It seems contrary to most cooking advice, which typically urges freshness, freshness at any expense. But there are times when you actually want something that’s been sitting around for a spell. Cheeses and wines get better with age, of course, and eggs become more versatile. That’s because older eggs—eggs you’ve had for at least three or four days—are better for boiling than fresh eggs. Why’s that? It doesn’t have anything to do with flavor, but with form. As an egg ages, it begins to change chemically in ways that will make the eggs much, much easier to peel. It will be less likely for shells to cling stubbornly to the cooked whites, and thus less likely to finish the job with a lumpy egg missing chunks of white where you desperately tried to rid the thing of its shell.
This all has to do with pH: As soon as an egg is laid, its pH of about 8.0 begins to change, slowly increasing, making it more alkaline. To hear the ever-brilliant author Harold McGee tell it in his classic On Food and Cooking, the fresher an egg is, “the inner membrane tends to adhere to the albumen”—that’s the egg white—”whereas… after three days of refrigeration, around 9.2, the problem no longer exists.” That is, an older egg has a less sticky, less clingy membrane between the shell and the egg white, and the shell will release its contents much more happily.
What’s more, as the egg ages, it actually loses moisture, meaning that there’s more space between the white the shell. This, of course, makes for even easier peeling.
A final bit of insurance: Give just-boiled eggs an ice water bath as soon as they emerge from the pot, cracking them slightly before putting them in the bowl. The cold water will make the hot egg pull away from its shell, and the water will seep through the crack in the shell and wiggle its way between the shell and the white. Ta-da! Perfect boiled eggs—hard- or soft-cooked.
So, save your freshest eggs for frying (one more reason: the yolks of more alkaline eggs are more prone to breaking as soon as they hit the pan) and put your older eggs towards egg salad, deviled eggs, and the like.
My technique for perfect boiled eggs:
Fill a pot with enough water to cover an (old) egg by an inch, and bring to a boil. When the surface is rolling, use a spoon to gently lower an egg (cold and straight from the refrigerator) into the water. Cook exactly 5 minutes for a set white and runny yolk, 7 minutes for a firmer white and a creamy, jammy yolk, and 9 minutes for a fully set yolk. Prepare an ice bath while the eggs boil. Drain the eggs from the pot and crack them lightly against the countertop before slipping them into the ice water. Let sit in the water at least a minute, then peel.