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According to the Coca-Cola website and every label I read, Coca-Cola Zero Sugar is a mixture of organic compounds:

CARBONATED WATER (OC(OH)₂), CARAMEL COLOR (Various sugars), PHOSPHORIC ACID (H₃PO₄) , ASPARTAME (C₁₄H₁₈N₂O₅), POTASSIUM BENZOATE (C₇H₅KO₂), NATURAL FLAVORS, POTASSIUM CITRATE (C₆H₅K₃O₇), ACESULFAME POTASSIUM (C₄H₄KNO₄S), CAFFEINE (C₈H₁₀N₄O₂).

The label also says 40 mg sodium. There's a perceptible salty taste in the beverage, which suggests to me that something activates the taste receptors for saltiness, but a potassium cation can do that just fine.

There is no sodium in any of those molecules. That means "Natural Flavors" must contain the sodium... but in what form? The essential oils in things like OpenCola seem to all be hydrocarbons without sodium. And if it's plain old NaCl table salt, why wouldn't they just list it as "salt"?

Where's the sodium in Coke coming from?

EDIT: The discussion has centered around the sodium content of "still" drinking water; what about the process of carbonating the water? Some processes add a sodium carbonate to the solution; could that be the source, contained in the ingredients list as "carbonated water"?

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    $\begingroup$ You forgot water, it's not like they're using twice distilled. $\endgroup$ – Mithoron Feb 2 at 18:28
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    $\begingroup$ They probably are; it would be the only way to control flavor. Dasani gets filtration and purification and is then re-flavored. $\endgroup$ – Rob Perkins Feb 3 at 2:22
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    $\begingroup$ The claimed sodium content is far too uniform to explain this by saying it's in the water. Dasani is bottled by Coca Cola bottlers. $\endgroup$ – Rob Perkins Feb 3 at 3:40
  • $\begingroup$ I keep forgetting to mention that Dasani's sodium content is reported as "0", meaning in the U.S., between 0 and 4 mg. No; not twice distilled, but yes; reverse osmosis and other filtration are almost certainly in use. $\endgroup$ – Rob Perkins Feb 5 at 2:34
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    $\begingroup$ And, I'm made thoughtful by the idea that I considered ingredients but not process while thinking about it. See my edit in the question: Could the sodium come from the carbonization process? $\endgroup$ – Rob Perkins Feb 5 at 2:42
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Basically, the Sodium could come from any or all of the ingredients used to manufacture Coca Cola. The ingredients list is based on the raw-materials used in the product, but these ingredients are not necessarily pure, even if they are Food Grade. As an example: The Phosphoric acid used is probably a 75% H3PO4, a common commodity in the industry, but the remaining 25% is not pure water. It may contain a number of impurities and by-products, such as Sodium, but as long as they are considered harmless they will not be listed anywhere.

The Sodium-content in the Cola, is on the other hand based on an actual analysis of the final product (at some point during product development).

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  • $\begingroup$ So if I'm understanding it correctly I'm considering the fact of food grade ingredients containing other ingredients that might be sodium, implying that the FDA permits impurities that add up to real nutrient content, measured separately from a different analytical method. That's decent but the sodium content is itself too uniform on that label for every Coca-cola produces carbonated beverage, worldwide. That implies some kind of regulated process inserts or balances it. $\endgroup$ – Rob Perkins Feb 5 at 22:32
  • $\begingroup$ I have no inside information about the production of Coca Cola, but I imagine that the company has very strict specifications for the ingredients they use, above and beyond what FDA requires. Also, at least in my region of the world, Cola is made from concentrate that is diluted at a local brewery. All in all, this results in a very uniform product. But furthermore, Sodium is not analyzed and specified (on the label) for each batch. It is stated as a “typical value” and it is only required that it is monitored as part of the company’s own quality control. $\endgroup$ – FrankS Feb 6 at 6:16
  • $\begingroup$ Both answers are correct; it's "water and other stuff", but this one said so specifically. I think what I ran into is a difference in analytical methods (in the Coke, not the answers). A lesson not to expect purity from real life. :-) Thank you all for contributing. $\endgroup$ – Rob Perkins Feb 11 at 22:51
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Two sources: water and natural flavors

According to the Wisconsin department of healt natural sodium levels in water is $\pu{40-60 mg/L}$ meaning a $\pu{20 fl oz (\! 591 mL)}$ Coke has about $\pu{25 mg}$ of sodium from water. Thus the other $\pu{50 mg}$ of sodium must come from natural flavors. This makes sense since Coca-Cola uses plant products like coca leaves which would naturally add sodium to the carbonated sugar water.

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    $\begingroup$ coca leaves, are you sure, generally to use these these is illegal. $\endgroup$ – porphyrin Feb 2 at 21:55
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    $\begingroup$ @porphyrin Yes they do use coca leaves still, though by the time Coca Cola receives them the cocaine is not present. en.wikipedia.org/wiki/Coca#Legal_status $\endgroup$ – A.K. Feb 2 at 22:01
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    $\begingroup$ @RobPerkins Taste generally isn't uniform and water has like smallest effect on it. They even use different receipts in different countries. $\endgroup$ – Mithoron Feb 3 at 2:30
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    $\begingroup$ Uhm, you probably meant "the other 20 mg of sodium". I didn't realize coke still contained extract from coke leaves, but what guarantee that this is the source of the sodium? Fascinating, but seems like guesswork. $\endgroup$ – Buck Thorn Feb 3 at 10:47
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    $\begingroup$ The most important fact here is that potable domestic water supplies can contains 40mg/L of sodium. This puts the presence in Coke in perspective and suggests it isn't really a lot of sodium. $\endgroup$ – matt_black Feb 5 at 13:52
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Note that this doesn't mean Coca-Cola typically contains 40 mg sodium per serving. Instead, that's likely an upper limit designed so that, with normal variation, the product will still be in compliance.

FDA regulations specify that that, for "Third Group" nutrients like sodium, the actual amount must not exceed the label amount by more than 20%. Thus companies are required to take enough samples of their product to determine the variation, and use a label amount high enough to ensure that, even with the variation, the actual amount doesn't exceed the label amount by 20%.

Here's a screenshot from FDA's website (https://www.fda.gov/food/guidanceregulation/guidancedocumentsregulatoryinformation/labelingnutrition/ucm063113.htm) showing an example of how this might be done for sodium. Note that the mean, found from an analysis of 96 samples, is 95.81 mg per serving. However, based on the stdev, a one-sided 95% prediction interval estimates that (within this interval) the maximum amount of sodium would be 120 mg/serving, so that's what is listed on the label. Given this, the product would be considered in compliance if the actual amount of sodium is <= 144 mg/serving.

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