On food and cooking the science and lore of the kitchen ( PDFDrive ) 164

cluster, so the white of an older egg tends to be clear, not cloudy And the white gets progressively more runny with time: the proportion of thick albumen to thin, initially about 60% to 40%, falls below 50–50 The relatively minor change in yolk acidity is less important than a simple physical change The yolk starts out with more dissolved molecules than the white, and this osmotic imbalance creates a natural pressure for water in the white to migrate across the yolk membrane At refrigerator temperatures, about 5 milligrams of water cross into the yolk each day This influx causes the yolk to swell, which stretches and weakens the yolk membrane And the added water thins the yolk dramatically A Home Test Finally, the egg as a whole also loses moisture through its porous shell, so the contents of the egg shrink, and the air cell at the wide end expands Even an oil-coated egg in a humid refrigerator loses milligrams of water to evaporation each day The cook can use this moisture loss to estimate the freshness of an egg A new egg with an air space less than 1/8 inch/3 mm deep is denser than water and will sink to the bottom of a bowl of water As an egg ages and its air cell expands, it gets progressively less dense, and the wide end of the egg rises higher and higher in the water An egg that actually floats is very old and should be discarded Around 1750, the English cookbook author Hannah Glasse gave two ways of determining the freshness of an egg, an important talent at a time when it might have been sitting for some time in an odd corner of the yard One is to feel how warm it is — probably less than reliable — but the second indirectly assays the air cell: “[Another way] to know a good egg, is to put the egg into a pan of cold water; the fresher the egg the sooner it will fall to the bottom; if rotten, it will swim at the top.” ... and will sink to the bottom of a bowl of water As an egg ages and its air cell expands, it gets progressively less dense, and the wide end of the egg rises higher and higher in the water An egg that actually floats... corner of the yard One is to feel how warm it is — probably less than reliable — but the second indirectly assays the air cell: “[Another way] to know a good egg, is to put the egg into a pan of cold water;... milligrams of water to evaporation each day The cook can use this moisture loss to estimate the freshness of an egg A new egg with an air space less than 1/8 inch/3 mm deep is denser than water and