TL:DR – Are Cadbury’s dairy milk bars sold in the UK but manufactured in Poland provably different in flavour to those manufactured in Birmingham? Yes, but…
Background: Around three years ago I conducted a scientific taste test of all caterpillar cakes which I published here in CasualUK to moderate interest. Keeping my eye out for similar chocolate-based questions of high priority, a friend recently linked me to a concerning claim about Cadbury’s Dairy Milk bars. So the theory goes, is that historically Cadbury’s made their chocolate in Bournville, Birmingham, but in 2017 moved some or all production to factories in Poland. Those bars are also sold in the UK alongside any from the Bournville site, but are (allegedly) inferior raising a deep ethical problem of essentially knock-off chocolate being sold as the real thing.
A formal comparison of the two types is made tantalisingly possible by identifying codes printed on the back of the bars. Scouring the shops in 2025 revealed no shortage of OBO bars (Bourneville) and a not-insignificant number of “OSK” bars. OSK allegedly means Skarbimierz in Poland and so with bars still being sold from Poland alongside Birmingham the question remains timely.
To properly assess this I conducted a blinded taste test of OBO vs. OSK bars to determine if they are indeed different and, if so, which is rated as superior.
Methods: There were two questions this study sought to answer.
1. Are OBO bars different in flavour to OSK bars?
2. If so, is one generally found to be more preferable than the other?
These objectives were explored via a single-blinded taste test. OBO and OSK dairy milk bars were purchased from shops in the UK (in Sheffield and London). The OBO bars came from a multipack but had the same segment design as the OSK bars. Expiry dates reasonably matched, with the one of each chosen at random having a BBE of 27/02/2026 and of 17/12/2025. The chocolate was prepared into half-segments and then blinded by a study team member who did not take part in the experiment. Each chocolate was assigned *two* numbers, being split evenly into four bowls that were labelled 1-4 (with 2 bowls having OBO and 2 having OSK).
Sixteen volunteers took part in the taste test. All participants were to make a total of four comparisons. Each comparison would use two samples from different bowls, ordered in such a fashion so that two of a volunteer’s comparisons would compare like with like (one instance of OBO vs. OBO and another of OSK vs. OSK), while the other two comparisons would compare the “different” chocolates. Participants were informed of this. The purpose of including known control trials was to mitigate placebo effects and make a volunteer feel more able to label a given comparison as being not-different. Participants were additionally reminded that the “different” chocolates may in fact also taste the same. The ordering of comparisons was randomised between subjects to balance on the first level the general order of “same” or “different” trials, and on the second level to balance if on the “different” trials participants tasted OBO first or OSK first.
After each comparison subjects first indicated on a response sheet if they believed the chocolates to taste the same or different via tickbox options. If they selected different they then gave a whole number between 1 and 10 to rate the flavour, with 1 being the “worst imaginable chocolate” and 10 being the “best imaginable chocolate”.
Statistical analysis examined the pattern of responses across each individual participant using binomial testing. In other words, the number of participants who “correctly” identified all four of their comparisons in terms of “same” or “different” was compared against the expected number of participants that would do this by chance alone, to see if this had happened more often than expected (and thus indicating that the chocolates are in fact different). Two different baseline “by-random-chance” probabilities were used to test against which worked on different assumptions about the manner in which participants may make decisions, one which may arguably underestimate how frequently the “correct” answers could be picked by chance and another which arguably overestimates it. More information is given about the calculation of these figures at the end of the study. In the event of a significant result posthoc analyses would then compare the chocolate ratings in the subgroup of participants who correctly differentiated between the two.
As a final, exploratory analysis, some participants were invited to eat additional dairy milk bars sourced from South Africa (coded OSA) and asked their opinion. These bars have an openly different recipe and so are expected to be different.
Results: Of the sixteen participants, six (37.5%) rated all four of their comparisons “correctly” with respect to their being “same” or “different” chocolates. A binomal test of this outcome compared against the liberal estimate of this being a 1-in-16 event indicated this was an inflated rate to highly statistically significant degree (p<0.001). It was also a significantly greater frequency compared against the more conservative estimate of it being a 1-in-6 event (p=0.038). The flavour ratings of these six individuals were consistent within themselves, i.e. each person rated the same chocolate as being preferable both times for each “different” comparison. However, neither chocolate was consistently preferred. A t-test of rating scores was non-significant (p=0.185). More pertinently, each chocolate type was rated as preferable by three members of this group of six.
The South African chocolate was called “shit”, “like that American crap”, and “it’s making me realise marking the Polish stuff a 2 was far too harsh”.
Conclusion: These results produce compelling evidence that Birmingham dairy milk is noticeably different in flavour to Polish dairy milk. Serious questions are therefore raised about the practice of selling these bars on UK shelves as the same product. While it appears that a little over half of people may not have sufficiently developed taste to reliably tell them apart, more discerning individuals do notice the difference at a rate far greater than chance. The fact these results were obtained to statistically significant degrees despite the small size of the study and in an intentionally over-challenging statistical design is suggestive of this being a particularly strong effect. Strikingly however, in this study different did not mean better; each bar enjoyed equal taste preference among the foodies of the group. Whether this absolves Cadbury’s of guilt in mixing products together is not for the authors of this work to comment on, although we encourage legal and philosophical experts to address this issue with haste.
The British public is urged to stay away from South African dairy milk.
Calculation of binomial test baselines: The first approach to calculating the probability of a person getting all four chocolate comparisons correct purely by random chance assumed that the decision making process could be equivalent to winning four coin flips in a row (a 1 in 16 event). However, this does not account for an expectation in participants that two comparisons are of the same chocolate and two of different chocolate. While subjects were not instructed to pick two and two in this way across their responses there was likely a motivation to pattern answers in this way. This is arguably equivalent to correctly calling four coin flips while knowing that two were heads and two were tails (a 1 in 6 event). Human psychology is complex and the true behaviour of volunteers will have been somewhere between these. Nonetheless both figures are used in analyses to explore either extreme.
by profheg_II
45 comments
Excellent work and a good report on such an important matter.
Thankyou, OP, for this highly significant advancement of scientific knowledge. Your igNobel prize is in the post.
My partner swears blind they’ve changed the bournville recipe, maybe this is the issue!
I’ve been wondering about this ever since I read a comment about it the other week. Thanks for this, much appreciated!
This is actual journalism. Good on you pal
So which is the chocolate bar to avoid? You’ve told us everything but which one…
A large part of the difference in taste will come from the milk used to form the crumb.
Source. Me 15 years as a chocolate R&D scientist
I have no idea who you are or where you’ve come from but I genuinely respect the absolute lack of casual_uk about this post.
Thank you for dropping the most important scientific paper of the year.
Ok great now please report on the thousand different varieties of KitKat Chunky.
At least 20 years ago (I was a child) I bought a dairy milk from the corner shop. It was disgusting. We posted it to Cadbury and got a letter back apologising, saying that bar was from Poland and shouldn’t have been on sale in the UK. I think they sent me a voucher for some random amount (£1.50 or so) with a suggestion I go out and carefully buy some Bourneville chocolate
Tackling the important issues, excellent work.
Cadbury should be held to account!
An even split on the taste between Polish & Brummagem bars is intruiging. Were any insights provided on what aspects of flavour were preferred between each batch? More sweetness, for instance? Less?
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If I might chime in with, Cadbury’s Dairy Milk Bars made in Ireland are a miles above the ones sold in the UK in terms of creaminess and quality.
Absolutely worlds apart.
This is beautiful OP. We used to have a “fun and humorous” conference event at my old institute (gah it was some sort of international effort borne out of the USA, I forget the name), and this would slot in well alongside the research on “do you get drunk quicker if you drink through a straw?” which is the only talk I can remember…
As a South African: yes on the chocolate. But all other sweeties are awesome. Fizzers, Super-C and Cream Caramels are my favourites!!
Cold hard evidence of a difference, now Mondelez must show their cards. What’s different in the manufacturing process. The public demands it.
I feel you should have had multiple OBO bars and multiple OSK bars, because maybe they could tell the difference but there is just a natural difference between any two bars.
https://awards.journalists.org/
Isn’t there also an Irish one? Anyway I read the old article on here about it and went to Morrisons to buy some. I bought the UK one (which I thought was Birmingham, not Sheffield) anyway I thought it was crap and actually chucked it because I didn’t want to waste calories on that junk. Whatever they put in it it’s not what they used to. I never buy Cadbury’s anymore.
Finally. We won’t be lied to anymore!
Are we saying that we have to go direct to the Cadbury factory for the better tasting chocolate?
Top tier post
Ain’t nobody got time for that. Where’s the Abstract bro?
No but seriously this is actually really interesting.
Seriously, take this to the press.
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Such chocolatey research is worthy of a Piece Prize.
This is brilliant.
Are these codes such as ‘OSK’ or ‘OBO’ printed on the product where the Use By Date is normally visible?
Great work! What was the average rating for each one?
Great work OP. This is what you call real journalism and tackling the issues of the everyday working person.
No more will Cadbury be able to lie to us
Careful, this sort of thing.
Brave and fearless reporting. Thank you.
I can tell this was a good study because I immediately skipped to the conclusion, then worked my way back up. As is tradition.
This is the sorta content I come to reddit for
This is fucking genius and it’s the type of research our overlords once used to do but now can’t be bothered. Well done chaps/ladies 🙂
I didn’t even know people thought this was a conspiracy this is common knowledge no? I no longer eat Cadbury as I noticed the change in taste before reading up on it. Don’t get me wrong it was never gourmet or anything but it tastes garbage now. I just assumed they changed the recipe all together.
I only buy Cadburys to support the local Brummie economy, it’s certainly not for the taste
This explains why it sometimes tastes like Cadburys.
I just went and had a look in the fridge (fight me) to check what mine was to see. I had noticed previously the chocolate wasn’t quite right but it wasn’t offensively wrong either and was close enough.
It’s `OWR`, which upon further investigation is apparently also from Poland.
Decided to take a gander at a couple of tubs of Heroes from various recent christmases (now repurposed as biscuit “tin”, misc shit storage, etc), which were either `OBO` or one was `ZCY`?
Someone needs to make a full repository or Cadbury location codes, what products they apply to, and where often they can be found.
Hi Op – have you tried a blind taste test between British and Irish Cadburys? Irish Cadburys has been sold in the UK for years – i think it’s where all the Wispa bars are made – the milk in Ireland is sweeter than the UK so you can notice the difference in how sweet the chocolate is
Very very interesting. I look forward to this being picked up by many news sites and you becoming semi famous like the a-z receipt guy.
However, can I just say before they write an article stealing your research, fuck the daily mail and fuck the sun.
>”It’s making me realise marking the Polish stuff a 2 was far too harsh”
Fucking hell, I’m reeling.
I appreciate the effort.
The key takeaway is that some people can distinguish between the two products above chance, which is interesting.
However, your results aren’t well presented. It would be nice to see the actual data (or even a summary table) to better understand the analysis and judge the strength of the conclusions.
I do genuinely think we need some sort of consumer protection laws against companies establishing a strong branded product and then gradually ‘boiling the frog’ with cheaper and cheaper ingredients until you pick one up one day and realize how crap it has become. If you’re going to do ingredient substitutions it has to be indistinguishable to the _original_ recipe not the already not-quite-as-good one you were selling six moths ago.
Also selling fewer items in the same or similar sized packaging as you were using for more of them less than five years ago, but that’s a rant for a different post.
This is true science. Chapeau!
Honey, wake up u/profheg_II has dropped their deep dive into the Cadbury chocolate Poland conspiracy
I demand a Parliamentary Enquiry.
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