QUESTION:I note that you can buy grades “AA” and “A” eggs. What’s the difference? (Asked by a curious column-reader near the dairy section.)

REPLY: The U.S. Department of Agriculture has developed quality grade standards for shell eggs. There are now three grades: AA, A and B. There was a grade C, but this was dropped. (Not sure why -- maybe grade inflation?)

The grade standards define and measure the quality of the egg in terms of appearance and condition of the shell, as well as the interior quality of the albumen (white) and yolk. Here are some general criteria:

-- Shell: AA and A grades must have a clean, unbroken shell with normal appearance. Grade B egg shells may be slightly stained, have abnormal shapes, and have thin or ridge spots.

-- Air cell (the space between the shell membranes usually found in the large end of the egg): When held upright, the large end of the egg has a smaller air cell in the AA grade.

-- Whites: AA eggs must have clear and firm whites. Grade A whites must be clear and reasonably firm when twirled. Grade B whites appear weak and watery.

-- Yolks: AA yolks stand tall. Grade A yolks are upstanding but round, and B yolks are enlarged and flattened.

You may wonder how all this grading is done. It used to be done by hand using candling (looking through the egg with a light behind it). However, most inspections today are done by machine.

Oh yes, size. I almost forgot. The USDA has also developed official weight (size) classes for shell eggs. There are six weight classes for consumer eggs: (1) Jumbo, (2) Extra Large, (3) Large, (4) Medium, (5) Small, and (6) Peewee. Basically, the classes define a minimum net weight per dozen eggs. The weight or size sorting is done during the grading process.

So, you can have Grade AA peewee eggs. I’ve been looking for a dozen of them. I could have three or four eggs for breakfast without having to worry about cholesterol.

C.P.S. (Curious Postscript): “If you try to fail, and succeed, which have you done?” —George Carlin

Curious about something? Send your questions to Dr. Jerry D. Wilson, College of Science and Mathematics, Lander University, Greenwood, SC 29649, or e-mail jerry@curiosity-corner.net. Selected questions will appear in the Curiosity Corner. For Curiosity Corner background, go to www.curiosity-corner.net.