Sometimes the thriftiest tips are right at my fingertips and I don't think to pass them on. Such is the case with eggshells. I feed my chickens their own eggshells instead of purchasing pricey Oyster Shell supplements. I do keep some Oyster Shell on hand in case I run out of egg shells, but I much prefer to use eggshells when possible. Hens need calcium to make an egg with a nice strong shell. Eggshells have lots of calcium.
Every few weeks I clean out the back egg stash and cook the eggs for the chickens. Then I wash and prep the shells to use as a supplement. The whole process only takes a few minutes of work....although there is some setting time. I've been doing this for years and in that time I've seen it done many ways. This is the method I prefer:
Rinse the egg shells thoroughly. I rub my fingers inside them to make sure any remaining egg white is removed. Drain and place on a baking sheet. I put my oven on the lowest setting (170) and set it to convect (this runs the fan. If you don't have this setting it's ok) Put the baking sheet in the oven and leave it for about 30 minutes. After 30 minutes, turn the oven off but keep it closed. I usually just walk away at this point and go about my day, letting the oven gradually cool down. Wait at least another 1/2 hour. You want to dry them out without burning them (don't use the broil feature...it gets ugly, I promise!)
After they cool I simply crush them in my hands. You may choose to use a mortar and pestle or a rolling pin. A bowl and an ice cream scoop? Mallet? Whatever....just get them on the smallish side. Do NOT pulverize them, do not use a grinder! If the pieces are teeny tiny, the calcium doesn't absorb as readily.
You may notice pieces of dried membrane that came off during the crushing process. I usually go outside to transfer them to a container at this point. I shake them pretty good to get those pieces to float away. It's not a problem if you don't, but it can get all over the counter if you do it inside. I store my eggshells in a mason jar until I need them.
Chickens should be given eggshells as a supplement in a separate bowl from their feed so they can choose how much they want. Do not mix it in with the feed. Roosters and pullets that haven't begun to lay yet don't need the calcium and it can actually harm their kidneys.
Pretty simple, right? Stored correctly and they will keep for several months which is especially helpful when egg production falls off and not as many eggshells are available to make more. I try to stock up when I can and never feed commercial eggshells to your flock. Eggshells from another source may contain bacteria that your flock isn't used to and might actually make them sick. If your hens own eggshells aren't available definitely turn to commercial oyster shell supplements which don't have this risk. Have fun baking!