Korean cooking runs on two seed oils, and they are not interchangeable. Sesame oil, pressed from roasted sesame seeds, is amber, deep, and toasty, the smell most people know from bibimbap. Perilla oil, pressed from the roasted seeds of the perilla plant, kin to mint and Japanese shiso and called deulkkae in Korean, is paler, grassier, and gentler on the tongue, the oil Korean cooks pour over cold buckwheat noodles and brush onto sheets of seaweed. Sesame is the bold one and perilla the soft one, and they also age at very different speeds, which is why anyone asking how to store perilla oil gets a different answer than for sesame oil.
On an American grocery shelf, the olive oil comes by the liter, sometimes by the gallon tin, and right beside it sits a bottle of Korean sesame oil small enough to close your hand around. Most shoppers read that as price. In a Korean kitchen it reads as a warning: these oils are alive, and they will not wait for you. Sesame oil is sturdy enough to live in the cupboard, while perilla oil turns so quickly that most Korean households keep it in the refrigerator door. Buy small, finish soon, and keep the green one cold; the small bottle is not a limitation of the product but the whole method.
I learned the method long before I understood it. The smell of sesame oil hitting a hot pan is still the fastest way back into my mother's kitchen, and her oil never sat long enough to go stale. Every autumn, the bottles came home small and fresh, from a place most American kitchens have never had: the neighborhood mill.
Two Oils, Two Clocks
The bangatgan, the neighborhood grain mill, is one of the oldest working rooms in a Korean market. It is where families have long brought rice to be milled and steamed into rice cakes for a holiday, dried chilies to be ground for winter kimchi, and, every autumn, their own sesame and perilla seeds to be roasted and pressed. Not far from where I live there is still a market alley where, from late September on, the air turns warm and brown by mid-morning. You smell the mill before you see it.
The timing is the crop's, not the mill's. Sesame comes in first, harvested in late summer. Perilla flowers only as the days shorten, around early September, and its seeds ripen into autumn, so the new perilla arrives just as the weather turns.
That is when people line up at the mill with plastic bags of their own seed, sometimes grown in a parent's field in the countryside, and wait while the roaster turns. Then the roasted seed goes into the press, and the oil runs out dark gold and thin, into whatever bottles the family brought, with no label at all.
What they carry home is never a gallon. It is two or three small bottles, still faintly warm. Nobody asks the miller how long it keeps. Everyone already knows.
Koreans half-joke about a gochugaru cartel, the quiet network through which the best chili powder travels from a relative's field to a mill to a family's kimchi without ever touching a store shelf. Sesame and perilla oil move the same way, and if anything the circle is tighter. The best bottle in a Korean kitchen usually carries no brand at all. It was pressed from seed an aunt grew behind her house, roasted at the mill on a morning she chose, and handed over in a rinsed-out soju bottle with a twist of plastic under the cap. You cannot buy it; you can only be given it, or be related to someone who grows it.
And the oil from home-grown seed, pressed the day it is roasted, tastes like nothing on a store shelf. Sesame comes out so deeply nutty it is almost sweet. Perilla is green enough to smell from across the table, with a roundness that coats the rice and then lets go. Once you have had a spoonful from a bottle like that, you understand why a Korean family will drive half a day to collect it, and why nobody gives it away to just anyone.
That bottle tastes alive partly because it is young. Roasting is where the flavor comes from, and it is also where the clock starts. Raw sesame and perilla seed taste mild and flat; the roast builds the deep, nutty aroma Korean cooking depends on. The moment that oil is pressed, though, it begins to meet the air. And the two oils meet it very differently, which is the reason one lives in the cupboard and the other in the fridge.
Perilla oil is rich in alpha-linolenic acid, a fatty acid that reacts readily with oxygen; a Korean study on how the two oils age in storage found it made up nearly half of perilla oil and barely a trace of sesame oil. It is the same quality that makes linseed oil, pressed from flax, useful for finishing wood. In fact, perilla oil pressed raw, without roasting, was long used in Korea not for eating at all but for oil lamps and for coating paper and cloth against water, a drying oil that hardens in the air. That is a wonderful property in a lamp and a frustrating one in a pantry.
Sesame oil is sturdier. Sesame seeds carry their own natural protectors, compounds called lignans, and roasting turns one of them into sesamol, an even stronger one. Together they slow the oil's decline considerably.
Researchers comparing the two oils under heat found perilla oil gave out in a fraction of the time sesame oil held. A good sesame oil in a cool, dark cupboard keeps its character for months. A good perilla oil left beside the stove can start to fade within weeks.
Korean cooks worked all of this out without a laboratory. My mother would not have said alpha-linolenic acid. She said perilla oil goes off, so you keep it cold and you buy only what you will use before the next market day. That was the entire lesson, delivered over a sink.
Sesame oil got the cupboard; perilla oil got the refrigerator door. The rule spread the way kitchen rules do, mother to daughter and neighbor to neighbor, until it stopped needing a reason. Ask a Korean grandmother why the perilla oil is in the fridge and she will look at you the way you might look at someone who asked why the milk is.
What changed was the bottle. The neighborhood mill still exists, but many Korean households now buy pressed oil from brands, and the best of them press once, at low temperature, and still bottle small. On an American shelf, that small bottle travels a long way from the roaster, which makes the old rule more useful, not less. The question is no longer which mill your mother used. It is how long ago the seeds were roasted, and how soon you will finish the bottle.
The bottles worth buying behave like a good mill that happens to ship. The pair I keep in my own kitchen come from Chung-O, which sprouts Korean sesame and perilla seed, washes it, roasts it low and slow, and presses it a single time → Chung-O sesame oil and Chung-O perilla oil. Neither is an aunt's soju bottle. But both are as close to it as anything that has to cross an ocean to reach you, and both come in bottles small enough to finish while they are still fresh, which is exactly the point.
I do not have a mill owner's ten thousand roasts behind me. What I have is a habit. The date printed on a bottle tells you how long it lasts unopened. It cannot tell you what happened after you opened it. For that there is the date I write on the cap, and my nose.
As It Transforms
The first day you open a fresh bottle of perilla oil, the smell is green before it is nutty, like crushed perilla leaves warmed in a pan, with a toasted edge underneath. Pour a teaspoon over a bowl of hot rice and you get it at once: soft, rounded, faintly grassy, gone from the tongue in a few seconds. Write the date on the cap with a marker. Cap it tight. Put it in the refrigerator door.
At one week it is unchanged, as long as it has lived in the cold and the dark. Taste it again on rice. Same green, same toast.
At three or four weeks, if it has stood beside the stove instead, you will notice the green going first. The aroma flattens. What was grassy now reads simply as oily, and the finish lingers a beat too long on the back of the tongue. The bottle in the fridge, opened the same day, still smells like the first morning.
By two or three months on a warm shelf, the change is no longer subtle. Unscrew the cap and smell before you pour. A rancid seed oil smells of old crayons or fresh paint, sometimes faintly of fish, and once you have smelled it, you will never mistake it again. That smell is the drying oil at work, the same chemistry as the lamp and the oiled paper. It is past saving at that point: every bowl you finish with it tastes slightly stale, and the bottle belongs in the trash, not the pan.
Sesame oil keeps a slower clock. Open it, cap it, keep it in a cool cupboard away from the stove, and at three months it still smells of toast. Do the same nose-first check before you pour. If the roast has turned flat and bitter, it is time.
That is the real reason for the small bottle. It is not thrift and it is not price. It is that an oil you finish before it turns tastes, on its last spoonful, the way it did on the first.
In Your Kitchen
Treat the two oils as two different shelves. Once opened, perilla oil goes in the refrigerator, cap tight. Cold slows its clock dramatically: Korean agricultural researchers found refrigerated perilla oil kept its quality many months longer than oil left at room temperature, so a bottle in the fridge stays good for a few months while one on the counter can fade within weeks. It may cloud slightly in the cold and clears again at room temperature.
Sesame oil can stay out, in a cool, dark cupboard away from the stove and the window, and keeps its best flavor for a few months after opening. If your kitchen runs hot, the refrigerator will not hurt sesame oil either, though it can turn cloudy.
The single most useful habit is the one my mother never needed: write the opening date on the cap. Few households finish a bottle of either oil in a month, and you do not have to. Just buy the smallest bottle you will use up within a season, not the largest one that looks like a bargain.
For the most Korean first use of a fresh bottle, brush perilla oil thinly over sheets of seaweed, sprinkle them with salt, and toast them in a dry pan for a few seconds a side until they crackle. Eaten warm with rice, that is the oil the way the mill meant it to be tasted.
Both oils have wandered well past the rice bowl lately. Korea is full of restaurants serving perilla oil buckwheat noodles, and what people actually line up for is less the noodles than the oil. Long a supporting player poured on at the end, perilla oil turns out to be fragrant enough to carry the whole bowl, and some noodle shops now press their own. Dessert has followed: cafés in Korea finish perilla seed ice cream with a thread of perilla oil, and in New York there is ice cream flavored with toasted sesame oil. At home it takes thirty seconds: a scoop of good vanilla ice cream, half a teaspoon of fresh perilla or sesame oil, a pinch of flaky salt, and a few crushed toasted seeds.
Small Bottles, Full Pantry
The Korean pantry is usually imagined as a place of patience: soybean paste that ages for years, jars that wait in the yard through a second summer. These two oils are the other half of that pantry, the shelf that does not wait. A good Korean kitchen holds both kinds of time at once, the slow jar and the quick bottle, and knows which is which. The jar teaches you to wait; the bottle teaches you to pay attention.
That is why the bottle is small. Buy it in the autumn, when the new seed comes in. Keep the green one cold. Finish it while it still smells like the first morning, and then go back for more.
FAQ
How do I store perilla oil, and how long does it keep? Perilla oil should be stored in the refrigerator, tightly capped, once it is opened; kept cold it holds its flavor for a few months, while on a warm counter it can fade within weeks. It oxidizes much faster than sesame oil because close to half of it is alpha-linolenic acid, a fatty acid that reacts readily with air. Keeping it cold and buying a bottle you will finish within a season matter more than any other storage trick. The single-pressed perilla oil Kim'C Market carries comes in a 160ml bottle sized for exactly that.
Does sesame oil go bad? Sesame oil does go bad, but slowly, because sesame contains natural protective compounds called lignans, and roasting adds another, sesamol. Kept capped in a cool, dark cupboard away from the stove, it holds its flavor for several months after opening. Rancid sesame oil smells flat, bitter, or like old paint instead of toast. If it smells wrong, it will taste wrong.
How can I tell if perilla oil has gone rancid? Perilla oil has gone rancid when its fresh, grassy aroma is replaced by a smell like crayons, paint, or fish oil. Smell the open bottle before you pour; the nose catches it before the tongue does. Once it smells that way, the oil is past its best and should be replaced, since it makes everything it touches taste stale. Fresh perilla oil should smell green and nutty.
Why is Korean sesame oil sold in such small bottles? Korean sesame and perilla oils are sold in small bottles because they are pressed from roasted seed and lose their aroma once opened, and perilla oil in particular oxidizes quickly. Korean households have long bought them in small amounts from the neighborhood mill and used them up fast. Unlike olive oil, they are finishing and seasoning oils used by the spoonful, so a small bottle lasts a household weeks or months.
Which should I buy first, sesame oil or perilla oil? Sesame oil is the easier first bottle, because its toasty flavor is more familiar and it keeps for months in a cool cupboard. Perilla oil is the one to add next, in the smallest bottle you can find, kept in the refrigerator door from the day you open it. Try both the same way, a teaspoon over hot rice with a pinch of salt, and the difference is clear in one bite. Most Korean kitchens keep one of each.