The difference between peeling farm fresh and, market fresh eggs
Sometimes, not always, it can be challenging to peel farm fresh eggs. This is because in some (not all) farm fresh eggs the albumen (the white) has an acidic environment and the pH is somewhere between 7.6-7.9 and, the naturally occurring carbon dioxide trapped inside the egg causes the albumen (the white) to push and stick to the 2 inner shell membranes. Research (Link) suggests that the inner membrane of the egg could be helpful in fighting global warming due to it's ability to absorb carbon dioxide.
Why is carbon dioxide trapped inside an unwashed farm fresh egg?
When a hen lays her egg there is a very thin, clear, shiny membrane that coats the outside of the egg as it comes out. If you touch this membrane as soon as the egg is laid, it's warm and feels a bit sticky. As the egg cools (after a few seconds), the membrane is very difficult to see. This membrane is there to protect the egg from contamination. Egg shells are very porous and bad bacteria can enter a porous shell. Remember, hens lay eggs with the intent of hatching baby chicks and they want as many eggs to hatch as possible. This membrane is nature's way of protecting the integrity of the egg.
Why eggs from farmers market, health & grocery stores peel better
Eggs from the grocery store, farmer's market and health food stores have an expiration date of 30 days from date of packaging. Eggs sold to the general public must be (food safety laws and regulations) be washed and sanitized, and this removes the outer protective membrane which makes the egg shell extremely porous. This is why those same eggs are then coated with a USDA approved oil or foam (page 9, section 5 (D).
After the outer protective membrane is washed off the egg shell, the egg is highly porous and air penetrates the shell. This causes some of the natural carbon dioxide in the egg to be released through the open pores of the shell. First, this process reduces the acidity of the egg, secondly, when the acidity is lowered, it causes the pH to increase to about 9.2 (depending on temperatures and humidity). Thirdly. When the pH increases, the air pocket between, (a) the egg shell, (b) the 2 connected inner membranes and, (c) the albumen; get bigger and creates an environment for separation. Making the egg easier to peel.
Sanitation example: Several quaternary ammonium compounds are approved for use as a sanitizing agent. Instructions to convert titration kit results to the equivalent concentration of active chlorine in the solution must be provided. The manufacturer of the test kit is usually the best source of the equivalency table. Source Link to USDA Egg Handling Handbook