By Anthony Reuben
Business reporter, BBC News
More than a million unopened pots of yogurt and yogurt drinks are thrown away in the UK every day - that's 484 million a year, according to recent research.
How on earth did they find that out?
Well, it was a lot of work.
Rubbish was collected on the usual collection day from 2,138 households in nine areas in England and Wales, all of which had consented to have their refuse analysed.
A team then divided it into food and non-food waste and disposed of the latter.
Any recognisable food was then painstakingly catalogued while anything unrecognisable was classified in the wonderfully-named category of "composite gunge".
"What they wrote down was a huge amount of detail for each item so, for example, if it was a cherry yogurt from Marks and Spencer they would write all that down," says Barbara Leach, who is evaluation manager at Wrap, a government-sponsored group that encourages companies and individuals to recycle more, which commissioned the research.
Wasted food was then weighed without its packaging so that the people doing the analysis could calculate how much it would have cost.
I can tell you that it's the tip of the iceberg because we've just received a draft report into food that's thrown down the sink
Obviously, the research was not just into wasted yogurt.
Wrap came up with figures for all sorts of wasted food.
For example, 4.4 million whole apples and 1.2 million sausages are thrown away each day.
The overall research, including analysis of the figures and interviewing the households involved, cost £426,000.
"It is obviously a very significant investment but the scale of the issue on food waste and the urgency of addressing it, we believed, warranted it," says Barbara Leach.
"It's not something we want to do again quickly though."
The work was carried out by a team of 12 people travelling around the country over a five-week period to sort through people's rubbish.
"Logistically it was very complicated because we had to get 12 people moved around the countryside and arriving on specific days to collect rubbish from a specific number of households who had given their consent," says Sarah Knapp who, with her father Barrie, founded WastesWork, the company that did the waste-sorting.
It is Barrie who looks after the teams in the field, and he says that people are queuing up to do this sort of work.
"I have a lot of people calling me up to ask if there is work available," he says.
"They get paid quite well and they enjoy doing the work. They're quite happy to put up with nasty smells and mess and all the things that people tend to throw away and they're perfectly prepared to come back for more."
His daughter says there is another attraction to the work.
The team spent five weeks going through people's rubbish
"Most of the people who work for us are environmentally-aware type people who want to work with a good cause like recycling."
Given the work that Barrie Knapp does, there is not much in the report that surprises him.
"It probably came out pretty much as I would have expected, because I'm there on the ground floor with my hands in the muck up to my elbows four days out of every seven," he says.
And seeing all the waste has certainly influenced his behaviour at home.
"We recycle absolutely everything at home," he says.
"There's not much going into our dustbin apart from packaging which can't be recycled."
So, the amount of work all this took is clearly mind-boggling, but do we believe the results?
In the 12 months to 14 June 2008, 5,026 million pots of yogurt and yogurt drinks were bought in Britain, according to the market research company Nielsen, which is a relevant period given that the rubbish was searched between September and November 2007.
Wrap found that 484 million pots a year are thrown away in the UK.
Adjusting the Britain figure to include Northern Ireland, it turns out that about 9.4% of yogurt pots bought are thrown away unopened.
Does that ring true with your own experience?
Even if the figure sounds in the right ballpark, there are a few flaws in the research.
First of all, the households surveyed were in England and Wales, while the overall figures claimed to cover the whole of the UK.
Secondly, all of the households covered lived in houses because the way that rubbish is mixed in flats makes them difficult to cover.
Wrap will be doing some research in Scotland soon that it hopes will include flats, but it believes that the results will not be dramatically different.
"I would suspect that people who live in flats will be no different from anybody else and they'll be wasting a significant amount of food," Barbara Leach says.
She was surprised at how little difference there was between the amounts thrown away by different groups.
"Some groups are worse than others, but even people who lived through the war and complain about 'the young people of today', actually we found that they were throwing out food as well," she says.
There may also be seasonal effects. The research was carried out between September and November, but it may be that in the height of summer, for example, people buy and throw away more yogurt than they do in the autumn.
The sample size of 2,138 households is certainly a robust number and the report's authors are pretty certain their results are correct.
Almost one in ten yogurts bought is thrown away unopened
"We can be 95% confident that the headline findings of this research are within 2.1% of the results that would have been obtained had everyone in England and Wales had their waste analysed," the report says.
"It seems as though it's been an interesting effort and fairly well done," says Sheila Bird, vice-president of the Royal Statistical Society.
"But I'd be very surprised if it was that accurate - that is very precise," she adds.
She says it is enormously difficult to pick a sample of households, even a large sample, that is so accurately representative of the whole population.
'Tip of the iceberg'
The research only covers unopened yogurt pots thrown away by households at home.
There is no consideration of unused pots thrown away by shops, restaurants and cafes, and there is another category that gets under the radar, so the actual figure for wasted yogurt is probably much higher.
"I can tell you that it's the tip of the iceberg because we've just received a draft report into food that's thrown down the sink," Barbara Leach says.
"I can tell you that there's a significant amount of yogurt that's thrown down the sink that hasn't been counted in this report."