SEOUL, South Korea — An hour before dawn, Kang Hye-jeong was already out cruising on her battery-run mobile refrigerator, briskly moving through alleys in Cheongdam-dong, a district of southern Seoul.
She parked her refrigerator and darted among apartments and office buildings, door to door and desk to desk, punching in building entry codes with ease as if she were another family member or colleague.
But to her loyal customers, Ms. Kang is simply known as a “yakult ajumma.”
Dressed in beige uniforms and quick with smiles and greetings, yakult ajummas have been fixtures in South Korea for decades. They sell yakult — a sweet, drinkable yogurt invented in Japan in the 1930s — from refrigerated carts. In many Korean communities, they have evolved from door-to-door saleswomen to surrogate mothers, daughters and aunts.
Ajumma is a Korean word often used affectionately to describe middle-aged women with children.
“I deliver yogurt but also cheerfulness and energy,” said Ms. Kang, 47, a yakult ajumma since 2012, who knows her customers’ orders by heart. “People, especially the elderly, feel good to see a cheerful and hardworking woman, and some of them eventually start buying from me.”
Ms. Kang was flagged down by a neighbor who bought yogurt but also gave her some of his rice cake. An old janitor greeted her warmly and gave her a cup of coffee in the chilly morning.
“She is always on time, with her smile and greeting,” said Lee Hae-sook, a wine-shop owner. “I buy yogurt from her and she helps me start my morning feeling good. It’s a win-win deal for both of us.”
Yakult ajummas have a long history in Korea.
In the early 1970s, the government provided farm subsidies to promote the country’s livestock industry. The growing cow business created a milk surplus because Koreans at the time had little appetite for dairy products. So Korea Yakult, in a joint venture with Yakult Honsha of Japan, introduced a sweet probiotic drink made from fermented milk, advertising the health benefits of “yusangyun,” or lactic acid bacteria, long before probiotic drinks became a part of the health food vernacular.
Yakult Honsha had already been using a network of women for home delivery in Japan, and the company’s Korean counterpart took to the idea. In 1971, a few dozen women looking for jobs to supplement their household income became the nation’s first yakult ajummas.
The work was hard. Lacking cold storage for fresh drinks, the women had to pull carts filled with ice to sell the yakult.
And buyers didn’t come readily. At first, the women were accused of selling “germs.”
The company launched an aggressive “good-for-gut health” ad campaign. Now there are customers in hillside shantytowns and gleaming apartment buildings, factories and Parliament.
There are roughly 11,000 yakult ajummas in South Korea, the nation’s largest female-only, home-delivery sales network. Half of them can be seen cruising around Seoul, riding their sleek mobile refrigerators called CoCos, short for “cold and cool.”
Yakult ajummas have been credited with helping to establish South Korea’s taste for dairy, and are so ubiquitous they have become minor pop culture celebrities. Their image has given rise to a song, and K-pop stars have even tried to do the job for a day.
Jeon Deuk-soon, 49, started working in Bongcheon-dong, a district in southwestern Seoul, as a yakult ajumma 17 years ago. The hilly neighborhood dotted with car-repair shops and sewing factories has been her beat ever since.
Ms. Jeon first carried her yakult in a push-and-pull trolley packed with blocks of ice to keep her drinks cool. When an alley got too narrow or steep, or when she faced steps, she switched to an insulated cooler bag slung over her shoulder.
“Imagine how I felt when I faced a three-block stretch of uphill climb,” Ms. Jeon said. “But I have always been constant, walking my streets whether it sweltered, snowed or rained.”
In 2015, as the proliferation of refrigerated trucks and convenience stores brought stiff competition to the market, Korea Yakult introduced the CoCo. The vehicle, which looks like a cross between a Segway and a golf cart, has helped rejuvenate sales by allowing the women to zoom up to five miles an hour on busy streets. Its 220-liter fridge carries cheese, cold-brew, fresh eggs and meat and even meal kits.
The yakult ajummas are part of the wave of women who joined the work force in large numbers in the 1970s. Often these women were driven by a fierce desire to finance their children’s education to elevate their family’s status.
They found work as street vendors, restaurant workers or whatever job was available outside their homes. In doing so, they were sometimes stereotyped as aggressive — willing, for example, to shove their way through crowds to find seats on the bus or subway after an exhausting day of work.
Ajummas were flouting traditional gender roles that expected women to be shy and focusing mainly on household work. And so they came to be nicknamed “a third sex.”
Today’s yakult ajummas are mostly in their 40s. They tend to work in the same neighborhood for their entire career, staying in the job for an average of 12.5 years. The job remains popular among women raising children who are attracted to the flexible hours and commission-based pay.
“When I started my gig, I had my grade-school daughter tag along on my round on Saturdays when she didn’t go to school,” Ms. Kang said.
Ms. Jeon, in Bongcheon-dong, said that she started the job after her husband’s bottled-water business failed, and that she has never taken more than a week off at a time. She said her income made selling yakult helped her raise two sons.
Over time, most yakult ajummas become cherished for more than their tiny grocery store on wheels.
Neighborhood women running late have called on them for help with child care and school bus pickups. They have been known to run errands and watch pets. And they are especially appreciated by their older customers.
“Old clients stop me to share all kinds of personal stories when I visit them,” Ms. Kang said. “I get impatient because I still have my route to cover. But I remember my own mom and listen to them, sometimes crying with them. In this modern world, they lack someone to talk to.”
Adult children living in distant cities will sometimes arrange for yakult ajummas to check on their aging parents and report back after making their delivery. In community programs coordinated with local governments, yakult ajummas bring free milk and yogurt and check on 30,000 seniors who live alone, often in semi-underground urban homes.
Such intimacy is part of what has kept the profession thriving in South Korea for half a century.
“I have raised six stepchildren and I don’t even know where they live now,” said Yang Hae-in, 91, who is one of Ms. Jeon’s customers. Ms. Jeon comes to see her every day, Ms. Yang said. The two held hands during a recent visit.
“She is like a daughter to me.”