Wash your jars and lids in warm, soapy water and rinse well. Place the jar rack into the pressure canner, set the clean jars in the canner, add water to the jars and fill canner to around 3-inches. Cover and boil jars for 10 minutes to sterilize. Warm your lids in a small pot of water over low heat. Keep jars and lids warm until they are ready to use.
Remove the beef stock from the refrigerator and skim off the fat that has risen to the top.
Return the stock to a large saucepot and bring to a boil over medium-high heat.
Spread a kitchen towel on the counter. Remove the warm jars from the canner using your jar lifter, drain, and line up on the towel.
Use the canning funnel and ladle and fill the jars with beef stock, leaving 1-inch headspace at the top of the jars.
Use your magnetic lid lifter to lift lids out of the warm water, center lid on the jar, and screw on band until it is fingertip tight.
Place the jars into pressure canner on the canning rack. Leave space in between the jars. Once the jars are all in canner, adjust the water level per your pressure canner's instructions. If adding water, use the hot water from the small pot you used to warm your lids.
Place the lid on the canner and lock it. Bring the canner to a boil over medium-high heat. Follow the directions for your pressure canner and vent steam for 10 minutes, add the pressure weight. Bring the canner to 10 pounds of pressure, and process pint jars for 20 minutes and quart jars for 25 minutes at altitudes of less than 1,000 ft. Adjust processing time for your altitude if necessary.
When processing time is complete, turn off the heat and allow the pressure canner to cool naturally until it reaches 0 pressure, about an hour.
Spread a kitchen towel on the counter and check the jars. Unlock the cover of the canner, and remove it by tilting the lid away from you so that steam does not burn your face. If jars are still boiling, let them sit in the canner for another 5 minutes, or until the boiling stops.
Use a jar lifter to lift jars carefully from canner and place on a kitchen towel. Let the jars cool for 12 to 24-hours. You should hear a "ping" as the jar lids seal.
After 12 to 24-hours, check to be sure the lids have sealed by pushing on the center. The lid should not pop back up. If the lid flexes up and down, it did not seal. Refrigerate the jar and use up within a few days or freeze for longer.
Once the jars are cool, remove the screw on bands and wash the jars. Label and date the jars. Store your jars in a cool, dark place and use within 12 months. Yields about 8 pints or 4 quarts depending on how long you cooked the stock.