I took a trip to the UK last week, and as an avid Coke Zero drinker, was surprised to find that my Coke Zero supposedly expired in March 2016 in most places I went.

Surprised, because in the US, diet sodas are typically dated 3-4 months from production, and actually do taste noticeably less sweet at that point (to the point that some brands of soda, including Coke Zero, are undrinkable for me if they're at the expiration date). March 2016, even assuming they were produced next door and stocked that day, was almost 6 months out, and considering about 75% of the sodas I found were that date (I did see some Jan and Dec, but almost all Mar) it sounds like they're dated at least six months out. But even the Dec dated sodas tasted fine (Which, if they were 3 months old, would start tasting off to me normally in the US).

Why is that? Does the UK have different regulations, or are there different formulas that explain it, or different storage, or ... something else? The base sweeteners were the same (Aspartame and Ace-K), though of course it's impossible to tell %s in the US so who knows if they're the same; and I think it all tasted differently there than in the US, so it's hard to say if there's more/less in there.

  • Are you certain the dates are the same function, the discrepancy could be explained if the US date was sell by and the European date was use by (or best before).
    – user23614
    Commented Oct 16, 2015 at 8:33
  • @user23614 Fairly certain. Soda isn't something that you would freeze or otherwise store in a preserved fashion, and I'm talking about single serving soda bottles here - so there should be minimal if any discrepancy between the two concepts, even if they are technically different. (And - the US date is a use by date, at least as far as my tastebuds are concerned...)
    – Joe M
    Commented Oct 16, 2015 at 14:29

2 Answers 2


First of all, sweeteners like Aspartame lose their sweetening property over time, as you have noticed yourself. This is very strongly tied to the pH level they are in.

US and UK/EU coke (or any country) is different, but you usually only notice the difference if you have them available for direct comparison. Coca Cola issues licenses and the plant managers produce the coke, but they do have a certain bandwidth they can operate in - usually to cater to local issues, like component availability, price, water quality. You can even taste differences in different batches of the same production plant, if you have them available for direct comparison and if you have a trained taste.

So, the deviation of the pH level in the different products results in different best before dates. The US coke pH level deviates more from the optimal level for Aspartame than the UK coke, so the US coke has a shorter best before date.

Whether the different pH level is on purpose or a necessity: no idea.

  • Hmm. The ingredients are identical excepting UK: Sodium Citrate instead of US: Potassium Citrate [a preservative/acidity regulator], and Potassium Benzoate US (none UK) (preservative). I could see that having some impact on pH. I don't see any evidence of this on the 'Net though - I can't find a consistent pH value for US, not to mention UK, Coke Zero (I've seen 3.18 - 3.5 values in various equally potentially valid sites).
    – Joe M
    Commented Oct 16, 2015 at 15:45
  • Either way - very possibly correct, would be better with some references (perhaps to the Aspartame wiki page which discusses the pH, as well as if you do have evidence of the pH).
    – Joe M
    Commented Oct 16, 2015 at 15:46

There are various possible reasons for different expiration dates in different markets:

  • As mentioned, formulation might be different.
  • Expected storage conditions (average temperature, or standard refrigerator temperatures with refrigerated goods) can be different regionally.
  • Criteria for when a product is still considered palatable and/or of prime quality can be different with different audiences.
  • Criteria when a product is considered unsafe or unfit for consumption can be differently defined by local law.
  • The costs/consequences of a mistake in estimating shelf life (leading to an unsatisfied or harmed customer) are dependent on local markets and regulations, so different risk factors will be accepted.
  • There could also be different legal standards on how a stated expiration date has to be scientifically proven.
  • That's an interesting list, but which one(s) specifically apply in this situation?
    – Joe M
    Commented Mar 27, 2017 at 14:07

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