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I like hard-boiled eggs. When I peel one, the shell and underlying membrane sometimes separate cleanly from the albumen, leaving a perfectly smooth white egg. At other times the shell, membrane and first layer of the albumen all stick together and are impossible to separate, so I end up with a pitted mess. Why the difference? Is it something to do with the egg itself, the way I cook it, or the way I leave it to cool afterwards?

Alistair Scott, Gland, Switzerland

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