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

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.

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."

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."

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."

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."

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."

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."

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.

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."

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.