The egg is called nature’s ideal food and readily consumed in many parts of the world. Though many animal species lay eggs, chicken eggs are most commonly consumed. Today, quality of the egg is important from several standpoints. So, egg grading is necessary.Egg grading involves sorting of eggs according to quality, size, shape, weight and other factors. Food quality is the characteristics of the food product that is acceptable or rejected by the consumer. Quality of eggs is determined by both internal and external quality standards. External factors include shell structure, color, shape, and texture of eggs. Internal quality includes air cells, egg white, egg yolk etc.
Some tests like sniff test, visual inspection, floating test, candling are done to check whether eggs are of good quality or not. Candling is the most used industrial method.
How to do candling?
Hold the large end of the egg between thumb and first two fingers in the candle-light in the slanting position and observe the shell structure, air cells, egg white, and yolk.
Let’s get into how eggs are graded according to their external & internal qualities:
External egg quality
External egg quality is determined by its shell, texture, color, shape, and soundness. The eggshell should be clean, unbroken, and smooth. Surface cracks on the shell are easier to detect during handling. Poor eggshell quality is undesired and causes losses. Total quality management, GMP should be implemented throughout egg production cycle for good eggshell quality. The eggs should be uniform in color, size, and shape.
It is surprising that eggs are not sized individually but sized by combined weight of one dozen eggs. According to weights eggs are classified as:
|Size or weight class||Minimum net weight per dozen|
|Extra large||27 Ounces|
Internal examination of an egg is done by candling which evaluate the egg white, yolk, and air cells.
Air Cells – Depth of air cells determine its quality. It is the distance from top to its bottom when the egg is held with the air cell up. The air cell is small, not more than 1/8 inch deep in fresh egg; with time because of evaporation air cell becomes larger and egg quality downgraded.
Egg yolk – Fresh and good quality egg yolk is surrounded by a dense layer of albumen or white. So, while candling it moves slightly away from the center and yolk outline is only slightly defined. With ages deterioration occurs, albumen thins, yolk become more visible during candling and tends to move freely.
Egg white – The egg white is composed of four structures. First is the chalaziferous layer surrounded by egg yolk. Second is the thin layer, the third layer is thick & firm which holds the inner white and yolk. Final outer thin layer lies inside the shell membranes. The egg white or albumen characteristic is determined by egg yolks behavior during candling. The fresh egg has firm, thick and clear white. With ages it becomes weak and watery; CO2 loss causes the albumen to become transparent.
Spots – Eggs with blood or meat spots more than 1/8 inch diameter are inedible. Very small pinpoints spots should not be considered. Chalaza, which helps to hold the yolk in the center looks like spots. One should not confuse with this.
According to United States Department of Agriculture (USDA), eggs are graded based on its quality into AA, A, and B.
Grade AA – Eggs have clean, un-cracked shell, thick & firm white, round & centered yolk free from defects. They are best for frying and where appearance is important.
Grade A – Egg white is reasonably firm, air cells are quite large and other characteristics are similar to grade AA eggs. They are mostly sold in stores
Grade B – egg shells are unbroken but have slight stains, thinner egg white, larger and flattened egg yolk with a well-defined outline. They are mostly used for bakery and other commercial operations.
USDA Grade standards chart | Egg Grades
How to improve egg quality
Egg quality can be improved by following methods:
- Washing promptly – use water with the iron content of less than 2ppm.
- Low-temperature preservation – ideal 50-600 F
- Shell treatment – using oil, whey protein concentrate as coating layer
- Thermostabilization – eggs are immersed in water at 49°C for 35 minutes or 54°C for 15 minutes or 56°C for 10 minutes or 60°C for 5 minutes to stabilize the thick albumen
- Controlled humidity – ideally 70% RH
- Overwrapping – Films like polyethylene, cellophane, are used.