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Teacher/Leader Guide REVISED 2007 PUBLICATION 408-031 THEEgg-citing Egg Teacher/Leader Guide 707 U.S.C. 18 THEEgg-citing Egg Teacher/Leader Guide Curtis Novak, Extension Specialist, Poultry Science, Virginia Tech Catalina Roche, Graduate Student, Poultry Science, Virginia Tech Kathleen Jamison, 4-H Curriculum and Learning Specialist, Virginia Tech www.ext.vt.edu Produced by Communications and Marketing, College of Agriculture and Life Sciences, Virginia Polytechnic Institute and State University Virginia Cooperative Extension programs and employment are open to all, regardless of race, color, national origin, sex, religion, age, dis- ability, political beliefs, sexual orientation, or marital or family status. An equal opportunity/affirmative action employer. Issued in furtherance of Cooperative Extension work, Virginia Polytechnic Institute and State University, Virginia State University, and the U.S. Department of Agriculture cooperating. Mark A. McCann, Director, Virginia Cooperative Extension, Virginia Tech, Blacksburg; Alma C. Hobbs, Administrator, 1890 Extension Program, Virginia State, Petersburg. VT/0307/W/408031 707 U.S.C. 18 707 U.S.C. 18 THE Egg-citing Egg 1 Cracking the Common Egg reach retail stores within 24 to 48 hours after they are laid and are therefore fresher than the so-called “The Egg-citing Egg” 4-H project is designed to “farm fresh” eggs of yesteryear. acquaint youth with the avian egg, its parts, and how they relate to human nutrition. Commercial Egg Structure and Composition egg production and marketing are also discussed. The major parts of the egg are shown in Figure Not only are eggs one of nature’s most nutritious 1. The yolk is the living center of the egg, and in foods, they can become a classroom teaching the fertilized egg it is the nutritive material that resource. This publication is designed to be used in supports the growth of the embryo. The yolk is conjunction with “The Egg-citing Egg” record book located near the center of the egg, and in the for 4-H’ers. freshest eggs tends to rise to the top of the albumen that surrounds it. The yolk is primarily composed Egg Lore of fat but also includes proteins, vitamin, minerals, and water. The albumen (white) is a clear, viscous Eggs have been important to man for many material that sometimes has a greenish-yellow cast centuries. Since before Biblical times, they have caused by the pigment ovoflavin. The albumen is been considered a delicacy. They have been made up of protein and water. In very fresh eggs, associated with science, sports, and superstition, you will notice thick albumen surrounding the and were important in pagan and Christian custom. yolk, and a thinner albumen on the outside. The To many primitive cultures, eggs signified the return albumen is surrounded by two shell membranes Egg-citing Egg of life following the winter season, and have been that are cemented to each other, except at the blunt offered to idols at spring festivals by some tribes in end where an air cell is formed between the two Africa and South America. To the Egyptians, eggs membranes after the egg is laid. At each end of the signify the restoration of mankind following the yolk is a twisted, rope-like structure of concentrated deluge. The Jews use eggs in the Passover Feast to albumen called the “chalazae” (kuh-lay-zee), which signify deliverance from bondage and to celebrate anchor the yolk to the membranes surrounding their departure from Egypt. Our modern custom the albumen and serve to keep the yolk centered of decorating eggs at Easter is a symbol of the in the eggshell. Chalazae vary in size and do Resurrection, but history reveals that the custom not negatively affect cooking performance or originated in pre-Christian times. nutritional value. In fact, they are most noticeable in fresh eggs. Modern Egg Production Although proportions vary, albumen makes up As recently as 40 years ago, practically every farm about 58 percent of the weight of the whole egg had a small flock of chickens. Hens were allowed with the yolk and shell representing 31 percent and the “run of the farm” and were fed table scraps and 11 percent, respectively. Water makes up about 74 a little grain. The farmer used the eggs he needed percent of the edible portion of the egg and is the for home consumption and offered the remainder medium in which chemical and physical changes for sale to local retail merchants, neighbors, and occur. Protein makes up about 13 percent, fat 12 friends. The “egg money” generated was in direct percent, and ash 1 percent of the edible portion of relation to the time spent in this small enterprise the whole egg. and the market demands of the community. The egg yolk contains orange, red, and yellow This type of egg producer would be awestruck by pigments which belong to the carotenoid groups. a modern egg production-processing operation. Carotenoids are long-chained hydrocarbon Today’s mass production is highly scientific and compounds of plant origin. Animals cannot almost totally automated. Hens are housed in synthesize lutein, though they have the ability to environmentally controlled houses under controlled absorb carotenoids from their diet and deposit them lighting and are fed computer-formulated diets. into tissue. Metabolically, plants use carotenoids to Eggs are collected on conveyor belts, washed, protect against light damage to chlorophyll. Animals graded, sized, and automatically packaged for use the absorptive and antioxidant properties of direct shipment to retail stores. In many cases, eggs carotenoids in a similar fashion (Novak and Troche, 707 U.S.C. 18 707 U.S.C. 18 THE 2 Egg-citing Egg Shell • Outer covering of egg, composed of calcium carbonate. Air cell • May be white or brown, • Pocket of air formed at depending on breed of the large end of the egg. chicken. • Color does not affect • Caused by contraction of quality, cooking contents during cooling characteristics, or after laying. nutritional value. • Increases in size with age. Yolk • Yellow portion of egg. Shell Membranes • Color varies with feed • Two membranes of the hen, but doesn’t – inner and outer shell indicate nutritional membranes – surround content. the albumen. • Major source of • Provide protective vitamins, minerals and barrier against bacterial fat (The yolk contains penetration. more than 90 percent of the calcium, iron, • Air cell forms between phosphorus, zinc, these two membranes. thiamin, B6, folate, and B12, and 89 percent of Thin Albumen the panthothenic acid • Nearest to the shell. [9 items]). The white does not contain more • Spreads around thick than 90 percent of any white of high quality nutrient, but contains egg. over 80 percent of the magnesium, sodium, and Thick albumen (White) niacin). • Excellent source of • Germinal disc. riboflavin and protein. Vitelline (Yolk) membrane • Stands higher and spreads less than thin • Clean seal that holds egg yolk. white in high quality eggs. Chalazae • Thins and becomes • Twisted, cordlike strands indistinguishable from of egg white. thin white in low quality eggs. • Anchor yolk in center of egg. • Prominent chalazae indicate high quality. 707 U.S.C. 18 707 U.S.C. 18 THE Egg-citing Egg 3 2006). Yolk color can vary from dark orange-red to light yellow, depending on the hen’s food. Most eggs on the market today have a uniformly colored yolk because the hens are caged and fed a standard corn/soybean-meal diet. Egg Size and Egg Quality There is no relationship between size and grade of eggs. Sizes of eggs range from Jumbo to Peewee. While one or two eggs in a dozen may be smaller by one size or larger than others, the weight of the whole carton of eggs is what counts. Size is expressed in ounces per dozen. Eggs offered for sale in retail stores are typically graded. They are also grouped into size or weight Egg Candler categories. Grade A eggs have the same qualities whether they are small or large. Both grade and size affect price. Some eggs are sold as ungraded. table below). They are graded differently from USDA eggs are candled and graded according interiors in that each grade (AA, A, and B) is further to U.S. Department of Agriculture grading broken into three grades; i.e., AA’s are classified as specifications. Candling is a method for examining either a 1, 2, or 3, 1 being the best example of a AA the interior of the egg without breaking the shell. egg and 3 being the worst example of a AA egg. Eggs are passed before a bright light which makes Small blood or meat spots are sometimes found in it possible to judge albumen quality and location the albumen or on the surface of the yolk. This is of the egg yolk. The light also reveals the size of caused by the rupture of a small blood vessel while the air cell or any interior defects and makes any the egg is being formed. These eggs are referred to abnormalities in the shell visible. The air cell is as “loss eggs”. On occasion, a carton egg will have also a factor in candling. As an egg ages, moisture a blood or meat spot. These imperfections can be escapes via pores in the cell. The longer an egg sits, easily removed and the egg can be used for general the larger the air cell becomes. Grade AA eggs have cooking. air cells less than one-eighth of an inch in depth. Grade A eggs have air cells between one-eighth Dirty, cracked, or defective eggs are removed and three-sixteenths of an inch in depth and Grade during the grading process and are not offered B air cells are larger than three-sixteenths of an for sale in retail stores.
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