Sound Bites: Swetha Sivakumar on the history of refrigeration

We unlocked the secret to making ice less than 200 years ago. See how different cultures found ingenious ways to gather, store and use ice over the years.

Look around the kitchen. Every gadget there, whether microwave, oven, pressure-cooker or air fryer, aims to heat something up in a different way.

According to the National Family Health Survey (NFHS-5), just under 38% of Indian households, for instance, owned a refrigerator as of 2019-21. (.)

The refrigerator is the only thing that cools.

We may not notice this core difference any more, but it is a big deal.

Humans, after all, have controlled fire for over 100,000 years. We unlocked the secret to making ice less than 200 years ago.

It is such a recent win, in fact, that much of the world still doesn’t fully share in its benefits.

According to the National Family Health Survey (NFHS-5), just under 38% of Indian households, for instance, owned a refrigerator as of 2019-21.

Still, long before compressors and electricity, cultures around the world had found ingenious ways to gather, store and use ice. In the Mediterranean and South America, people harvested it from the Alps and Andes, as large blocks. These were wrapped in insulating straw or sawdust and carted to the cities.

As far back as 1750 BCE, Mesopotamia had thick-walled, well-insulated ice houses along the Euphrates, where such slabs were stored. In Russia, ice from the Neva River supplied Saint Petersburg for centuries.

It was in Ancient Persia, c 400 BCE, that humans first began to make ice, outdoors, and using ambient cold. In the dry desert air and cold nights of this region, yakhchāls or massive domed structures were built, of thick, insulating mudbrick. Shallow pools of water were installed nearby. As the air cooled, the temperature of the water dipped below freezing. By morning, thin sheets of ice had formed, which were harvested and stored in the yakhchāls. Many of these structures still stand in Iran, a testament to the ingenuity of ancient engineers.

In India, meanwhile, a unique cooling technique was used during the Mughal era, in the 17th century. Chemists discovered that potassium nitrate, a type of saltpeter, could be packed around an urn that needed chilling. As the salts dissolved, they drew heat from their surroundings. This was the energy that went into breaking up their crystal-lattice formation.

It was clever but not scalable, since saltpeter was a limited resource and was needed for gunpowder, fertiliser and meat preservation. Still, it foreshadowed the modern ice pack, and was a creative workaround in the punishing summers of north India.

The real leap in refrigeration came in 1748, via the Scottish physician William Cullen.

Experimenting with volatile fluids, he demonstrated that certain liquids absorbed dramatic amounts of heat from their surroundings, as they evaporated.

If he could deploy a fluid with a boiling point far below room temperature in an enclosed space, Cullen figured, it could generate blasts of cool air. And wouldn’t that be useful?

He was right, of course.

The chemical isobutane is one such compound. It has a boiling point of about -11 degrees Celsius; newer refrigerants have boiling points as low as -30 degrees Celsius. This allows a refrigerator to draw heat from the objects and air within it, lowering this internal temperature significantly as the liquid coolant evaporates into gas. Its compressor coils can then release that absorbed energy as mild heat released into the air around the device. Meanwhile, the gas cools and condenses into liquid form and the cycle begins again.

The choice of refrigerant has defined each era of this technology.

Ammonia worked well but was toxic, making leaks dangerous. Chlorofluorocarbons replaced ammonia and were safe, but released chlorine into the air that ate away at the ozone layer. Hydrofluorocarbons were ozone-friendly, but had a far greater global-warming effect than even carbon-dioxide.

The latest evolution has involved hydrofluoroolefins (a compound of hydrogen, fluorine and carbons), which are more efficient and have a lower global-warming impact than their predecessors. Since the 2010s, they have been increasingly adopted worldwide.

All this has made it is easy to take refrigeration for granted today, but it has been one of humanity’s most transformative technologies.

In the arena of healthcare, its cold-chain capabilities keeps vital medicines viable while its low temperatures reduce germs in operation theatres and intensive-care units.

Refrigeration decoupled food from seasons and geography. Milk could be shipped across countries, supermarkets could stock oranges all year round. A web of refrigerated warehouses, trucks and shipping containers now underpin modern civilisation.

The climate costs, of course, are immense.

Journalist and James Beard awardee Nicola Twilley captures this dramatically in her book Frostbite (2024). She points to Norse mythology, where even the gods perish in a world-ending apocalypse called Ragnarok (Norse for Fate of the Gods).

“As the new Artic we have built for our food plays its part in melting the old Artic faster than anyone could have imagined,” she writes, “we had better muster the collective wisdom and action to avoid their fate.”

(To reach Swetha Sivakumar with questions or feedback, email upgrademyfood@gmail.com. The views expressed are personal)