Roasted sesame on the air: inside the bangatgan, Korea's neighbourhood mill

You smell the shop before you can read its sign. Halfway down a market lane in eastern Seoul the air turns warm and toasted, and behind a sliding glass door a steel drum is turning over a gas flame while a woman sits on a plastic stool with an empty sack folded on her knee. She is not shopping. She is waiting for her own sesame seeds to come back to her as oil.

A mill that works on other people's ingredients

The shop is a bangatgan (방앗간), a neighbourhood mill, and its logic is the reverse of a grocery's. Customers arrive carrying the raw material — a sack of sesame from a relative's field, a clear plastic bag of dried red chillies, a basin of rice soaked overnight — and pay for the labour of turning it into something a kitchen can use. What goes home is chamgireum (참기름), toasted sesame oil; gochugaru (고춧가루), chilli flakes; or rice flour for tteok (떡), rice cakes.

Many mills also sell from their own stock, which is how a traveller without a sack gets in the door. Look for the word 기름 (gireum, oil) painted on the glass, or a shopfront labelled 떡 방앗간. Handwritten cardboard signs name the origin of the seeds: 국산 (guksan) means grown in Korea, and the gap in price between that and imported seed is wide enough that the two are kept in separate bins and pressed separately.

The drum, the press, and the green bottle

A pressing is short enough to watch from start to finish. The seeds are rinsed, tipped into a rotating drum, and roasted until the colour deepens and the smell reaches the street. Then they go, still hot, into a steel cylinder under a hydraulic press. The machine hums, a needle climbs on the gauge, and a thin amber thread starts to run from a spout into a kettle lined with filter cloth.

The oil is funnelled into green glass bottles of the shape soju comes in, capped by hand, and wiped down with a rag. What is left in the cylinder is a hard brown disc called kkaetmuk (깻묵), the pressed cake, which gardeners take away for fertiliser and anglers for bait. Regulars stay on the stool through all of it. The old explanation, usually offered with a laugh, is that you watch so you know the oil in the bottle came from the seeds in your sack.

Two oils, and the one visitors overlook

Sesame oil is the one most people already know: a finishing oil, added at the end to namul (나물), seasoned vegetables, or stirred into bibimbap (비빔밥). Next to it on the shelf, in the same green bottle, is deulgireum (들기름), pressed from perilla seed. Perilla is the plant whose leaf, kkaennip (깻잎), often arrives in the lettuce basket at a grill restaurant. Its oil is grassier and earthier, and Korean home cooks use it where they want depth rather than perfume — brushed on sheets of gim (김), dried laver, before toasting, or, in some households, as the oil in which seaweed soup, miyeok-guk (미역국), begins.

Some mills also press perilla without roasting it. The result, saeng-deulgireum (생들기름), is paler and milder and tends to cost more. Shopkeepers will usually tell you, unprompted, that perilla oil belongs in the refrigerator and should be used up sooner, while sesame oil keeps in a dark cupboard.

A queue that follows the calendar

The mill's year can be read from the pavement. In the days before Seollal (설날), the lunar new year, steam pours out of the door and long white cylinders of garaetteok (가래떡) are pushed out of a machine into cold water, cut to length, and laid in trays; sliced thin, they become tteokguk (떡국), the rice-cake soup the holiday is built around. Before Chuseok (추석), the autumn harvest holiday, the order is rice flour for songpyeon (송편), the half-moon cakes families shape at home. In a busy week the line outside may be made of basins rather than people, each one holding somebody's soaked rice and their place.

Late summer into autumn belongs to chillies. Households bring sacks of sun-dried peppers to be ground ahead of gimjang (김장), the yearly kimchi-making, and ask for a coarse grind for kimchi or a fine one for gochujang (고추장), chilli paste. The air inside stings, and the queue tends to sneeze together. In the hot months the grinders turn to misutgaru (미숫가루), a powder of roasted grains that is stirred into cold water or milk.

Where to find one in Seoul

The densest cluster is at Gyeongdong Market (경동시장), which spreads between Jegi-dong Station (제기동역) on Line 1 and Cheongnyangni Station (청량리역). It is known first for dried herbs and roots, but its lanes also hold a run of oil shops with presses working near the door, and the smell changes every few metres from sesame to perilla to chilli. On the other side of the city, Mangwon Market (망원시장), a short walk from Mangwon Station (망원역) on Line 6, has oil and rice-cake shops among its fried-food stalls, and is easier to fold into an afternoon around Hongdae (홍대).

Smaller mills sit outside markets altogether, on the ground floor of low brick buildings in residential streets, often with a few sacks stacked by the door and a television on inside. These are working shops, not set up for visitors, which is the reason to go. Stand at the threshold, nod to the owner, and keep out of the path between a regular and their seeds.

Buying a bottle and getting it home

Go on a weekday morning, when the presses are running and the owner has time to answer a question. The week before either big holiday is the most vivid time to look and the worst time to buy. Market shops keep their own rest days, and those shift, so check the market's notice board or the official Seoul tourism site before crossing town. Prices depend on bottle size and on where the seed was grown, and are usually written on the cardboard signs; confirm at the counter, and carry some cash in case a card is waved away.

To buy sesame oil, the sentence is short. Chamgireum han byeong juseyo: one bottle of sesame oil, please.

참기름 한 병 주세요.

The mistake to avoid is trusting the bottle. Sesame and perilla oil are sold in identical green glass, often with a handwritten label or none, and the two do not behave the same way in a recipe. Learn the first syllable of each — 참 for sesame, 들 for perilla — and say it back to the shopkeeper before paying. Ask for the bottle to be wrapped, pack it upright in checked luggage, and confirm your airline's rules on liquids and your home country's rules on bringing in food before you fly. Buy the small size of perilla. It will be finished, or past its best, sooner than you expect.