Nearly three-quarters of the world's hazelnuts come from Turkey and the biggest buyer is Ferrero, maker of Nutella, the chocolate and hazelnut spread. But the nuts are picked mainly by migrants, including children, who work long hours for very low pay. What is Ferrero doing to ensure its products do not depend on child labour?
"When we say 'hazelnut', in my understanding it means misery: tough work, being a worker," says Mehmet Kelekci as he hauls a 35kg sack of freshly-picked nuts on to his back.
Around him, high on a Turkish mountainside, a family of fellow Kurdish migrant workers is moving slowly among the hazel trees. The father is using a wooden crook to shake the branches above his head; his wife and children bend double or squat as they reach down to pick the clusters of nuts in their pale green husks that cascade to the ground.
It's exhausting work, for about 10 hours a day, on slopes so steep that it's easy to lose your footing.
And two of the pickers, Mustafa and Mohammed, are working illegally. They're aged just 12 and 10, well below Turkey's minimum working age.
This is a typical scene in August, when the harvest is brought in along the Black Sea coast of Turkey, origin of 70% of the world's hazelnut supplies.
Most of the pickers are seasonal migrants from the poverty-stricken south and east of Turkey, mainly Kurds.
The official wage rate set by local authorities is 95 lira (£13; $16; €15) a day. Worked out on an hourly basis, this is less than the official Turkish minimum net wage of 2,020 lira a month for a 40 or 45-hour week.
But this family will receive even less - a maximum of 65 lira a day each, and possibly as little as 50 - after they've paid a 10% commission to the labour contractor who brings them, and the fare to and from their home town of Sanliurfa, and living expenses while they're away.
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Kazim Yaman, co-owner of the orchard, says he is against child labour. "They are making their children work like machines. They think: 'How many children, how much profit?'"
But he says most other farmers accept it - and that he has no option but to pay the children, because their parents insist that they work.
"I am trying not to make them work, but then they say they are leaving," he says. "The mother and father want them to work - and to be paid."
He adds: "This chain has to be broken."
But how? Turkey has about 400,000 family-owned hazelnut orchards. Most, like Kazim's, are tiny, just a few acres. Many growers, like him, don't know where their nuts end up.
At the far end of the often complex supply chain, are well-known Turkish and international confectionery brands including Ferrero - the Italian family-owned firm that manufactures Nutella, Ferrero Rocher and Kinder chocolates. Ferrero buys about a third of the entire Turkish crop. It has to. The amount of Nutella it makes each year weighs the same as the Empire State Building, about 365,000 tonnes.
On its website, Ferrero, which does not grow or trade nuts itself, says, "Traceability is essential to ensure the quality standards of production and products."
The company aims to make its hazelnuts 100% traceable by 2020. Currently, though, according to its latest report, to be published shortly, it has achieved only 39% traceability.
If you follow the buying chain, it's clear how far there is to go.
Enginay Akcay, based in Ordu, a Black Sea town dependent on hazelnuts, is one of thousands of small independent nut traders, known as manavs. Farmers deliver their produce in sacks and he pays them according to quality - the all-important weight ratio of shells to kernels - before selling on to cracking factories, or direct to exporters including Ferrero.
But he says that Ferrero doesn't ask him which particular farmers the nuts come from, or about working conditions on those farms.
"It has nothing to do with us, child labour. The control and the monitoring belongs to the state and the security forces."
Next up the chain are brokers such as Osman Cakmak. He buys from traders and sells to Ferrero and other exporters and manufacturers.
He also says Ferrero does not ask him which individual farmers grew the nuts he is selling.
"I buy, I sell. At that moment, it's impossible for the tons of hazelnuts to be monitored," he says.
As for Ferrero, he adds: "If they don't have their own farming value projects, it's not possible to know which producer they're coming from."
Ferrero's flagship Farming Values Programme, launched in Turkey in 2012, offers free training to hazelnut growers in more efficient cultivation techniques, to help them raise their incomes - though they remain free to sell their nuts to whomever they want.
On one of the model farms developed by Ferrero, company agronomist Gokhan Arikoglu shows how - with better pruning, irrigation, and pest control - a hazel tree can produce clusters of up to 21 nuts. On traditionally-run farms, four in a cluster is more typical.
Working in part with NGOs and other agencies, Ferrero also trains growers, farm labourers, labour contractors, traders, brokers and others in the community, such as village heads, to be aware of how the sector can be made more sustainable. That includes training on workers' rights, in particular on avoiding child labour. The company makes an effort to involve women, including women farmers, in its training programmes.
Ferrero says the programme has so far reached more than 42,000 farmers. That's about a 10th of the 400,000 in Turkey.
So how sure can the company be that its hazelnuts are not picked by children?
In a rare interview by one of the company's executives, Bamsi Akin, general manager of Ferrero Hazelnut Company in Turkey, says: "If we determine a product which is produced with unethical practices, we would not touch it. We are doing our role to improve social practices with trainings… But is the system completely clean? I think no-one can say that at this moment."
Asked about the trader and broker who told the BBC that Ferrero does not ask them about the exact source of nuts, Akin says: "We are not asking questions, but we have the tools to monitor from a different perspective… Before the season started, we have talked to them [the traders], and we have demonstrated our social practice requirements."
He says Ferrero has the names of the middlemen it buys from, and can provide a list, "apart from the trade secret side". But he adds: "I cannot guarantee the full names of the farmers."
As to whether the claims of traceability on the company's website are honest, he says: "Ferrero is always honest on the consumer side."
On the roadside below his orchard overlooking the Black Sea, farmer Kazim Yaman watches 12-year-old Mustafa empty another heavy sack of nuts.
He says regretfully: "The other day I saw the father put a sack, a very heavy sack, on the shoulders of the child. I said: 'What are you doing?' And he said: 'Let him get used to it.'"
Yaman says Ferrero invited him to participate in its Farming Values Programme, but he refused. Like many other growers, he belongs to an older generation - he's in his 60s - that is mistrustful of change.
He says: "The chain cannot be broken with the efforts of one or two people, but in time maybe, it will be broken, that chain."
Meanwhile, another family of Kurdish pickers is moving into the tiny wooden shack without electricity that will be home to six people - mother, grown-up son, two grown-up daughters and two smaller children - for the next month.
I ask the mother, Ayse, how often she eats chocolate with hazelnuts.
"I personally don't like it," she replies with a laugh. "The suffering and misery I have with this product, I don't want to see it."