Additional Math Pages & Resources

Thursday, February 18, 2010

Eggzactly, Part 2

Yesterday I talked about units of measure for eggs. Specifically, sizing which is based on the weight of 12 eggs. An individual egg can be larger or smaller as long as the average in the carton is equal to USDA standards.

What I haven't covered yet are quality ratings. They are:
  • Dirty
  • Cracked
  • B
  • A
  • AA 
How do eggs get dirty or cracked? Well, chickens walk around, get dirt or poop on their feet, and that gets on the eggs. Hens may lay them while standing up so the eggs drop. If it's a hard surface, the eggs can crack. Washing doesn't necessarily remove all the flaws.

Dirty and Cracked mean what they say, and eggs graded this way (after being washed!) are only for sale to factories or commercial egg processors. The assumption is these commercial egg users will process them quickly and in a controlled and sanitary manner. Besides that, the eggs are most likely to be used without anyone seeing the shell anyway (liquid, powdered, separated, etc.).

I suspect most of us wouldn't want to buy anything less than A or AA anyway. When did you last see a B egg?

But how are those ratings determined? It is based on the albumen (white) being measured using the Haugh Scale. That's our indication of freshness. The process was developed by Raymond Haugh, in 1937.

An egg is stored overnight at a specific temperature (40° F or 4° C), weighed in a room between 45-65° F, then broken out onto a clean flat surface. The depth of the white is measured with a precision micrometer, halfway between the yolk and the outer edge of the white. If you want to do the calculations, here's the formula, though I have to warn you it is beyond elementary school mathematics.

HU = 100 log(h-.01 x 5.6745 (30w.37 - 100) + 1.9)

or the simplified version 

HU = 100 log(h - 1.7w.37 +7.57)

The variables in the formula are h = height of white in mm, and w = weight of the egg in grams.

I read a fascinating (yawn) paper that recommended further simplification - just measure the height of the albumen and leave it at that. That approach had an almost perfect correlation to Haugh scores, and takes a fraction of the time to achieve. Sounds good to me. Sometimes less math is better.

Here is the criteria for grading:
  • B eggs have an HU ≤ 60
  • A eggs have an HU = 60-72
  • AA eggs have an HU ≥ 72
This simply means the freshest eggs have the tallest albumens. Over time, the whites collapse and are lower (closer to the table top).

We had to have an omelette for dinner last night because of all the eggs I broke onto plates, taking photos and comparing...

PS - I also found a new site today - It discussed units for measuring almost anything!


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