Most store-bought eggs in the United States come from large commercial laying operations, where hens produce eggs that are collected, washed, graded, and packaged before being shipped to grocery stores. The entire process from hen to shelf typically takes one to three weeks, with federal regulations governing every stage from the laying house to the refrigerated display case.
Inside a Commercial Laying Operation
The vast majority of eggs on grocery shelves come from farms housing thousands to millions of hens. These operations fall into two main categories. Conventional farms keep hens in enclosed housing systems, while cage-free or free-range farms give birds varying degrees of space and outdoor access. Regardless of the housing system, eggs are collected either through automated in-line systems, where eggs roll onto conveyor belts directly from the laying area into a processing facility on the same property, or through off-line systems, where eggs are packed into flats and trucked to a separate processing plant.
Hens typically begin laying around 18 to 20 weeks of age and produce roughly one egg per day at peak production. The eggs you see labeled “cage-free,” “free-range,” or “pasture-raised” all come from commercial operations, but the hens’ living conditions differ. What doesn’t change is the processing that happens after the egg leaves the hen.
How Eggs Are Washed and Graded
Unlike many countries, the United States requires commercial eggs to be washed before sale. This removes the natural protective coating on the shell, which is why American eggs must be refrigerated. Federal regulations set specific standards for this process: wash water must be at least 90°F and at least 20°F warmer than the egg’s internal temperature. This pressure differential prevents bacteria from being drawn inward through the shell’s pores. Only potable water with approved cleaning compounds is used, and the water is changed at least every four hours.
After washing, eggs pass through a sanitizing spray rinse containing chlorine. They’re then dried before moving to the grading stage.
Grading happens through a process called candling, where a bright light shines through each egg so inspectors or automated equipment can check for interior quality, including the size and position of the yolk, the clarity of the white, and the size of the air cell at the wide end. The grading room is kept dark so these details are easier to see. Each egg is individually evaluated and sorted into grades: AA, A, or B. Most grocery store eggs are Grade A, meaning they have a firm white, a round yolk, and a clean, uncracked shell. A USDA grader or quality assurance inspector must supervise the process for any eggs carrying the official USDA grademark on the carton.
After grading, eggs are sorted by size (from peewee to jumbo, based on weight per dozen) and packed into cartons.
Salmonella Prevention at the Farm Level
The FDA’s Egg Safety Rule puts specific requirements on farms with 3,000 or more laying hens to prevent salmonella contamination before eggs ever reach the processing plant. Farmers must test the environment in each poultry house when hens reach 40 to 45 weeks of age. If a flock is molted (a practice where feed is adjusted to restart the laying cycle), additional testing is required four to six weeks after each molt ends.
When environmental tests come back positive, the farm faces a choice: divert all eggs from that flock to pasteurization for the rest of the flock’s life, or conduct four rounds of direct egg testing at two-week intervals. This layered testing system is designed to catch contamination at the source rather than relying solely on processing to make eggs safe.
Once eggs are at least 36 hours old, they must be held and transported at no more than 45°F. That cold chain continues from the farm through the distribution center to the grocery store’s refrigerated case.
What Makes “Specialty” Eggs Different
Eggs labeled as omega-3 enriched, vitamin-enhanced, or vegetarian-fed come from the same type of commercial operations. The difference is what the hens eat. For omega-3 eggs, producers add ground flaxseed to the feed. Flaxseed is rich in a plant-based omega-3 fatty acid, and hens that eat it produce eggs with significantly more omega-3s in the yolk. A standard egg contains about 173 milligrams of total omega-3 fatty acids, while an egg from a hen fed 15% flaxseed in her diet can contain around 468 milligrams.
The conversion isn’t especially efficient. Hens convert less than 6% of the plant omega-3 from flaxseed into the forms most beneficial to humans (the same types found in fish oil). Still, the enrichment roughly doubles or triples the omega-3 content compared to a conventional egg. “Vegetarian-fed” simply means the hens’ feed contained no animal byproducts, which is a feed choice, not a housing one.
From Packing Plant to Store Shelf
After grading and packaging, cartons are stamped with a pack date (a three-digit number representing the day of the year, so 032 means February 1st) and often a sell-by or expiration date. Eggs are then stored in refrigerated coolers at the plant before being loaded onto refrigerated trucks for distribution.
Most eggs reach grocery stores within a few days of packing, though regulations allow sell-by dates up to 30 days after the pack date depending on the state. The pack date is the most reliable indicator of freshness. An egg carton with a pack date of 045 and a sell-by date 30 days later could sit on shelves for roughly a month after it was packed, and the eggs themselves may have been laid a few days before packing.
By the time you pick up a carton, those eggs have been collected from a laying house, washed in warm sanitized water, candled under bright lights in a dark room, sorted by size and quality, packed into cartons, kept at 45°F or below, and trucked to your local store. The entire system is designed to deliver a clean, graded, refrigerated product, which is also why store-bought eggs in the U.S. must stay refrigerated at home. Without their natural coating, the shell is more porous, and cold storage is what keeps bacteria from growing.