4 pounds Granny Smith apples
8 cups water
Stem the apples and coarsely chop them. Place pieces in a heavy, non-reactive 5-quart pan; include seeds, skins and cores. Pour in 8 cups water. Bring to a boil, reduce heat to a simmer and cook, partly covered, for 30 minutes. Stir the pan once or twice, turning the apples at the top into the simmering liquid.
Strain mixture through a damp cheesecloth-lined sieve for 1 hour. There will be about 8 cups of apple juice. Begin to reduce this juice in a 5-quart pan while continuing the straining process for another hour. The last cup of juice has a higher pectin level than the juices strained initially. Add this late juice to the juices reducing in the pan. Reduce to 3 cups total.
If you are going to use the stock within the next 2 weeks, simply pour it into a clean storage jar and refrigerate. Stock can also be frozen in clean plastic containers.
To vacuum-seal the stock, fill hot, sterilized jars to within 1/4 inch of the lips. Wipe the rims clean =, attach new lids and screw caps on tightly. Invert jars briefly to vacuum seal, or process in a boiling water bath, submerged by 1 inch, for 10 minutes.