1. Rinse the apples and cut them coarsely into chunks, then put them and the cores and seeds, into a very large stockpot.
2. Add the water, cover, and bring to a boil. When bubbling, reduce the heat a bit, leave the lid askew, and cook for 20 to 30 minutes, until the apples are tender and cooked through.
3. Line a mesh colander with a piece of muslin cloth or a few folds of cheesecloth (or use a jelly bag and stand) and set it over a deep bowl, then ladle the apples and the liquid into the colanders. (I used two lined colanders since it was quite a bit of apples.)
4. Let stand overnight (or at least three hours), and no matter how tempting, do not press down at any time on the apples to extract more juice or the jelly will get cloudy.
5. The next day, measure out the juice. (See Note below about the apples.) You should have 8 cups (2l). Pour it into a stockpot fitted with a candy thermometer, add the sugar and lemon juice, and bring to a boil. During cooking, if any white scum rises to the surface, skim it off.
6. Cook until the temperature reaches 220ºF (104ºC). At that point, turn off the heat and begin testing the jelly on a chilled plate in the freezer, using the method mentioned in the headnote. When it wrinkles and holds its shape, it’s done. If not, continue to cook and re-test it at intervals. This batch set at 230ºF (110ºC).
7. Remove from heat, stir in the liquor, and ladle into clean jars, then cap tightly.