The Goodall household is well-trained. Compostable products get put on the compost heap. Plastic bottles end up in the recycling bin. Where should Innocent’s new smoothie bottles made from bio-degradable corn starch go? Surprisingly, the answer is into landfill. Innocent, the company with one of the purest brands in the UK, has made a mistake. For the last year it has used a new material called PLA for one of its ranges of drinks. It admitted last week that it would cease to use this bio-plastic later this year. But on its website it was still making some surprising claims. It says that the bottles made from this bio-plastic break down in garden compost heaps. They will not. PLA needs to be heated for several days to temperatures far greater than those in a domestic compost bin before it begins to rot. The bottles would break down in a commercial composter, but very few local authorities operate one of these plants. Innocent’s ethical consumers are going to find a large number of plastic bottles at the bottom of their compost heap next spring.

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The company says that in households without compost bins the bottles should be recycled along with other plastics. Unfortunately, this is another mistake. Recycling companies need to separate the different types of plastics so that reprocessing companies can melt them down and recreate the original plastic for re-use. Innocent’s PLA bottle looks and feels like a conventional soft drink container made from a plastic called PET. An Innocent bottle dropped into the plastic recycling box at home will eventually be sorted into a batch with Coca-Cola bottles made from the ubiquitous PET. The PLA will contaminate the batch, and may result in the reprocessor being unable to sell the plastic. PLA comes from the US, and recycling companies there have persuaded the bottling industry not to use the corn-based material in order to maintain the purity of recycled PET.

Innocent has also mistakenly said that the new plastic is ‘carbon neutral’. The plastic manufacturer does indeed stress that its product has a small carbon footprint compared to a conventional oil-based plastic. NatureWorks, the company that makes PLA in the heart of the corn belt, buys all its electricity from wind farms. However the company certainly does not claim that the farms that grow corn avoid the use of fossil fuels. Growing corn needs large amounts of fossil fuel-based fertiliser. Farmers use diesel fuel to run their tractors and ship the grain to the factory. Greenhouse gas emissions from producing corn are substantial. Innocent didn’t look carefully enough at the manufacturer’s slightly ambiguous claims on this issue. A boast that a product is ‘carbon neutral’ is rarely true and perhaps Innocent should have been much more sceptical before it made its own claims.

No one doubts Innocent’s genuine commitment to running its business to the highest ethical standards. It was one of the first companies to decide not to ship its ingredients by air. The company’s ethical sourcing principles are an example to others. 10% of its profits go back to charities in countries where its fruits come from. It has even tested the idea of putting a carbon label on one of its premium products. Its pristine brand image is one of the reasons why it can charge a king’s ransom for a litre of pulped fruit.

Using PLA for its bottles will have seemed an excellent way of keeping ahead of its competitors. Innovation is always risky, and no one can blame Innocent for its enthusiasm in experimenting with a new plastic being aggressively sold by its American manufacturer. It has only ever used PLA in a small fraction of its ever-expanding range of colourful drinks and the damage to its brand will be very limited. Nevertheless, it will make consumers a little bit more wary of trusting Innocent’s claims. A reputation for taking green issues seriously is increasingly valuable. Once lost, ethical credentials will be costly to rebuild.

There is another strange thing about Innocent’s use of PLA: it is made from genetically modified corn. None of us are privy to Innocent’s market research, but I would guess that its most devoted customers are anxious middle-class mums trying to get their children to eat more fruit. In my experience, people like this have a strong visceral distrust of GM foods. Why did Innocent decide to put its ethically sourced and highly nutritious foods in a container made from a substance its customers would strongly reject? And why did the company decide not to tell shoppers of its decision? For a business like Innocent, the green ethic has to run through everything it does and for once its high standards slipped.