You begin with a large purchase of boneless, skinless chicken breasts. You can do this with chicken on the bones, but it's much more work. You have to weigh out the cost of one way versus the other for yourself. I personally like the ease of boneless, skinless chicken. If I were really on a tight budget, I'd do the work on the bone-in chicken to save money, but there would be less yield.
Needed:
Large crock pot (cut everything in half for a smaller crock pot)
Chicken, fresh or frozen, either works, enough to fill up the crock pot (probably 6-10 lbs., depending on your crock pot)
1 cup water
2-cup measuring cup
Quart
freezer Ziploc (or equivalent) bags
Permanent marker
(Optional) 1 carrot, 1 celery stalk, and 1/2 onion, chopped, if you desire
(Optional) Salt, if desired, to taste
First thing in the morning, fill the crock pot with chicken as full as you can while still being able to close the lid properly with a little room for seasonings if you choose to use them. If adding salt (optional), mix it into the water and then add. Cover. Set on HIGH for the first 2 hours. Turn to LOW after that and let the chicken cook until evening. Once the chicken is done, turn off crock pot and drain chicken in a colander. Catch the liquids if you want to use them as chicken broth. (For broth, strain liquids, cool a bit on the counter, then let cool overnight in fridge. Skim off fat and freeze in 1 or 2 cup increments, or in whatever increments you find useful.)
Put chicken in a large bowl to cool before shredding. Once cooled, sit yourself in a comfortable place (I sit at the dining room table) and begin pulling the chicken apart in shreds, keeping all chicken inside of bowl (shredded and non). Remove bones and gristle at this point if you're using bone-in chicken. Take great care to remove all bones.
Once it is all shredded, label at least 5-8 freezer bags with something like "2 cups cooked chicken". Begin measuring chicken into the 2-cup measuring cup and fill each bag with 2 cups of chicken shreds
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Zip the bags closed and remove as much air as you can. Put in the freezer and you are done! (except for clean-up)