Meyer lemon marmalade

I made this recipe for Meyer lemon marmalade from epicurious.com. The lemons are off of my salad citrus (four varieties grafted on one). I ended up using somewhat less sugar and yielding about 4.75 half pint jars. The stuff I was tasting as it was cooking was frighteningly bitter at one point. Then it cooked some more and the bitter moderated. When it says thinly slice, I don't think it means 1/4 inch rinds. Go smaller next time.

6 Meyer lemons (1 1/2 lb)
4 cups water
4 cups sugar

Special equipment:
Cheesecloth
Kitchen string
6 (1/2-pint) Mason-type jars, sterilized
Preparation
Halve lemons crosswise and remove seeds. Tie seeds in a cheesecloth bag. Quarter each lemon half and thinly slice. Combine with bag of seeds and water in a 5-quart nonreactive heavy pot and let mixture stand, covered, at room temperature 24 hours.

Bring lemon mixture to a boil over moderate heat. Reduce heat and simmer, uncovered, until reduced to 4 cups, about 45 minutes. Stir in sugar and boil over moderate heat, stirring occasionally and skimming off any foam, until a teaspoon of mixture dropped on a cold plate gels, about 15 minutes.

Ladle hot marmalade into jars, filling to within ‰ inch of top. Wipe rims with dampened cloth and seal jars with lids.

Put jars in a water-bath canner or on a rack set in a deep pot. Add enough hot water to cover jars by 1 inch and bring to a boil. Boil jars, covered, 5 minutes and transfer with tongs to a rack. Cool jars completely.

Cooks' note:
• Marmalade keeps, stored in a cool, dark place, up to 1 year.