Short Stuff: Yakhchāls - Ancient Fridges

Summary

Stuff You Should Know: Short Stuff – Yakhchāls - Ancient Fridges
Released on February 12, 2025 | Hosts: Josh Clark & Chuck Bryant | Produced by iHeartPodcasts

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Introduction to Yakhchāls

In the episode titled "Short Stuff: Yakhchāls - Ancient Fridges," hosts Josh Clark and Chuck Bryant delve into the fascinating world of Yakhchāls—ancient refrigeration systems used in Persia around 400 BC and still present today in regions like Iran, Afghanistan, and Tajikistan. These ingenious structures have intrigued engineers, historians, and physicists alike due to their remarkable ability to preserve ice and food without modern technology.

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Historical Context and Geographical Spread

The discussion begins with an exploration of the origins and enduring presence of Yakhchāls. Josh and Chuck highlight that these ancient refrigerators were not exclusive to royalty; they were accessible to the public and even found as private installations in individual homes.

Josh Clark [01:35]: "Apparently still today in Iran, Afghanistan and Tajikistan. Tajikistan. Yeah, I said it right the first time. They call the refrigerators yakchals, which is how I would say it if I were in Iran."

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Construction and Insulation Techniques

A significant portion of the episode focuses on the sophisticated construction of Yakhchāls, particularly their insulation capabilities. The walls of a Yakhchāl are composed of a mortar called ceruge, a mixture of sand, clay, egg whites, lime, goat hair, and ash.

Chuck Bryant [02:41]: "Sand, clay, egg whites, lime, goat hair and ash. Quite a mixture."

Josh references a 2018 analysis by the engineering firm Max Fordham, which found that the walls of a Yakhchāl provided insulation equivalent to a 3-inch thick concrete wall wrapped in a foot of Styrofoam. This exceptional insulation allowed Yakhchāls to maintain cold temperatures even during scorching summers.

Josh Clark [02:51]: "They found that the walls of a yakcha had the same insulative properties as a wall of concrete 3 inches thick, surrounded by a 1 foot thick wrapping of Styrofoam insulation."

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Ice Production and Preservation Methods

The hosts explain the ingenious methods used to produce and preserve ice in Yakhchāls. Ice was either mined from mountains and stored year-round or produced on-site by diverting water through underground channels called kanats to the north side of the Yakhchāl. The water would flow into shallow ponds, freezing layer by layer over several nights.

Chuck Bryant [04:24]: "They would 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."

The Yakhchāl’s design, including its high, conical shape, facilitated the solar chimney effect, creating convection currents that expelled warm air and drew in cooler air, enhancing the cooling efficiency.

Chuck Bryant [05:37]: "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."

Additionally, wind catchers known as bajeers directed cool air downward into the Yakhchāl, further aiding in maintaining low temperatures.

Josh Clark [06:07]: "They also have wind catchers that they call bajeers, and they actually take wind and direct it downward into the Yakchal dome."

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Uses of Yakhchāls in Society

Yakhchāls served multiple purposes beyond ice storage. They were used as cold storage for food preservation and as refrigerators for perishable items. The hosts also discuss cultural uses, such as the preparation of falooda, a traditional Persian dessert made with semi-frozen syrup, vermicelli noodles, rose water, lime juice, and pistachios.

Chuck Bryant [08:32]: "They also just use the ice to eat a treat. They have something called falooda over there... it’s like a little Persian icy."

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Decline and Preservation Efforts

With the advent of modern refrigeration, Yakhchāls began to fall out of use. Challenges like ice contamination from dust and the labor-intensive process of ice production contributed to their decline. However, efforts are underway to preserve these historical structures. For instance, a notable Yakhchāl in Kerman, Iran, remains operational and is a focus of restoration projects to maintain cultural heritage.

Chuck Bryant [12:09]: "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."

The hosts emphasize the potential lessons modern engineering can learn from Yakhchāls, especially in areas like passive cooling and energy-efficient refrigeration.

Josh Clark [12:54]: "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."

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Cultural and Societal Impact

The episode concludes with a light-hearted discussion about the societal aspects of Yakhchāls, such as the use of ice in traditional foods and the communal effort in ice production. The hosts humorously ponder the logistics of transporting large quantities of ice and the role of animals like donkeys in these ancient practices.

Chuck Bryant [11:19]: "And so they discovered, like, hey, we can make these little thin layers of ice and kind of build... eventually to get... some pretty significant ice."

Jess Clark [11:38]: "Which is a lot. But they were like, you'd think it'd be more."

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Conclusion

Short Stuff: Yakhchāls - Ancient Fridges offers an engaging exploration of Yakhchāls, highlighting their historical significance, architectural ingenuity, and cultural impact. Through detailed discussions and insightful quotes, Josh and Chuck provide listeners with a comprehensive understanding of how these ancient refrigeration systems functioned and their relevance to both past and present societies.

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Notable Quotes with Timestamps:

• Chuck Bryant [02:41]: "Sand, clay, egg whites, lime, goat hair and ash. Quite a mixture."

• Josh Clark [02:51]: "They found that the walls of a yakcha had the same insulative properties as a wall of concrete 3 inches thick, surrounded by a 1 foot thick wrapping of Styrofoam insulation."

• Chuck Bryant [05:37]: "Another way that helps us out is that dome shape... it's conical because that optimizes what's called the solar chimney effect."

• Josh Clark [06:07]: "They also have wind catchers that they call bajeers, and they actually take wind and direct it downward into the Yakchal dome."

• Josh Clark [12:54]: "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."

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For more insights into intriguing topics, explore other episodes of Stuff You Should Know available on the iHeartRadio app, Apple Podcasts, or your preferred podcast platform.

Transcript

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[Josh Clark]

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

[Chuck Bryant]

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

[Josh Clark]

Hmm. I'm going with the straight ahead. Yakhchals.

[Chuck Bryant]

All right.

[Josh 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.

[Chuck Bryant]

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 400 BC. This is modern day Iran. And 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.

[Josh 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 the refrigerators yakchals, 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 Yakchal.

[Chuck Bryant]

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 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. From a mortar called ceruge.

[Josh Clark]

Oh, is that how you're saying it?

[Chuck Bryant]

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

[Josh Clark]

Some of these were several meters thick, some of These yakchals were. But there was a study. We got some of this information from the engineering firm Max Fordham, and they did an analysis from 2018 of yakchals and just how effective they might have been. And they found that the walls of a yakcha had the same insulative properties as a wall of concrete 3 inches thick, surrounded by a 1 foot thick wrapping of Styrofoam insulation. That's how effective these things were.

[Chuck Bryant]

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

[Josh Clark]

I was going to say, like, the secret is 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 seiruj mixture.

[Chuck Bryant]

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 kanats, 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.

[Josh 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. And it just takes forever to melt. They're taking advantage of the same thing. They're building 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 yakchel and they store it through summer. Like this stuff will stay frozen for an entire summer. So in that sense, these yakchels are built to store cold throughout the course of a year, even when the summer comes around, still cold.

[Chuck Bryant]

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. 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.

[Josh Clark]

They also have wind catchers that they call bajeers, and they actually take wind and direct it downward into the Yakchal 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 it says, see you later. Don't come back.

[Chuck Bryant]

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.

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[Chuck Bryant]

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 cold house, they will also just use the ice to eat 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 rose water. And then. And then serve it up with a little lime juice and maybe some ground pistachios. And it's like a little Persian icy.

[Josh Clark]

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

[Chuck Bryant]

Oh, I think it sounds great.

[Josh Clark]

I think the pistachios are what are throwing me off.

[Chuck Bryant]

Oh, yeah, you don't like pistachios or.

[Josh Clark]

I do like pistachios. It 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, yeah, who am I to question faluda?

[Chuck Bryant]

Exactly. I bet it's delicious.

[Josh Clark]

One of the cool things about this is that yakchals, 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 yakchels open and available to the public, there were some that people just built for their houses that were of private use as well.

[Chuck Bryant]

Yeah, for sure. They would make those delicious falooda, they would make sherbets and preserve them. Isn't that 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 one of the things they're also taking advantage of is the greenhouse effect. 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.

[Josh Clark]

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

[Chuck Bryant]

Yeah, exactly.

[Josh Clark]

It's time to sell some sherbet and.

[Chuck Bryant]

Harvest some goat hair.

[Josh 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.

[Chuck Bryant]

Wow.

[Josh 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 if in 400.

[Chuck Bryant]

BC, you know, depends on how big those cubes were. Were they big, fancy cocktail cubes? That's a lot more ice than a ice nugget.

[Josh 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, that's big. Think about the poor donkey that had to cart those around.

[Chuck Bryant]

I know, no fun.

[Josh Clark]

You got anything else?

[Chuck Bryant]

Yeah, I mean, these went away obviously because of modern refrigeration came on the scene. And also a 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 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 for sure.

[Josh Clark]

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

[Chuck Bryant]

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

[Josh Clark]

What do we do with all these yolks?

[Chuck Bryant]

Yeah.

[Josh Clark]

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

[Chuck Bryant]

I think so.

[Josh Clark]

Well, that means short stuff is that.

[Chuck Bryant]

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