrigerators or cooling systems. They were found
across ancient Persia at least as old as four hundred BC.
This is modern day Iran, and this is these are
places where, I believe it or not, the climate enables
(01:01):
freezing of ice when you would not think you should
be able to freeze ice.
Speaker 1 (01:07):
Yeah, it's pretty amazing and apparently still today in Iran,
Afghanistan and to Jikistan, to jeek Stan. Yeah, I said
it right. The first time they called the refrigerators yak Chile's,
which is how I would say it if I were
in Iran. But that's the name for the fridge, which
means that at some point someone in Iran has gone
into a store and said, you got a smeg yak chaw?
Speaker 2 (01:31):
Yeah, exactly. And these have been the fascination of like
everyone from engineers to historians to physicists over the years
because they're just so kind of confusing and how they
actually work. And I'm still not entirely sure how it works.
It seems to be a little magic involved. One thing
(01:53):
I know goes a long way toward keeping this ice.
And we got to say some of this ice is
mined from the mountains, brought down and preserved. Some is
made on site. We'll get to that, but one big
factor is the insulation of the structure itself, which is
made from a mortar called serrouge.
Speaker 1 (02:14):
Was that how you're saying it?
Speaker 2 (02:15):
Sand, clay, egg whites, lime, goat, hair and ash quite
a mixture.
Speaker 1 (02:23):
Some of these were several meters thick. Some of these
yak chaws were. There was a study. We got some
of this information from the engineering for Max Fordham and
they did an analysis from twenty eighteen of yak Child's
and just how effective they might have been. And they
found that the walls of a yak chaw had the
same insulative properties as a wall of concrete three inches
(02:47):
thick surrounded by a one foot thick wrapping of styrofoam insulation.
That's how effective these things were.
Speaker 2 (02:55):
Sand, clay, egg whites, lime, and goat hair and ash.
Speaker 1 (02:59):
I was gonna say, like the secret egg whites, but
who knows you throw goat hair in there, and yeah,
who knows what the secret? I think the secret is
the whole thing together, the whole say rouge mysture?
Speaker 2 (03:13):
Yeah, probably so so I mentioned that sometimes the ice
was brought in from the mountains and kept there throughout
the year. But usually what would happen is is they
would make ice, They would bring in water. They would
divert water from an aqueduct through these underground water channels
called cannots, and they would channel them to the north
(03:35):
side of this wall. It's another thing we haven't mentioned
yet is they have these very very high walls that
act as shade for these channels to keep you know,
the wind off of it, because stuff isn't going to
freeze as fast if it's moving, so to keep the
water still and to keep it cooler away from that sun.
Speaker 1 (03:56):
Yeah, And so the channel has a little diversion into
a trench or a pit or like a very shallow
like rectangular pond usually, and it they'll divert water in
there to fill it up, and then they let it
freeze overnight. Over the course of a few nights, it'll
continue to freeze and freeze and freeze in layers. And
(04:18):
the what they're taking advantage of, you know, like when
it snows and then the temperatures heat up and all
the snow melts, but there's a little pile of snow
like in a shaded corner of your yard that never
gets direct sunlight. Yeah, and it just takes forever to melt.
There can be advantage of the same thing. They're building
that big old that big old wall to keep it
shaded and to just let this ice grow and grow
(04:41):
and grow. And then once it reaches I think fifty centimeters,
which is like about a half a meter thick, then
they'll cut it into blocks and they put it in
the yac shell and they store it through summer. Like
this stuff will stay frozen for an entire summer. So
in in that sense, these yak chails are built to
(05:02):
store cold throughout the course of a year, even when
the summer comes around still cold.
Speaker 2 (05:09):
Yeah. Another way that helps us out is that dome shape.
It's not domed because they like domes, even though domes
are nice. It's conical because that optimizes what's called the
solar chimney effect. Is that's when you create a convection current,
letting that heat go up, up, up and out through
these openings at the top and bringing in that cool
air from the bottom.
Speaker 1 (05:29):
They also have wind catchers that they call bad geers,
and they actually take win and direct it downward into
the yakchaw dome. And so the air that hits it
is cooled by that ice, and the air that's not
cool by it, or cooled enough, like you said, that
chimney effect takes it up along the curve sides toward
(05:49):
the hole in the top, and it says, see you later,
don't come back.
Speaker 2 (05:53):
That's right, And that feels like a good time for
a break, and we'll come back and talk about what
the heck they're doing with all this ice. This all right,
(06:27):
So they're making ice, they're preserving ice. What are they
doing with all this ice? One of the things they're
doing is using it as a refrigerator. You know, they'll
store food in there that they don't want to go bad,
and just using it as a as a cold house.
They will also just use the ice to eat in
a treat. They have something called Feluda over there, to
(06:51):
Persian traditional dessert has thin vermicelli noodles made from cornstarch,
and then you mix that up with a little semi
frozen sirr of sugar and rose water, and then serve
it up with a little lime juice and maybe some
ground pistachios. And it's like a little Persian icy.
Speaker 1 (07:09):
That has to be better than it sounds, don't you think?
Speaker 2 (07:11):
Oh I think it sounds great.
Speaker 1 (07:13):
I think the pistachos are where of throwing me off.
Speaker 2 (07:16):
Oh yeah, you don't like pistashios.
Speaker 1 (07:18):
Or I do like pisachos. It just they don't seem
to go with the rest of the ingreen eent. But
like I said, I'm sure it's delicious. I mean, it's
a traditional Persian dessert. It's got staying power. So yeah,
who am I to question for luda exactly?
Speaker 2 (07:32):
I bet it's delicious.
Speaker 1 (07:34):
One of the cool things about this is that yak
charles I mean, and there's some still around. I think
there's one in Kerman, Iran that's about the size of
a five story building. So you would think, of course,
obviously this was reserve for royalty. You would be dead wrong,
because not only were yakchels open and available to the public,
(07:56):
there are some that people just built for their houses
that were a private use of as well.
Speaker 2 (08:00):
Yeah, for sure, they would make those delicious falluda. They
would make surbets and preserve them and then nuts, fruit
and ice and they would put them on a donkey
and go sell them at market and stuff like that.
They would sell ice directly from those places sometimes. And
you know, one of the things they're also taking advantage
(08:22):
of is the greenhouse effect. You know, the earth is
going to stay fairly warm at night because of the
greenhouse effect trapping those gases in the atmosphere. But if
it's low humidity and if it's a really clear night,
that effect is going to be weaker and that heat
can dissipate and disappear more readily. And so that's when
they discovered, like, hey, we can make these little thin
(08:44):
layers of ice and kind of build, you know, day
by day, night by night on these clear, low humidity nights,
eventually to get you know, some pretty significant ice.
Speaker 1 (08:53):
And once they figure that out, someone said, go get
the donkey. Exactly, it's time to sell some Subert and
harvesome goat hair. One other thing I saw in that
Max Fordham analysis, they figured out that they could make
about what would be equivalent to three million ice cubes
a season.
Speaker 2 (09:12):
Wow.
Speaker 1 (09:13):
Yeah, which is a lot. But they were like, you'd
think it'd be more, and I was like, it seems
pretty good to me, especially in four hundred BC.
Speaker 2 (09:20):
You know, it depends on how big those cubes were.
Were they big fancy cocktail cubes. That's a lot more
ice than a ice nugget.
Speaker 1 (09:27):
That's right, You're absolutely right. I expect that they're probably
all donkey head size. So three million donkey head size
ice cubes, that's big. Think about the poor donkey that
had to cart those around. I know, no fun, you
got anything else?
Speaker 2 (09:43):
Yeah, I mean these went away obviously because of modern
refrigeration came on the scene. And also one thing that
was happening was they were making this ice kind of
out in the open, and a lot of it would
get contaminated with dust and it wasn't like the healthiest
ice in the world. And so that combined with modern
refrigeration coming along, they're like, maybe we should just not
(10:04):
have these much anymore. But like you mentioned, there is
one still around, at least in Kerman, and there are
groups there that are trying to preserve this way of
life and at least keep it, you know, not like
a chief refrigerating method, but like, hey, we can't lose
our culture, and so let's work to take some of
these old ones and restore them at least, even if
(10:25):
only for like museum and touring purposes.
Speaker 1 (10:28):
For sure, but also there's a lot to learn from them,
especially when we're trying to advance like passive cooling and
other things that require less energy to cool things down.
Yak Chaal's are something to turn to and say how
do we do this? And someone says, go get the
goat here.
Speaker 2 (10:44):
That's right, we'll get some egg whites too. No one
likes this.
Speaker 1 (10:48):
What do we do with all these yokes? Yeah, well,
I think that's it for short stuff, right, Chuck?
Speaker 2 (10:54):
I think so?
Speaker 1 (10:55):
Well? I mean short stuff is that.
Speaker 2 (11:00):
Stuff you Should Know is a production of iHeartRadio. For
more podcasts my iHeartRadio, visit the iHeartRadio app, Apple Podcasts,
or wherever you listen to your favorite shows.
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