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?
鈥� The reason some eggs are difficult to peel is because they are too fresh. The shells of such eggs are always difficult to remove cleanly. Those a few days older are much easier. This is all down to how the chemistry of the albumen, or egg white, changes over time. This is also why, if you ever try to make meringue with fresh egg whites, they won鈥檛 easily whisk up and become thick. Use older egg whites for them.
Jackie Jones, Brighton, East Sussex, UK
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鈥� This only happens with very fresh eggs. We have chickens and are familiar with this problem. It is the same whether the egg is hard or soft-boiled.
The albumen of fresh eggs is more acidic, and this makes it stick to the inner shell membrane more strongly. Fresh egg white has a pH between 7.6 and 7.9 and a cloudy appearance due to the presence of dissolved carbon dioxide, which is a weak acid. As the egg ages, the shell鈥檚 outer coating slowly wears off and the egg becomes more porous. The carbon dioxide dissipates and the pH increases to around 9.2. At this pH, the inner membrane doesn鈥檛 stick as much to the albumen so the shell peels off more easily.
Jo Watson, Tadley, Hampshire, UK
鈥� If you want to find out how old your eggs are, put them in a bowl of water. Fresh eggs will sink on their sides (too fresh for hard-boiling), older eggs will sink at a tilted or in an upright position (perfect for hard-boiling). Eggs that are too stale to use will float.
Katherine Miller, Toronto, Canada
鈥� I have a method for peeling eggs that works well even if they are very fresh. Run cold water into the pan to cool the egg, then crack it round its middle. With spoon and egg in the water, lever up a section of shell using the tip of the spoon. Slide the spoon into the crack between the white and the membrane, and rotate it around the egg making sure both egg and spoon stay wet.
鈥淪hips don鈥檛 just mark their paths on the water. Their routes can be traced by contrails in the clouds too鈥�
You should then be able to remove the half shell intact. Do the same with the other half. This works even for soft-boiled eggs.
David Newton, Ipswich, Suffolk, UK
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