I found this site today and found it very interesting!! Here is the link
Here is what it says about canning butter
Canning butter at home is easy and inexpensive. Anyone who can boil water has all the skills necessary to preserve butter at home. You need a few supplies first:
Canning jars, lids & bands (from the store)
Good Quality Fresh Butter, with salt added
First get your canning jars. I use small wide-mouth jars that hold 8-oz each. You can buy them at Walmart or get them from you great Aunt Matilda, or you may have some around the house already. Do not use mayonnaise jars or peanut butter jars. You want real canning jars. Depending on how much butter you think you will be able to use before it spoils, you may choose from a variety of jar sizes. The smallest are 4-ounce, and will hold 1 stick of butter. 8-ounce jars will hold 2 sticks of butter and pint or 16-ounce jars will hold 1 pound of butter. I prefer to use 4 and 8-ounce jars for canning butter. This is a reasonable amount for me to use up after I've opened up the jar.
Now, wash all of your canning jars and lids and bands. If you buy the jars at the store, they come with lids and bands. If you get them from Aunt Matilda, then go to the store and buy new lids and bands.
Allow the jars to air dry.
Bring a big pot of water to a boil. Place the canning jars inside the pot and let them come to a boil with the water. Allow each jar to become totally immersed in the boiling water for about a minute. Use your tongs to remove the jars and set them on a clean dishcloth, upside down, to dry. Continue until all of your jars have been boiled. Now turn off the flame under the boiling pot. Gently slip the lids and bands into the almost boiling water. Allow them to sit for a bit and then take them out with the tongs and put them on the dish cloth next to the jars.
Now, in the medium sized pot melt your butter. Unwrap all of the butter that you wish to preserve. Each pound of butter will fill two 8-ounce jars. Each stick of butter will fill one 4-ounce jar. I usually process 4 pounds at a time. Heat the butter over medium low. Allow it to melt and bubble gently. The butter will foam on top, that is normal. Simmer the butter for 5 to 10 minutes to get rid of any excess moisture.
Dip the ladle & funnel into the hot water to make sure they are sterile. Allow them to air dry. Place the funnel into a jar. Ladle up the butter into jar, until it's mostly full. Do not overfill. You want about 1/2-inch of empty space at the top of each jar. Go on to the next jar and fill it the same way. Continue until all of your jars are full and your butter is used up.
Now place a lid and a band on each jar. Screw them down firmly, but not overly tight. Allow the jars to sit overnight. They will seal automatically and the butter will harden. If you get a chance, shake the butter briskly while it's cooling, to emulsify it and make it creamy. This isn't necessary, but it makes the butter pretty.
Store your butter in a cool place, preferably not close to the stove. I've heard that it will keep for 3 years this way, but I would stick with 2 years to be on the safe side. Be sure to label and date the jars with a permanent marker.
Because of the cost and time invested in canned butter, I prefer to use it solely as a spread. For all baking and even seasoning vegetables I use butter flavored shortening. This makes the butter last a lot longer.