Compostable packaging 'returns to nature'- but which bin does it go in?

What should you do with a compostable carton? You've had your takeaway, you're home, your stomach is satisfied, but your mind is a little confused: black bin, recycling bin or food waste bin?

Answering this apparently simple question led the team at the Climate Show to dive into the waste world.

First stop, BioPak, maker of compostable packaging with factories in Australia, America, the Middle East and mainland Europe.

At their warehouse, near Worcester, there are long aisles with racks of boxes, trays, cups and bowls reaching 10 metres high. Many of their plates and cartons are made from what's left over from sugar cane after the sugar itself has been extracted.

Their clear cups, which look like conventional plastic, come from corn starch. They're made from natural ingredients and the suggestion is that in the right conditions they go back to nature.

Sam Walker, BioPak's UK technical director, admits those conditions can be hard to create at home: "The challenge we have, particularly around home compostability, is people don't understand a well-maintained compost heap.

"It isn't just a pile of leaves in the corner or burying it underground.

"It needs aeration and to be turned and churned regularly. In those compost areas we find it does break down regularly."

But Danielle Purkiss, from University College London (UCL), carried out an experiment with hundreds of homes over a couple of years and found breakdown in the heaps was rare.

"We looked at some of these materials, especially the ones that have been certified as home compostable, and found that those materials didn't 'home compost' in people's own gardens as had been promised on the label," she says.

Some local authorities do offer food waste collection and this is the place to put your compostable cup.

Importantly, it can't go into the recycling bin as it can't be recycled alongside other plastic and can contaminate the whole bin.

But there is concern that even food waste collectors are sceptical about compostable packaging as they struggle to distinguish it from the regular plastic.

All these issues have led the sustainable online grocer Abel and Cole to dump compostables.

Their sustainability project manager, Hugo Lynch, tells Sky News: "We decided to remove [compostable packaging] from our range until the industry could provide resources to actually process this waste.

"We were quite shocked as we couldn't guarantee to our customers that the packaging would actually be processed in the way that we were telling them that it was."

But manufacturers such as BioPak insist compostable containers have an essential role in the food service sector, as it doesn't matter if they are dirty.

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Contaminated plastic almost always gets burned or buried, whereas food waste on compostable packaging actually helps it decompose.

"You go to any fast-food restaurant chain and look in that bin. There's cardboard, there's plastic, there's ketchup all over everything. And that's supposed to go to recycling. It doesn't, it gets incinerated," says BioPak's Sam Walker.

"The whole purpose of compostable packaging isn't about composting the cup. It's about composting the food that is in the cup."

And that's the takeaway emerging from this murky picture.

If you are sure it's compostable packaging, bin it with the food waste - if that's collected in your area - and in the black bin if it's not. Just not with the recyclables.