Food Processing

FACTORS IN PRODUCTION AND QUALITY OF EGGS

Chicken eggs represent the bulk of egg production in the United States and Europe. Though some laying hens are known to produce an egg every day, in commercial installations the average for layers is about 220 eggs per year. In several parts of the world, the duck is important as an egg producer and the egg-laying ability of certain types excels that of chickens. Some ducks produce from 300 to 360 eggs a year, but the average is much less. Duck eggs are larger and heavier than chicken eggs, and are used as food in western Europe and the Orient. Geese are raised extensively in Poland and some of the western European countries, and their eggs are often used for foods. Commercial production of turkey and pigeon eggs is almost entirely confined to those used for producing turkey poults and young pigeons (squabs). Pheasant and quail eggs provide birds for hobby or sport use.

Selection of laying hens.

Chickens are the world's most widely distributed domestic fowl. Commercially, the major chicken breeds for egg production include several of the varieties of the Leghorn in the Mediterranean class and such varieties as white Plymouth Rock and New Hampshire breeds in the dual-purpose, or American class. Breeders have selected birds with high rates of egg production and by inbreeding, single crossing of inbred lines, or multiple crossing of lines, have evolved pullets (immature hens) that can maintain good performance for a year or more. Ordinarily, pullets are placed in production at 5 to 6 months of age and are kept as layers until they are about 18 months old. While older layers produce large eggs, the shell usually does not have good quality and production is reduced after one year of laying.

Cleaning and oiling.

In the United States shell eggs are shipped from the producer to the packing station in cardboard containers holding either 15 dozen or 30 dozen eggs separated by fillers and flats. Such eggs are unsorted as to size and grade. When received at the plant, eggs are placed into a cool 50 {degree}

-60

F (10

-16

C) humidified room.

Soiled eggs cause heavy financial losses. Dirty eggs bring less per dozen because the cost of cleaning them is high and their keeping quality is poor. Such eggs are cleaned by washing or by dry cleaning the dirty or stained area with an abrasive emery cloth or fine sandpaper.

When eggs are washed, a solution at least 20 {degree} F warmer than the egg and having a temperature of 90 F (32 C) or more is used so that the egg's interior will not contract and allow polluted water to be drawn into the shell. The washed egg is rinsed immediately with warm water containing a sanitizer and dried before packing. Dry cleaning is little used because it is slow, does not do a thorough job, and often results in excessive breakage.

Oiling eggs reduces evaporation of moisture and replaces the cuticle lost during washing. As soon as possible after the eggs are laid or washed, a fine film of light-weight mineral oil, which is colourless, odourless, and tasteless, is sprayed over the egg shell to seal the pores. Oiling also cuts weight loss and halts air cell expansion.

The keeping quality of cleaned eggs also can be improved by holding them in water at 130 {degree} F (55 C) for 15 minutes or at slightly higher temperatures for shorter periods of time. This form of thermostabilization causes a slight thickening of the albumen adjacent to the shell membranes and acts as a seal. Thermostabilizing eggs is not common.

Egg weights.

Eggs are graded on the basis of size and quality. There are four general weight classes: extra large, large, medium, and small. The minimum net weights per dozen for eggs in these grades are respectively 27, 24, 21, and 18 ounces. In addition to these classes, two others occasionally are sold: i.e., jumbo (30 ounces per dozen) and peewee (15 ounces per dozen).

Both exterior and interior quality are used in determining the grade of an egg. Criteria used for this assessment include: shell condition and cleanliness, conformity and depth of air cell, clearness and firmness of white, and definition and shape of yolk. For these determinations, the interior of the egg is viewed by transmitted light, a process called candling.

Egg candling.

When eggs are candled by hand, the operator supports the egg between the thumb and index finger with the small end toward the palm of the hand. Then by a twist of the hand and wrist the egg is quickly rotated through a 180 {degree}

arc so that the contents are sent spinning. At that instant the large end is held before a candling lamp so that the light shines through and reveals the air cell and yolk, albumen, and shell conditions. Most commercial grading operations take place in cool, darkened rooms and hand candling is used only occasionally to check the accuracy of grading. Usually the quality of the egg is determined by mass scanning of several rows of eggs at a time as they move automatically over a light source that shines through them. During the same operation the eggs pass over tripping devices calibrated to sort them into various weight classes. Many types of automatic and semiautomatic candling and grading devices are available.

While most candling of eggs is done using incandescent light, the use of "black light," or ultraviolet candling, has proved valuable in detecting spoilage caused by the bacterium Pseudomonas, since many of these organisms produce a characteristic green or blue-green fluorescence when illuminated by ultraviolet light.

Grades.

Four edible grades of shell eggs are recognized: AA (or fresh fancy), A, B, and C. For AA grade eggs, the shell eggs must be clean, unbroken, of good even texture and strength, free from visible stains, discolorations, rough areas, or thin spots. The air cell must be 1/8 inch (3.2 millimetres) or less in depth, the white clear and firm, and the outline of the yolk only slightly defined and practically free of defects. In shelled eggs, egg white thickness is indicated numerically in Haugh units. When broken out, the egg must cover a small area, have a firm albumen, or thick white portion (72 Haugh units minimum), with much thick white surrounding a round and upstanding yolk. In A grade eggs, the air cell may be 3/16 inch (4.8 millimetres) in depth and the yolk fairly well defined; when such eggs are broken out, they cover a moderate area due to a medium amount of thin white present (60 Haugh units minimum). The shell of a B grade egg may be slightly faulty in texture or strength and slightly stained (not over 1/16 of the shell surface); the air cell may be as much as 3/8 inch (9.5 millimetres) in depth. The white may be slightly weak and the yolk outline well defined, slightly enlarged and flattened, and have defects not considered serious. The broken-out B grade egg covers a wide area. The yolk is flattened and enlarged and the albumen slightly weak (31 Haugh units minimum). C grade eggs may be moderately stained (less than 1/4 of the shell surface), misshapen, or faulty in texture or strength. The air cell may be over 3/8 inch in depth, bubbly or free moving. The white may be weak and watery and small blood clots or meat spots may be present. The yolk outline, which is plainly visible, shows that the yolk is enlarged or flattened; there may be germ development but no blood. When broken out, the egg covers a very wide area. There is no thick white (less than 31 Haugh units) but a very large amount of thin white and a very flat and enlarged yolk.

Substandard eggs.

In addition to these four salable grades of shell eggs, dirty and check eggs are permitted for use in egg products providing there is no leakage of the interior egg content; i.e., they may have moderate stains covering more than 1/4 of the shell surface or even prominent stains or adhering dirt and, with check eggs, the shell may be broken, but there must be an intact membrane (as demonstrated by candled appearance).

Eggs are designated as inedible if black-, white-, or mixed-rots are present. Also, moldy, musty, sour, or adulterated eggs are not permitted for sale as food nor are those with green or bloody whites or with stuck yolks, incubator rejects, or eggs containing embryo chicks at or beyond the blood ring condition, or any in such condition that washing and breaking result in contamination.

Shell colour.

The shell varies in colour from white to brown but colour does not affect the quality of the egg. A pigment imparted to the shell while the egg is in the oviduct is laid down in the spongy layer of the shell and is derived from the blood. Leghorn hens lay much whiter-shelled eggs than do most American classes. In some areas, white eggs are preferred, while in other regions, those with brown shells are chosen. Usually, more difficulty is experienced in detecting the interior quality of brown shelled eggs; small meat or bloodspots are harder for the candler to see at the packing station. White eggs and brown eggs may be colour sorted. When eggs with mixed shell colours are cartoned together, the consumer may have the erroneous impression that these lots are heterogeneous in other respects as well.

Packaging.

For retail use in the United States, eggs are repackaged in dozen and half-dozen paperboard cartons. In some other countries they are packed with straw or excelsior in long wooden boxes. In many parts of the world, they are marketed in baskets or boxes and the individual eggs are sold by weight. Several European countries stamp each egg with a date and number to meet the import restrictions of other nations.