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I recently ordered some dish from a local food delivery company. The dish, among other ingredients, contained hard-boiled eggs. The ingredient list read the following:

[...] Hard-boiled eggs (egg, citric acid), [...]

Due to that formatting, the citric acid was definitely used for the eggs, not for the dish as a whole. I am wondering what the purpose of using citric acid for cooking hard boiled eggs could be. I am not sure how/in what quantity/when it is added to the eggs. I could think of a few possible reasons to using it, however, I am not sure if any of these is real. My ideas are:

  • Perhaps, given that it is acid, it helps removing the bacteria and/or feces remnants from the shell, or
  • Given the lime content of egg shells and the fact that lime is pretty reactive to some acids, it might help with peeling. It sounds reasonable as we are talking about a food delivery company, probably cooking eggs up in the quantities of the hundreds to thousands.

These are just my two cents, does anyone know the (possibly) real reason behind it?

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    Often the peeled eggs are stored in water and they can turn slightly brown. A touch of lemon keeps them more white. – paparazzo Oct 25 '17 at 15:55
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US patent EP0020011 A2 describes a process of packaging shelled hard boiled eggs where the egg is dipped in a citric acid solution to prevent discoloration of the yolk at the white-yolk interface. I would guess that’s what is going on in this case.

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    Thanks for your remark, I was wrong about the translation, fixed it. In my country, we call it "lemon acid" for some unknown reason. – Balázs Oct 25 '17 at 11:39
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    Reason not all that mysterious: Citric, citrus, lemons - and the taste is basically lemon with a lack of the complexity of actual lemon, but easily 90% of the way there ( I made some "citric acid lemon ice" as an experiment so that's a first-hand assessment. Citric acid, sugar and water.) – Ecnerwal Oct 25 '17 at 17:47
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Citric acid is used after eggs are cooked and peeled to prevent grow of pathogenic bacteria especially Listeria monocytogenes. This bacteria should be readily destroyed during the boiling of eggs due to its low thermal resistance (D) value, however hard-boiled eggs may be subjected to post-processing contamination by food handlers or work surfaces during preparation and packaging. Post processing storage in citric acid is used as one of the solutions to make sure hardboiled eggs are safe to eat.

Citric acid also helps to get rid of 'grey ring' which might form around the yolk if eggs are overcooked but primary purpose of citric is food safety

Citric acid will not increase eggs peelability. It is age of egg which defines it. Fresher egg is more acidic and peels bad. While egg ages its pH increases and peelability improves.

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