Before storing the stock, you need to skim as much of the fat as you can. It is helpful if you skim fat while cooking so you don’t have as much after it’s done simmering. If you do have fat left still (like the example in the photo above), you should cool the stock in the fridge before portioning for freezing. When it cools, you can more easily skim/remove the fat from the top.
After the stock has cooled and the excess fat removed, it is time to portion for freezing. I find that most recipes I prepare that require chicken stock (aside from soups) require portions of about a half a cup. So I have found that freezing stock in 1/4 cup portions allows me some easy flexibility with quantities as needed, whether my recipe calls for increments of quarter cups, half cups, or even whole cups.
I use these silicon cupcake/baking pans from Amazon to freeze the stock. Silicon works well because it is easy to remove the stock from them after freezing, and it is also easy to clean. The baking cups hold about 1/3 cup of liquid, but I measure out 1/4 cup scoops into each for more convenient portioning. Each silicon tray of 12 cups will provide for a total of three cups of frozen chicken stock, frozen into 1/4 cup increments.
I personally own two of the trays, which means I have to freeze them in batches. While one batch is freezing, I keep the remainder of the chicken stock covered in the refrigerator.
After pouring 1/4 cup of stock into each cup, transfer the silicon baking tray to the freezer.
Tip for transferring silicon trays full of liquid from the counter to the freezer: Since the silicon is flexible, it can easily spill if not moved carefully. I find that a plastic cutting board (or anything rigid and flat) slipped under the silicon tray allows me to move the tray without spilling the liquid. I then slide the tray off of the cutting board into the freezer.
After the chicken stock has frozen completely, the portions can be easily popped out of the silicon baking cups by pressing from the bottom to invert each cup and pop the frozen stock portion out.
Place the frozen portions in a large freezer bag labeled with the date the stock was made (as Martha recommends that frozen stock be stored in the freezer for up to three months).