Quality and Processing of Eggs and Egg Products

Eggs rank among the most nutritious and versatile foods available, delivering complete proteins alongside essential vitamins and minerals in a neat, natural package. But getting eggs from the hen to your kitchen in optimal condition requires careful attention to quality control, processing methods, and preservation techniques. Understanding how eggs are evaluated, processed, and transformed into various products reveals the sophisticated science behind this everyday food item.

What makes an egg high quality? 🔗

Egg quality encompasses both external and internal characteristics that determine consumer acceptability and functionality in food preparation. External quality focuses on the eggshell, including its strength, thickness, integrity, and cleanliness, while internal quality involves the properties of the albumen (egg white) and yolk. The quality of an egg begins declining immediately after laying, making prompt and proper handling essential.

Several measurable parameters help define egg quality. The Haugh unit measures albumen quality by assessing the height and spread of the thick white when the egg is broken onto a flat surface. Fresh eggs have thick, firm whites that stand tall, while older eggs display thinner, more watery whites. The air cell at the egg’s wide end provides another freshness indicator-it starts small in fresh eggs and grows larger as moisture evaporates through the porous shell over time.

Factors that influence egg quality 🔗

Egg quality is affected by both internal and external factors. Internal factors include genetic influences, the hen’s age, and stage of the laying cycle. External factors encompass nutrition, environmental conditions, management practices, and housing systems.

Genetics and breeding play fundamental roles in determining shell strength, albumen quality, and overall egg characteristics. Breeding companies have focused extensively on selecting for improved shell quality and laying performance. However, improving hen nutrition and carefully monitoring behavior are necessary to fully realize genetic potential.

Nutrition significantly impacts egg quality. Calcium and phosphorus balance is critical for proper egg production and shell quality. Layer rations typically contain 3.5 to 4% calcium and 0.35 to 0.40% phosphorus. An egg contains almost 2 grams of calcium, and since only 50 to 60% of dietary calcium is utilized in shell formation, hens require roughly 4 grams of calcium intake daily to maintain good shell quality.

Environmental conditions including temperature, humidity, and lighting must be carefully controlled. High ambient temperatures cause heat stress, leading to decreased egg production and compromised quality. As hens age, shell thickness typically declines because older hens produce larger eggs while being genetically limited in how much calcium they can deposit in the shell.

How shell eggs are processed 🔗

Commercial shell egg processing involves several systematic steps to ensure eggs reaching consumers meet quality and safety standards. Eggs destined for processing must be of high quality to avoid excessive yolk breakage during handling. Fresh eggs have thick whites and upstanding yolks, but over time the white thins and the yolk weakens. Consequently, eggs for processing are typically held in refrigerated storage no longer than seven to ten days.

Cleaning and washing 🔗

Eggs move along rollers into washing systems where brushes and pressurized water remove any shell contamination. They are then sanitized and receive a final rinse. Modern egg washers use pressure sprays, rotating brushes, and egg-spinning devices that increase contact between the egg and brush while minimizing damage.

Candling for quality inspection 🔗

Candling is an egg-grading process in which eggs are inspected before a penetrating light for signs of defects or freshness. Originally performed using candle flames, modern facilities now use high-intensity lamps or LED lights for consistent illumination.

During candling, inspectors can observe the air cell size and position, albumen clarity and thickness, yolk position and condition, and any visible shell cracks or imperfections. The air cell shrinks with age, making its size a good freshness indicator. Since older eggs have thinner albumen, the yolk rests closer to the shell and casts a sharper shadow. Hand candling or holding a shell egg directly in front of a light source is done to spot check and determine grading accuracy.

Grading and classification 🔗

USDA shell egg grading is a voluntary service paid for by shell egg producers. Eggs are categorized into one of three consumer grades. USDA Grade AA represents the freshest and highest quality eggs with clean shells and very firm, thick whites. USDA Grade A eggs are very high quality with reasonably firm whites. USDA Grade B eggs have thinner whites and are usually used for breaking stock or baking.

USDA quality grade standards define and measure quality based on shell appearance and condition as well as interior quality of the yolk and albumen. The final grade is based on whichever factor receives the lowest rating. Only eggs processed under USDA supervision are eligible for certification and the official grademark.

Preventing egg spoilage 🔗

Eggs are perishable products susceptible to quality deterioration when not properly stored. Several preservation methods help extend shelf life while maintaining quality.

Refrigeration and cold storage 🔗

Temperature control is the most common preservation method. Cold temperatures slow bacterial growth and the physicochemical changes that naturally occur in eggs. Eggs are stored at 4°C for short-term storage of two to three weeks with relative humidity of 60 to 70%. For longer storage up to six months, eggs can be held at -1.7° to -0.55°C with 70 to 80% relative humidity. Consistent temperatures are crucial, as fluctuations cause condensation on the shell, creating conditions favorable for bacterial growth.

Oil sealing and coating methods 🔗

Oil coating preserves internal quality, minimizes weight loss, and extends shelf life by at least three weeks longer than uncoated eggs stored at 25°C. The coating seals the porous eggshell, preventing moisture loss and reducing gas exchange. Oil-coated eggs maintained weight loss below 0.8% compared to 7.26% for uncoated eggs after five weeks of storage.

Under refrigerated storage, mineral oil coating extended shelf life by 10 additional weeks compared to uncoated eggs-15 weeks versus 5 weeks respectively. Various coating materials including mineral oil, vegetable oils, and wax can be applied, with soybean oil being a practical, cost-effective option.

Types of egg products 🔗

Beyond shell eggs, the industry produces numerous egg products offering extended shelf life and convenient applications for food manufacturers, foodservice operations, and consumers.

Liquid egg products 🔗

Liquid egg products are produced by breaking and separating eggs, then pasteurizing the contents. FSIS-approved automated equipment enables operators to break, separate, and monitor up to 162,000 eggs per hour. The liquid product is filtered to remove shell fragments and membranes, mixed for uniformity, and chilled before pasteurization.

Pasteurization uses specific time-temperature combinations depending on the product type. Pasteurized liquid egg products routinely contain less than 1,000 microorganisms per gram. Refrigerated liquid whole eggs and yolks must be maintained below 4.4°C, while whites can be kept at 7.2°C, with unopened shelf life of two to six days depending on microbial quality.

Frozen egg products 🔗

Frozen products are produced by filling containers with pasteurized chilled liquid egg and freezing in blast freezers at temperatures of -23.3° to -40°C. When thawed, frozen whole egg becomes quite fluid and easy to handle. However, frozen raw yolk develops a gelatinized consistency, so manufacturers often blend it with sugar, corn syrup, or salt at 2 to 10% levels before freezing to maintain fluidity when thawed. Frozen egg products have long shelf life when stored below -12.2°C.

Dried egg products 🔗

Dried egg products are typically produced by spray drying, though some egg white is dried on trays to produce flake or granular forms. Before drying egg whites, glucose is removed to produce products with excellent storage stability. Spray-dried egg white with glucose removed has an almost infinite shelf life when kept dry at room temperature.

Plain unstabilized whole egg solids have shelf life of about one month at room temperature and approximately one year when refrigerated. Stabilized products last even longer-up to one year at room temperature for whole egg and eight months for yolk solids.

Functional properties of eggs in food 🔗

Eggs are prized in food manufacturing not just for nutrition but for their remarkable functional properties. Eggs supply more than 20 functional properties including aeration, binding, coagulation, emulsification, foaming, and crystallization control.

Emulsification capabilities 🔗

Egg proteins have excellent emulsification properties and are commonly used in products like mayonnaise, dressings, and baked goods. Egg yolk is a complex emulsion itself, composed of 50% water, 32% lipids, and 16% protein. Of the lipids, 28% are phospholipids called lecithin.

The lecithin in egg yolk reduces surface tension between oil and water phases, minimizing the energy required to form stable emulsions. These amphiphilic molecules have both hydrophobic and hydrophilic ends, allowing them to bridge oil and water. Fresh liquid eggs, frozen eggs, and spray-dried products all retain emulsifying capacity, making them versatile ingredients for commercial applications.

Coagulation and thickening 🔗

Coagulation occurs when egg proteins transform from fluid to solid or semi-solid states. This property enables eggs to thicken custards, set quiches, and provide structure in baked goods. Heat causes protein denaturation, and once coagulated, egg proteins do not return to their original fluid state.

Egg white proteins are responsible for gel structures in products like baked custard and contribute to the thickening of stirred custards. The beneficial characteristic relates to denaturation and coagulation at particular temperatures, forming stable matrices that improve texture and structure in countless food applications.

What do you think? How might consumer preferences for cage-free or organic eggs impact processing practices and quality standards in the future? And with plant-based egg alternatives gaining market share, what unique functional properties might be hardest to replicate without real eggs?

References

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