Skip to content

Potato logic: News media repeat zombie statistics on food wastage

January 10, 2013

Major UK news outlets gleefully announced today that 30% of the UK vegetable crop is ‘never harvested’ and half of the world’s food is ‘thrown away’. A major initiative by Waitrose to reduce food waste has been strangely inverted by statistical spin-doctors and journalists into a supermarket bashing story! Real levels of harvesting wastage are probably less than 10%, and difficult to avoid.

This blog reveals how respected news organisations across the UK have fallen for the oldest trick in the book. In today’s news hungry environment, when you need to get noticed, the best way is to get some spurious stats and then exaggerate, exaggerate, exaggerate. And this is what the UK Institute of Mechanical Engineers (IMechE) did today.

You have to hand it to the IMechE press office – they got the mainstream media to swallow the story hook, line and sinker!


This blog is about using evidence and facts to determine government policy and execute effective change initiatives. I am a sceptic. I am not a negative thinker. I just do not accept statements as facts without supporting evidence. We must be scientists – we should not accept the authority of an author at face value…

Let’s look at the story…

A headline news article on the front page of the BBC news website said:

“Half of all food is thrown away … (and) up to 30% of vegetables in the UK were not harvested because of their physical appearance.”
Source: (accessed at January 10, 2013, 09:10am)

The source is a report published today by the UK Institute of Mechanical Engineers.

“Half” is not the same as “Up to half”

Headlines are typically not written by the journalist who wrote the article. A sub-editor will scan the journalist’s text. You will often see inconsistencies and exaggerations between a headline and the detail of the text – and this case is no different.

The text in the body of the BBC article actually says:

As much as half of the world’s food, amounting to two billion tonnes worth, ends up being thrown away.”

OK – so it is “as much as half” not “half”. We don’t know how much less than 50%.

49% perhaps? One percent perhaps?

Are “30%” of UK vegetables never harvested?

No. Let’s go and check the detailed report. It does indeed claim that:

“up to 30% of the UK vegetable crop is never harvested.”
Source: Global Food. Waste not, want not. London: Inst. of Mechanical Eng., 2013, p.18

Wow. That sounds very worrying. Let’s look at the evidence on which the report’s (anonymous) author is basing this disturbing statement.

The source given on page 31 is:

“War on Waste, Solanum in collaboration with Waitrose”

Well, this is a strange reference. There is no date or indication of the author, format of the report, its location or availability. This aroused my suspicions…

Digging around the Internet for potato stats

In fact, I had to do quite a lot of searching to check out this ‘fact’.

The name of the source is interesting. Remember what the subject of today’s blog is? Yes – the humble potato, solanum tuberosum.

It turns out that Simon Bowen (an expert potato nematologist)1, the technical director of an organisation called Solanum UK (which is part of the Produce World Group2) gave a talk at the World Potato Congress in Edinburgh in May 2012.3

Farmer’s Guardian online reported on Simon’s talk as follows:

“Simon Bowen, technical director at Solanum UK and Alan Wilson, technical manager for agronomy at Waitrose, discussed their joint ‘War on Waste’ project. … The standards of the supermarket and its growers are among the best in the country … in 2008 (the) average loss from field to supermarket shelf (was) 42 per cent, although some of those rejected potatoes would be sold to secondary lower value markets. A strategic approach identifying and addressing problems had since been implemented. Its aim was to reduce waste to 33 per cent by 2011. Dr Bowen said, that in a difficult year, this target was missed by just 3 per cent.”
Source: Farmer’s Guardian Website, June 6, 2012

So, Waitrose has reduced its waste to 33% plus 3% = 36%. It looks like the report’s authors made an arithmetical error in coming to a 30% figure by subtracting 3% instead…

OK – so are 36% of potatoes in the UK are not harvested by Waitrose suppliers?


Farmer’s Guardian (which I am coming to respect more and more as I delve into these stats!) provides a breakdown of the survey’s findings:

(The more nerdy of you out there may have fired up Excel to check my arithmetic, and may be wondering why the above numbers don’t add to 42% – this is, I shall assume, simply due to presentational rounding errors.5)

So only 12% + 1% = 13% appear to be ‘lost’ by grading losses or supermarket quality control…

Wait a minute!

Of the 12%:

some … would be sold to secondary lower value markets“.

So the true level of loss due to what a commentator on Radio 4 today called ‘wonky vegetables’4 is less than 13%. Presumably what remains are tubers that are so misshapen that they cannot be readily prepared for consumption…

It gets worse…

This is a survey for Waitrose, who (as Farmer’s Guardian correctly states) have probably the most exacting of quality standards of any major UK supermarket. I would expect that more ‘down-scale’ supermarkets would have lower scales of loss.

Let’s check out the dates…

These figures are from 2008! Waitrose (that evil, capitalist supermarket) has since instituted programme called ‘War on Waste’ which has resulted in potato losses reducing from 42% to just 36%. The 13% breakdown is more than four years old. We do not have an updated current breakdown of the harvested food that is ‘thrown away’, but it is somewhere between 7% and 13%.

To summarise:

Four years ago, a survey of twenty suppliers of potatoes showed that less than 13% were not accepted by an upmarket UK supermarket. Some of this 13% were sold elsewhere. Since then, a project initiated by the supermarket has reduced overall wastage by 6%.

This statement has been expanded and extrapolated out at each step of the process from Dr. Simon Bowen’s original verbal report into the news release today that 30% of UK vegetables remain unharvested. The authors have extrapolated various other statistics which have resulted in a misstatement by the news media that half of all food is thrown away.

I fully expect the 50% and 30% numbers to now become zombie statistics,6 being repeated for many years to come as unassailable facts.

Welcome to the modern world of statistical spin-doctors and journalism!



Comment below…



1 Dr. Simon Bowen

2 Produce World

3 WPC 2012

4 BBC Radio 4 News January 10, 2013 11:00am

See nerdy paper here

6 Zombie Stats

© Brian Wernham 2013 CC BY-NC-ND

  1. JTM permalink

    Tristram Stuart’s 2009 book Waste: Uncovering the Global Food Scandal comes up with a similar 13%(ish and by kCal rather than weight) figure based on FAO data (not the most reliable source – but often all there is). He calculates that, of a total global edible food harvest of 4,600 kCal per person per day, only 2,000 kCal are consumed. 1,700 are fed to animals, yielding just 400 in return; 600 are lost between field and food industry (your 13%ish) and 800 lost in distribution, retail, catering and households (bear in mind that Stuart’s figures are global and include regions where in-field and post harvest losses are higher than in the UK).

    Add the field loss to the distribution loss and Stuart ends up with about 30%. (Personally I’m not counting the kCal fed to animals as waste… as such arguably I should use 3300 kCal as the total available per person per day, but I’ll leave that for others think about.)

    In the end I think there is very little reliable data out there to allow much confidence in any of these assertions. However, whatever the numbers, food waste is clearly an issue that needs tackling. The lack of data runs both ways – those arguing we need to double food production by 2050 in order to meet population growth and the demands dietary changes (more meat and dairy) take just as much of a punt on the figures.

    In truth we probably need to cut waste and up production (though how we do the latter is moot), but critically we need to address issues that effect access to food…

  2. Hi Brian. Why have you excluded the 6% “field loss” and the 22% “post washing loss” when you calculate that 13% were rejected by the supermarket?

    My reading of the press release from the Potato Council ( is that 6% were rejected in the field, 12% at an initial grading, 22% at a second grading after the potatoes had been washed. A final 1% were then rejected by the supermarket when the potatoes finally reached them (with a further 5% lost in storage at some point along the chain).

    While the supermarket only directly rejected 1%, I understand that the 6%, 12% and 22% filterings will all have happened because the potatoes didn’t meet quality criteria defined by the supermarket. So the supermarket is responsible for all these losses in the sense that it defines the criteria by which they’re rejected, even if it wasn’t supermarket employees who did the rejecting.

    Of course, your points about the “as much as half” and “up to 30%” still hold, as do the questions about dates & the impact of subsequent improvements.

    There’s also the question as to how many potatoes would have been rejected by any criteria (e.g. were diseased) rather than just by the exacting standards of Waitrose. (BTW I don’t think the big 4 supermarkets are much, if any, less exacting than Waitrose here — quality of fresh produce is one of the things which sticks in consumers’ minds, so they all police it carefully.)

    To put this into context, much of the fruit that goes into Innocent Drinks’ smoothies is seconds, i.e. has been rejected as not meeting the criteria set by the supermarkets. Yet these are a premium product! The rejection criteria often have little to do with taste and nutritional quality. But that only creates waste if there’s no secondary market for the produce (although it reduces the farmer’s income). So the numbers are meaningless without knowing the size of this secondary market.

    And, according to the Potato Council release, some potatoes were rejected due to “damage”, presumably as the potatoes were lifted and processed. That’s due to the farmer’s and processor’s actions rather than the supermarkets…

    And finally, remember that in the developed world more food is probably wasted after it’s sold by the supermarket than before it gets to the supermarket. Part of this is due to the way food is packaged (making it easier to buy a kilo of potatoes than the 600g you really need; putting needlessly strict “use by” dates on produce; etc). So that’s another unquantified element of the total waste.


    • Graham,

      Thanks for the detailed review of my blog – it is good to take a sceptical view of my sceptical view!

      I am not a potato expert. In fact I am a blogger specialising in evidence based agile government…

      I interpreted the 6% field loss to be potatoes not harvested because they were missed by the harvesting process, not because a supermarket had wickedly decided not to accept a slightly odd shaped tuber.

      If I could invent a potato digging machine that would consistently harvest 100% of potatoes (in any weather, soggy soil or dray and as hard as rock) I am sure that I would be a rich man!

      Could the 22% post washing loss refer to throwing away tubers that were damaged during harvesting, or were found to be diseased? Throwing these away would make good sense wouldn’t it?

      You are right that a proportion of the 13% not suited to Waitrose (and it is just the one supermarket’s stats that have been twisted in the report) are sold onto other buyers – local markets and processed food manufacturers (for the yummy mashed potato topping of shepherd’s pie maybe?).

      Of course everybody could do more to reduce waste – but my point is that we need accurate and up to date stats if we are to target waste, no headline grabbing numbers.

      Also it seems unfair to poor old Waitrose (!) that their transparency over their waste reduction initiative has resulted in a supermarket bashing PR exercise by the IMechE in their report (and adopted with such relish but the chattering journalist classes that cut and paste so readily from press releases…)

      This blog has created quite a media storm – the blog stats are overwhelming – I thought only a few hundred people at most would read it.



      • Yes, food waste is a big issue for many people. (I heard the story reported as a “we must reduce waste” one, not as an “aren’t the supermarkets horrible one”.) It overlaps with my interest in agile development through the stuff I’m doing with Five Mile Food. (

        Re. the 6%, the potato council site says “Some 6 per cent were failed at field level before or soon after lifting began, due to size, quality or bruising problems”. So I don’t read that as failure to harvest: it’s a decision to reject what’s been harvested (partly due to problems of harvesting — bruising — partly due to quality standards — size & quality).

        It says that the 22% loss is due to greens, damage & skin disease. It doesn’t say how bad the damage has to be to lead to rejection — potatoes with minor damage could well be usable. Again, the standards are set by the supermarket, which sets them very tightly, almost certainly leading to rejection of some produce that’s actually usable.

        On the bigger picture, there’s little doubt that food waste is a big issue, for the UK & globally. It’s not solely the supermarkets which are to blame — a system has co-evolved amongst the supermarkets, producers, processors, consumers and government. Until we address that whole system, things won’t get much better. And yes, better statistics are part of understanding that bigger system.


  3. Update:

    ‏@david_navigator says “@BrianUkulele Though I don’t think you don’t mention in your blog – esp Annex 4″

    @BrianUkulele says “Yes – the main reference is a 2011 report using information from the FAO Statistical Yearbook 2009 on 2007 production! ”


    … and “50%” is not a statistic in that report anyhow!

  4. Hang about here!

    It must be pretty obvious that UK and Western farming methods are pretty efficient in terms of “field to supermarket shelf” losses, perhaps it’s only ten per cent (for sake of argument, surely there is an irreducible minimum). So hooray for UK farmers and food packagers, retailers.

    But the “shelf to plate” losses incurred by consumers are pretty high (maybe 20 per cent, for sake of argument), total 30%. They are paying for the food and are perfectly entitled to chuck it in the bin after a week.

    I think what the IME were talking about mainly (because they see juicy contracts here, fair play to them) is farming methods in developing countries (irrigation, infrastructure, storage, transport), which are colossally inefficient (probably their governments’ fault rather than the farmers’ faults, we don’t know).

    If they say that half of food grown in these countries is either not harvested, spoiled in transit etc, then I wouldn’t be at all surprised. But whatever the percentage is, surely it is higher than in the West? i.e. more than 30%.

  5. Update: BBC Radio 4 programme “More or Less” just broadcast a debunking that supports my case above. It should be available to listen to until 2014:

    (Listen from 15 seconds)

Trackbacks & Pingbacks

  1. Wasted Food -- Jonathan Bloom on food waste and how it can be avoided

Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s

%d bloggers like this: