Saturday, Oct 17, 2009
Hard-boiled eggs are harder to peel the fresher they are.
Ironically, the hard-cooked eggs that are most difficult to peel are usually "fresh" eggs. As mentioned above, properly handled eggs that are a few days old contain more CO2 than old eggs, so their albumen has a lower (less basic) pH value. The difficulty you may encounter in removing the shell of a fresh hard-cooked egg has been associated with the low pH of the albumen. As stored eggs lose CO2, the albumen pH rises; when these eggs are hard-cooked, they are easier to peel. Thus, eggs that have been stored in the refrigerator for about a week are usually easier to peel when hard-cooked... Regulations require that the sell-by date be no more than 30 days from the packing date. If more than 23 days remain before the sell-by date, the eggs may not peel well.
Egg Basics for the Consumer: Packaging, Storage, and Nutritional Information, Bradley and King, University of California, Davis, Division of Agriculture and Natural Resources, 2004, http://anrcatalog.ucdavis.edu/pdf/8154.pdf.