Short Stuff: Yakhchāls - Ancient Fridges

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. See omnystudio.com/listener https://omnystudio.com/listener for privacy information.

Speaker names marked ? are inferred from speaking time and the show’s known hosts — they are not voice-verified.

• 0:00Speaker 00

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• 0:04Josh Clark?

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• 0:39Josh Clark?

  Hey, and welcome to the Short Stuff. I'm Josh, and there's Chuck, Jerry sitting in for Dave. And so this is Short Stuff, the how do you say this again edition?

• 0:48Speaker 02

  Yeah, I'm gonna say it's pronounced, spelled Y-A-K-H, you know, as most words are. C-H-A-A-L. I'm gonna say Yakals.

• 1:00Josh Clark?

  I'm going with the straight-ahead Yakchals.

• 1:03Speaker 02

  All right.

• 1:04Josh Clark?

  Okay. So you say it your way throughout, I'll say it my way, and I'm sure I'll inevitably, unconsciously, start saying it your way.

• 1:12Speaker 02

  We'll see. But what we're talking about is the, 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 400 B.C. This is modern-day Iran. And this is, these are places where, believe it or not, the climate enables freezing of ice when you would not think you should be able to freeze ice.

• 1:42Josh Clark?

  Yeah, it's pretty amazing. And apparently, still today, in Iran, Afghanistan, and Tajikistan, Tajikistan, yeah, I said it right the first time, they call their refrigerators Yakchals, which is how I would say it if I were in Iran. But that's the name for their fridge, which means that at some point, someone in Iran has gone into a store and said, "You got a smeg Yakchow?"

• 2:06Speaker 02

  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...

• 2:19Speaker 02

  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 I know goes a long way toward keeping this ice. And we got to say, some of this ice is mined from the mountains and 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 serouge.

• 2:48Josh Clark?

  Was that how you say in it?

• 2:50Speaker 02

  Yeah, sand, clay, egg whites, lime, goat hair and ash. Quite a mixture.

• 2:58Josh Clark?

  Some of these were several meters thick, some of these yak chals were. There was a study, we got some of this information from the engineering for Max Fordham. And they did an analysis in 2018 of yak chals and just how effective they might have been. And they found that the walls of a yak chal had the same insulating properties as a wall of concrete, three inches thick, surrounded by a one foot thick wrapping of styrofoam insulation. That's how effective these things were.

• 3:30Speaker 02

  Sand, clay, egg whites, lime and goat hair and ash.

• 3:34Josh Clark?

  I was gonna say like the secret is egg whites, but.

• 3:37Speaker 02

  Who knows?

• 3:38Josh Clark?

  You throw goat hair in there and.

• 3:39Speaker 02

  Yeah.

• 3:41Josh Clark?

  Who knows what the secret, I think the secret is the whole thing together, the whole serouge mixture.

• 3:48Speaker 02

  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 canots. And they would channel them to the north 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.

• 4:31Josh Clark?

  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 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 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.

• 5:05Speaker 02

  Yeah.

• 5:05Josh Clark?

  And it just takes forever to melt.

• 5:07Speaker 02

  That was our yard.

• 5:08Josh Clark?

  They're taking advantage of the same thing. They're building that big old, that big old wall to keep it shaded and just let this ice grow and grow and grow. And then, once it reaches, I think, 50 centimeters, which is like about a half a meter thick, then they'll cut it into blocks and they put it in the yak chal and they store it through summer. Like this stuff will stay frozen for an entire summer. So in that sense, these yak chals are built to store cold throughout the course of a year. Even when the summer comes around, it's still cold.

• 5:44Speaker 02

  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.

• 6:04Josh Clark?

  They also have wind catchers that they call bajirs. And they actually take wind and direct it downward into the yak chal dome. And so the air that hits it is cooled by that ice and the air that's not cooled by it or cooled enough, like you said, that chimney effect takes it up along the curved sides toward the hole in the top and says, "See you later, don't come back."

• 6:28Speaker 02

  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, right after this.

• 6:49Speaker 02

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• 7:44Speaker 02

  All right, 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 coldhouse. They will also just use the ice to eat and a treat. They have something called falooda over there. It's a Persian traditional dessert, has thin vermicelli noodles made from cornstarch. And then you mix that up with a little semi-frozen syrup of sugar and rosewater, and then serve it up with a little lime juice and maybe some ground pistachios. And it's like a little Persian icy.

• 8:26Josh Clark?

  That has to be better than it sounds, don't you think?

• 8:29Speaker 02

  Oh, I think it sounds great.

• 8:30Josh Clark?

  I think the pistachios are what are throwing me off.

• 8:33Speaker 02

  Oh, yeah? You don't like pistachios, or?

• 8:35Josh Clark?

  I do like pistachios, it's just they don't seem to go with the rest of the ingredients. But like I said, I'm sure it's delicious. I mean, it's a traditional Persian dessert. It's got staying power, so.

• 8:46Speaker 02

  Yeah.

• 8:47Josh Clark?

  Who am I to question falooda?

• 8:49Speaker 02

  Exactly. I bet it's delicious.

• 8:51Josh Clark?

  One of the cool things about this is that yak chals, 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 reserved for royalty. You would be dead wrong, because not only were yak chals open and available to the public, there were some that people just built for their houses that were of private use as well.

• 9:18Speaker 02

  Yeah, for sure. They would make those delicious falooda. They would make sherbets and preserve them.

• 9:24Josh Clark?

  Isn't that nuts?

• 9:25Speaker 02

  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 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 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.

• 10:11Josh Clark?

  And once they figured that out, someone said, "Go get the donkey."

• 10:14Speaker 02

  Yeah, exactly.

• 10:15Josh Clark?

  It's time to sell some sherbet.

• 10:18Speaker 02

  And harvest some goat hair.

• 10:19Josh Clark?

  One other thing I saw in that Max Fordham analysis, they figured out that they could make about what would be equivalent to 3 million ice cubes a season.

• 10:29Speaker 02

  Wow.

• 10:30Josh Clark?

  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 400 B.C., you know?"

• 10:38Speaker 02

  Depends on how big those cubes were. Were they big fancy cocktail cubes? That's a lot more ice than an ice nugget.

• 10:44Josh Clark?

  That's right. You're absolutely right. I expect that they're probably all donkey head size. So 3 million donkey head size ice cubes.

• 10:53Speaker 02

  That's big.

• 10:54Josh Clark?

  Think about the poor donkey that had to cart those around.

• 10:56Speaker 02

  I know. No fun.

• 10:58Josh Clark?

  You got anything else?

• 11:00Speaker 02

  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 were like, maybe we should just not 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 only for like museum and touring purposes.

• 11:45Josh Clark?

  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 chals are something to turn to and say, how do we do this? And someone says, go get the goat here.

• 12:01Speaker 02

  Yeah, that's right. With get some egg whites, too. No one likes those.

• 12:04Josh Clark?

  Right. What do we do with all these yolks?

• 12:07Speaker 02

  Yeah.

• 12:08Josh Clark?

  Well, I think that's it for short stuff, right, Chuck?

• 12:11Speaker 02

  I think so.

• 12:12Josh Clark?

  Well, that means short stuff is it.

• 12:17Speaker 03

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