A Story About Salt

1. The Number Under the Tub

I stopped by my parents' house and came back with a tub of baendaengi jeotgal (jeotgal is the Korean name for seafood fermented in salt, and baendaengi is a small, sardine-like fish that goes into it whole). It had been wrapped in layer after layer of yellow plastic bags, and to fit it in the fridge I needed something to move it into, so I pulled a few food containers out of the cupboard and turned them over. Every one had a number stamped inside a triangle of arrows.

Baendaengi jeotgal, small salted fish, in a yellow plastic bag — Salted fish from my parents’ house. It came in plastic from the start.

That number is the resin code: 1 is PET, 2 is HDPE, 3 is PVC, 4 is LDPE, 5 is PP, 6 is PS, and 7 is everything else. Jeotgal is salty and oily and it sits in the fridge for a long time, so the ones that hold up under those conditions are 2 (HDPE) and 5 (PP), while 3 (PVC) and 6 (PS) are poor fits. The hard, clear containers people use for side dishes are usually PS, which is why gimchi (Korea's everyday fermented vegetables, most often napa cabbage salted and then seasoned with chili, garlic and fish sauce) and jeotgal are better kept out of them.

Flip over one of Daiso's vacuum containers and you'll find a 1, PET, because it has to be see-through and rigid enough not to buckle when the air is pumped out. A container's material is chosen for the job the container has to do, more than for the food that goes in it.

So is a number 5 PP tub the end of it? Not quite. The heat rating printed on a PP tub means the tub keeps its shape up to that temperature, not that nothing leaches out up to that temperature, and a 2020 study in Nature Food showed that PP baby bottles shed microplastics in huge numbers when hot water is poured in to mix formula. This is where choosing by label runs out. What's left, if you want to choose without reading any label at all, is ceramic or glass, and since ceramic glazes can be a problem and you'd have to check whether each piece is food-grade, glass is what remains. Jeotgal lives in the fridge, so it doesn't need to stand up to heat, but for an all-purpose container that also has to take hot food, the last one standing is heat-resistant glass. So the jeotgal went into a glass jar.

2. The Lining Inside the Can

Among the ways we store food there's one issue people in the know already know about: BPA-free cans. Before that issue took off, nearly all canned food was packed in cans whose inner metal surface was coated with epoxy resin, and the raw material of that coating is bisphenol A. That's where the question comes from: when you open a can of mackerel or saury, should you pour off the liquid?

BPA became a problem because it behaves like estrogen, a female sex hormone, inside the body. Its structure resembles estrogen closely enough to bind to estrogen receptors, so the body receives a hormonal signal it never sent, which is why BPA is classed as an endocrine disruptor. The stages of life most sensitive to hormonal signals are the fetus and early childhood, so regulation started with baby bottles and containers for infants. Cans are sterilized at high temperature with the food already inside, and canned fish also sits in oil and salt, so the question of how much moves from the coating into the food ends up centered on the liquid in the can.

The answer depends on the country. In the EU, EFSA cut its tolerable daily intake for BPA to one twenty-thousandth of the previous value in 2023, and in December 2024 the EU adopted a regulation banning BPA in food contact materials. Korea keeps a migration limit of 0.6 ppm, and its outright ban stopped in 2018, when it was extended to all products for infants and toddlers. The US never banned it by law, but consumers avoided it, the market moved, and manufacturers changed the coatings on their own.

Search Korean products for a BPA-free label and you'll find posts mentioning Dongwon's canned tuna and nothing confirming it for canned mackerel or Korean-made Spam. And BPA-free doesn't mean plastic-free. The replacement coatings are plastic too, and in some cases BPA is swapped out for structurally similar BPS or BPF, so pulling one name off the list just lets the name next to it take its place.

3. The Shield in the Paper

You'd think paper would be better off, but it depends on the use. A milk carton has a PE lining inside the paper, and PE is relatively stable, so there's little to worry about there; the trouble is paper that has to keep grease from soaking through. Burger wrappers were long treated with PFAS, per- and polyfluoroalkyl substances, to hold the grease back, and in 2024 the US FDA announced that grease-proofing PFAS for food packaging were no longer being sold on the US market.

Wrappers differ from tubs and cans in that the consumer has no say at all. You can switch containers and pour off the can liquid yourself, but a burger comes out of the warming cabinet already wrapped, so you take the wrapper you're given.

PFAS get their strength from the carbon-fluorine bond, one of the strongest bonds in organic chemistry. That's why neither grease nor water can get through, and for the same reason they don't break down in nature. Resisting everything and never breaking down aren't two properties; they're two faces of one bond.

4. The Same Shape, Again

Go back to PP and the same shape shows up. PP is light, tough and cheap, so more of it is made than any other plastic, and it breaks up easily in sunlight, but even after it breaks up it doesn't go away; it just keeps turning into smaller pieces, and those pieces are microplastics. It doesn't decompose, it crumbles in sunlight, and it's made in huge volumes. Those three together make PP a main source of microplastics.

Fluorine is so hard it never goes away, and PP breaks apart but never goes away, so in both cases the property that makes them useful is the very property that makes them a problem. What flexes easily leaches easily, and what blocks well lingers well, and since these are two sides of one structure, you can't keep the good side and leave the other.

Pieces that don't go away keep splitting. Once microplastics break down below one micrometer they're called nanoplastics, and because the usual analytical methods struggle to catch particles below a few micrometers, pieces this small tend to slip out of the measurements. How they act in the human body is still under study, but reports keep coming in of them being found in blood, placentas, blood vessels and the brain, and a 2025 study in Nature Medicine reported that the amount found in the brains of the deceased was markedly higher in 2024 samples than in 2016 samples.

5. Salt

So where do the pieces that wash into the sea end up? In 2018, Incheon National University and Greenpeace tested 39 salt brands sold in 21 countries and found microplastics in 36 of them, and the highest counts came from sea salt, made by drying seawater. In Korea that salt is cheonilyeom (sun-dried sea salt, made by letting sun and wind evaporate seawater in open salt pans on the coast, and the salt most Korean households reach for when they ferment food).

Jugyeom (bamboo salt, a traditional Korean salt sold at premium prices as a health product) is made by packing sea salt into bamboo stalks and roasting it at high temperature, so any plastic burns away. But burning leaves combustion byproducts and ash behind, and jugyeom's distinctive smell is itself evidence that something burned and left a residue.

Rock salt mined from the ground never went through what the sea is going through today, and its pink or reddish color comes from iron oxide. It has the opposite problem, minerals mixed in with it, and one pink salt sold in Australia was found with lead above the national limit.

That leaves refined salt. Seawater is filtered through ion-exchange membranes so only sodium chloride is drawn out, which means microplastics and minerals are both left behind, and this cleanest salt is, if anything, the cheapest. Cheonilyeom sells as a premium product on the strength of minerals and tradition, refined salt is treated as cheap because it looks like factory salt, and in Korea one large company dominates the refined salt market.

Think about it a little and something looks off. The story that cheonilyeom is best for gimjang (the late-autumn event when a household makes its whole winter supply of gimchi at once, salting cabbages by the dozen) comes from the magnesium in its gansu (bittern, the bitter, magnesium-rich liquid that drains out of sea salt as it sits), which is said to keep the cabbage firm; what that story leaves out is the plastic mixed into the same salt, and the fact that magnesium can be added to refined salt with a light bit of processing.

Jugyeom is the same. The talk about its health benefits is thick with pseudoscience, and if any component in it is actually useful, that component too could be added to refined salt more safely, the way magnesium is for gimjang salt.

Cheonilyeom and jugyeom carry whatever is mixed into their raw material and advertise the good parts, while refined salt clears out what's mixed in first and can then have exactly what's needed added back. By my review, a modified salt built on refined salt, with the needed components added, is the best answer.

6. Back to the Jeotgal

When I put the jar of jeotgal in the fridge and looked back, I'd started from the number under a tub and come through can linings and fluorine in wrappers all the way to salt.

At every step the call was made the same way. Follow the stories on labels and health claims and there's no end to it, but pick a base that nothing can seep into first and add what you need on top, and there is an end: for containers the base was heat-resistant glass, and for salt it was refined salt.

The property that makes something useful and the property that makes it a problem could never be pulled apart, so whenever a story sells you on a good property, ask first what's on the back of it. What does something that blocks so well leave behind? What else comes in alongside the ingredient that's supposed to be good for you?

I look into the glass jar I chose that way. Baendaengi jeotgal is cured in salt, and the salt used for jeotgal is cheonilyeom.