|
|||
|
|
||
|
|
|
|
|
|||
|
|
||
Food Science Sample LessonFS117 Egg Production
Maximum production of top-quality eggs starts with a closely controlled breeding program emphasizing favorable genetic factors. The White Leghorn type hen dominates today's egg industry. This breed reaches maturity early, uses its feed efficiently, has a relatively small body size, adapts well to different climates and produces a relatively large number of white-shelled eggs, the color preferred by most consumers. In the major egg producing states, flocks of 100,000 laying hens are not unusual, and some flocks number more than 1 million. Each of the 235 million laying birds in the United States produces from 250 to 300 eggs a year. In today's egglaying facilities, temperature, humidity and light are all controlled and the air is kept circulated. The building is well-insulated, windowless (to aid light control) and is force-ventilated. Most new construction favors the cage system for sanitation and efficiency. Because care and feeding of hens, maintenance, sanitation and egg gathering all take time and money, there is a strong trend toward automation whenever possible. PROCESSING The moment an egg is laid, physical and chemical changes begin to reduce freshness. In most production facilities, automated gathering belts gather and refrigerate eggs frequently. Gathered eggs are moved into refrigerated holding rooms where temperatures are maintained between 40 and 45 F (5 and 7 C). Humidity is relatively high to minimize moisture loss. Carton Dates: Egg cartons from USDA-inspected plants must display a Julian date (a number 1 through 365) indicating the date the eggs were packed. Although not required, they may also carry an expiration date beyond which the eggs should not be sold. In USDA-inspected plants, this date cannot exceed 30 days after the pack date. Plants not under USDA inspection are governed by state laws. Fresh shell eggs can be stored in their cartons in the refrigerator for 4 to 5 weeks beyond the Julian date with only insignificant loss of quality. STRUCTURE AND CHARACTERISTICS The structure and characteristics of an egg include its color, shell, white, yolk, air cell, chalaza, germinal disc and membranes. Color: Egg shell and yolk color may vary, but color has nothing to do with egg quality, flavor, nutritive value, cooking characteristics or shell thickness. Shell: The color comes from pigments in the outer layer of the shell and may range in various breeds from white to deep brown. The breed of hen determines the color of the shell. The egg's outer covering accounts for about 9 to l2 percent of its total weight, depending on egg size. The shell is the egg's first line of defense against bacterial contamination. The shell is largely composed of calcium carbonate (about 94 percent) with small amounts of magnesium carbonate, calcium phosphate and other organic matter including protein. White: Egg albumen in raw eggs is opalescent and does not appear white until it is beaten or cooked. A yellow or greenish cast in raw white may indicate the presence of riboflavin. Cloudiness of the raw white is due to the presence of carbon dioxide which has not had time to escape through the shell -- and thus indicates a very fresh egg. Yolk: Yolk color depends on the diet of the hen. Artificial color additives are not permitted. Gold or lemon-colored yolks are preferred by most buyers in the United States. Yolk pigments are relatively stable and are not lost or changed in cooking. Air Cell: The air cell is the empty space between the white and shell at the large end of the egg. When an egg is first laid, it is warm. As it cools, the contents contract and the inner shell membrane separates from the outer shell membrane to form the air cell. Chalaza: These are ropey strands of egg white which anchor the yolk in place in the center of the thick white. They are neither imperfections nor beginning embryos. The more prominent the chalazae, the fresher the egg. Germinal Disc: The germinal disc is the channel leading to the center of the yolk. When the egg is fertilized, sperm enter by way of the germinal disc, travel to the center and a chick embryo starts to form. Membranes: Just inside the shell are two shell membranes, the inner and outer. After the egg is laid and begins to cool, an air cell forms between these two layers at the large end of the egg. The vitelline membrane, a third membrane, covers the yolk. Its strength protects the yolk from breaking. The vitelline membrane is weakest at the germinal disc and tends to become more fragile as the egg ages. NUTRITIONAL VALUE The yolk or yellow portion makes up about 33 percent of the liquid weight of the egg. It contains all of the fat in the egg and a little less than half of the protein. With the exception of riboflavin and niacin, the yolk contains a higher proportion of the egg's vitamins than the white. The yolk also contains more phosphorus, manganese, iron, iodine, copper and calcium than the white, and it contains all of the zinc. The yolk of a large egg contains about 59 calories, while the whole egg including the albumen contains about 75 calories (kcal) of energy. Also known as egg white, albumen contains more than half the egg's total protein, niacin, riboflavin, chlorine, magnesium, potassium, sodium and sulfur. Protein from the yolk and the albumen provides humans with a high quality protein containing all of the essential amino acids. GRADING Classification is determined by interior and exterior quality and designated by the letters AA, A or B. In many egg packing plants, the USDA provides a grading service for shell eggs. Its official grade shield certifies that the eggs have been graded under federal supervision according to USDA standards and regulations. The grading service is not mandatory. Other eggs are packed under state regulations which must meet or exceed federal standards. In the grading process, eggs are examined for both interior and exterior quality and are sorted according to weight (size). Grade quality and size are not related to one another. In descending order of quality, grades are AA, A and B. No difference in nutritive value exists between the different grades. Because production and marketing methods have become very efficient, eggs move so rapidly from laying house to market that consumers find very little difference in quality between Grades AA and A. Although Grade B eggs are just as wholesome to eat, they rate lower in appearance when broken out. Almost no Grade B eggs find their way to the retail supermarket. Some go to institutional egg users such as bakeries or foodservice operations, but most go to egg breakers for use in egg products.
SIZE Several factors influence the size of an egg. The major factor is the age of the hen. As the hen ages, her eggs increase in size. The breed of hen producing the egg is a second factor. Weight of the bird is another. Environmental factors that lower egg weights are heat, stress, overcrowding and poor nutrition. All of these variables are of great importance to the egg producer. Even a slight shift in egg weight influences size classification -- and size is one of the factors considered when eggs are priced. Egg sizes are Jumbo, Extra Large, Large, Medium, Small and Peewee. Medium, Large and Extra Large are the sizes most commonly available. Sizes are classified according to minimum net weight expressed in ounces per dozen as shown in Table 1.
Table 1. Weight Classes for Shell Eggs Size Weight (oz) per dozen ----- --------------------- Jumbo 30 Extra large 27 Large 24 Medium 21 Small 18 Peewee 15 Blood Spots: Blood spots are also called meat spots. These are occasionally found on an egg yolk. These tiny spots do not indicate a fertilized egg. Rather, they are caused by the rupture of a blood vessel on the yolk surface during formation of the egg or by a similar accident in the wall of the oviduct. Less than 1 percent of all eggs produced have blood spots. COOKING FUNCTIONS While eggs are widely known as breakfast entrees, they also perform in many other ways for the knowledgeable cook. Their cooking properties are so varied, in fact, that they have been called "the cement that holds the castle of cuisine together." Eggs can bind ingredients as in meat loaves or croquettes. They can also leaven such baked high rises as souffles and sponge cakes. Their thickening talent is seen in custards and sauces. They emulsify mayonnaise, salad dressings and Hollandaise sauce and are frequently used to coat or glaze breads and cookies. They clarify soups and coffee. In boiled candies and frostings, they retard crystallization. As a finishing touch, they can be hard cooked and used as a garnish. FERTILE EGGS Eggs which can be incubated develop into chicks. Fertile eggs are not more nutritious than nonfertile eggs, do not keep as well as nonfertile eggs, and are more expensive to produce. ORGANIC EGGS Organic eggs are from hens fed rations having ingredients that were grown without pesticides, fungicides, herbicides or commercial fertilizers. No commercial laying hen rations ever contain hormones. Due to higher production costs and lower volume per farm, organic eggs are more expensive than eggs from hens fed conventional feed. The nutrient content of eggs is not affected by whether or not the ration is organic. STORAGE Eggs can be stored at 30 F (-1 C) for up to six months in the shell. They can be frozen out of the shell for extended storage. The large quantities of eggs required by the food manufacturing industry are preserved by freezing. Eggs may be frozen as the whole egg (minus shell), separately as the white and yolk, or in varying combinations. Also, after removal from the shell, eggs can be dried (dehydrated) as whole eggs, whites or yolks. The methods of dehydrating eggs include spray drying, tray drying, foam drying and freeze-drying. SALMONELLA The inside of the egg had once been considered almost sterile, but recently a bacterial organism, Salmonella enteritidis, has been found inside some eggs. Only a very small number of eggs might contain Salmonella enteritidis. Even in areas where outbreaks of salmonellosis have occurred, tested flocks show an average of only about 2 to 3 infected eggs out of each 10,000 produced. The FDA considers these foods "potentially hazardous." The designation is not cause for alarm. It simply means that these foods are perishable and should receive refrigeration, sanitary handling and adequate cooking. Lack of attention to these details can make any food a "hazardous" food. EGG SUBSTITUTES With all of the attention paid to cholesterol, the high level of cholesterol (about 240 mg) in eggs has caused consumers to reduce their consumption of eggs. Food manufactures have taken different approaches to reducing the cholesterol in egg, from physically separating the cholesterol from the yolk to formulating yolks from other products and combining these with the albumen. These products are sold as egg substitutes. A different approach to reducing the cholesterol and changing the fat content of eggs is to change the genetics of the chicken so they produce the type of egg desired. EXERCISES: 1. Allow some eggs to set at room temperature for a couple of days to age them. Crack them on a flat surface and compare them to cracked eggs that have been kept refrigerated. What changes do you notice? 2. Four egg cartons display the following Julian dates: 68, 120, 260 and 300. What calendar dates do these represent, assuming it is not a leap year? 3. Compare an egg substitute with real eggs. Report on your findings. 4. Compare the calories in one egg to that in a fast food hamburger, candy bar or other food you eat often and report your findings. TEST:
1. Laying hens produce approximately how many eggs per year? 2. Eggs are usually gathered only once a day in large facilities. TRUE or FALSE? 3. What characteristic of the hen determines the color of the shell? 4. __________ color depends on the diet of the hen. 5. The __________ of the hen is the major factor in the size of the egg. 6. A grading service is mandatory for eggs. TRUE or FALSE? 7. Of the three grades, AA, A and B, which grade spreads out more when cracked?
8. About how many calories does a whole egg contain? 9. What membrane protects the yolk from breaking? 10. Which part of the egg -- the yolk or white -- contains most of the protein?
11. Eggs can be dehydrated. TRUE or FALSE? END STUDENT SECTION
TEACHER'S GUIDE
FS117 Egg ProductionOBJECTIVE: Students will realize what is involved in the production and identification of quality eggs and how quality is maintained. PREPARATION: Take the following steps to prepare for this lesson: 1. Read and review this lesson material. 2. Study the production and grading of eggs as detailed in a poultry textbook or at the Agricultural Marketing Service of the USDA (Internet site listed below). 3. Review recipes and determine how eggs are used in cooking. 4. Find promotional materials on the healthy aspects of eggs and review the role of cholesterol in heart disease. For example, you could visit the American Egg Board Internet site listed below. INTERNET SITES:
** American Egg Board
** American Egg Board - Learn More about Eggs
** American Egg Board - Egg Safety
** USDA Agricultural Marketing Service - U.S. Standards, Grades, and Weight Classes for Shell Eggs IMPORTANT TERMS: automated, organic, Julian date, albumen, air cell, chalaza, germinal disc, vitelline membrane, blood spot. EXTENSION: Allow students to candle eggs and look for cracks and the air cell. Also some fertile eggs can be incubated in a simple incubator and students can candle these as they develop. Eggs can be candled with a strong flashlight or a simple candling box can be constructed. EXERCISE ANSWERS: 1. Eggs left at room temperature should appear flatter and watery. 2. March 9, April 30, September 17, October 27 3. Often egg substitutes have some egg components such as the albumen along with some oil and food coloring. 4. One egg contains 75 calories; a regular candy bar contains about 280 calories, and a fast food hamburger with cheese contains about 730 calories. TEST KEY:
1. Laying hens produce approximately how many eggs per year? Correct answer: C. 250 to 300 2. Eggs are usually gathered only once a day in large facilities. TRUE or FALSE? FALSE. In most production facilities, automated gathering belts gather and refrigerate eggs frequently. 3. What characteristic of the hen determines the color of the shell? The breed 4. Yolk color depends on the diet of the hen. 5. The age of the hen is the major factor in the size of the egg. 6. A grading service is mandatory for eggs. TRUE or FALSE? FALSE. 7. Of the three grades, AA, A and B, which grade spreads out more when cracked? Grade B
8. About how many calories does a whole egg contain? Correct answer: B. 75 calories 9. What membrane protects the yolk from breaking? Vitelline 10. Which part of the egg -- the yolk or white -- contains most of the protein? The white 11. Eggs can be dehydrated. TRUE or FALSE? TRUE. CROSSWORD PUZZLE ANSWERS:
Across: 2. Size, 3. White, 5. Calcium, 8. Shell, 9. Yolk, 10. USDA, 11. Jumbo, 12. Vitelline, 13. Air. END
To subscribe to AgEdNet.com or
for a "free trial", |
||||||||
|
HOME | SUBSCRIBERS | VISITORS | ORDER | CONTACT US | TERMS & USAGE Copyright © 1995-2008 Stewart-Peterson. All Rights Reserved. STEWART-PETERSON and AGEDNET.COM are Registered Trademarks of Stewart-Peterson, Inc. AgEdNet.com®, a service of Stewart-Peterson, Inc. 137 South Main Street, West Bend, WI 53095 |
