The importance is the total weight of fruit, but I recommend using only 1 or 2 lemons since they are a bit trickier to zest and section.
Many traditional marmalade recipes have you remove all the peel, boil it a time or two, and then separate the zest from the pith. I've tried that method. I find it messier, more complicated, and less flavorful than simply taking a bit of time to carefully zest the fruit, remove the pith, and then cut out peel and membrane-free sections of oranges.
- 5 pounds ripe oranges, grapefruit, and lemons
- 6 cups sugar
- 3 pint jars with sealable lids
- Wash and dry the fruit. Use a sharp vegetable peeler or paring knife, remove the brightly colored zest – and only the brightly colored zest – from the oranges. Be sure to leave behind any and all of the white pith directly underneath, it is very fruit. Chop the resulting zest – bigger pieces for chunkier marmalade, ribbon-like strips for a more spreadable result. Set zest aside.
- Cut the ends off the zested fruit and then, working with one piece of fruit at a time, cut off the thick white pith from each. Working over a bowl to catch the juices, hold a fully peeled citrus fruit and use a sharp knife to cut out each section from the membrane holding the sections together. See How to Section Citrus for pictures if you've never done this before.
- Squeeze any juice out of the membrane once you've cut out all the fruit. Set the membrane aside, along with any seeds – the pectin in these will help "set" the marmalade later.
- Combine the zest, fruit, juice, 4 cups of water, and sugar in a large heavy pot and bring to a boil.
- Meanwhile, lay a double layer of cheesecloth in a medium bowl and put membranes and seeds in the bowl. Lift up the corners and tie the cheesecloth into a bag to hold the membranes and seeds. Add this "pectin bag" to the pot.
- While the mixture comes to a boil, put a canning kettle full of water on to boil if you're planning to can the marmalade. In any case, put a few small plates in the freezer to chill them. When canning kettle water boils, use it to sterilize the jars and lids.
- Bring marmalade to 220°F and hold it there for 5 minutes. Be patient, this can take quite awhile. Put a dollop of the mixture on a chilled plate, swirl the plate to spread the mixture a bit, and drag your finger through the mixture. A "set" mixture will hold a clean track behind your finger.
- Remove "pectin bag", squeezing any marmalade in it out and back into the pot before discarding the bag. Take marmalade off the heat and let sit 5 minutes. Set up clean jars next to the pot.
- Stir marmalade to distribute the zest evenly in the mixture. Use a ladle to transfer the marmalade into the jars, leaving 1/2 inch of headspace at the top of each jar. Put lids on the jars.
- If you're canning the marmalade, put the jars in the canning kettle and boil for 10 minutes. In any case, let jars cool to room temperature before putting in a cool dry cupboard (if you've hot water processed them) or the fridge (if you didn't hot water process).
Marmalade will keep a really long time. It is all sugar. Opened marmalade needs to be in the fridge, but unless you use a dirty spoon in the jar, it seems to last for approximately forever, although officially people say 6 to 12 months.