Thin-skinned, sweet-tart, and about the size of the top portion of your thumb, kumquats are the kind of rare citrus fruit that you can eat whole. They’re actually not citrus at all—a technicality that I’ll leave to botanists—but they share so many properties with lemon and orange that it makes sense to lump them all together when considering what makes a good marmalade.
A few words on sugar: I know it’s all the rage to avoid it, but sugar can be incredibly important when making preserves. It inhibits microbial growth, enabling preserves made with sugar to last a lot longer in the refrigerator than preserves made with little or no sugar. Because there is only so much kumquat marmalade one can eat in a day, I wanted a preserve that would keep in the refrigerator for a while without going moldy.
But because the sweetness levels vary so much with kumquats, I provided a recipe with a range in how much sugar to add. The kumquats I had were quite sweet, so I really didn't need the extra 1/4 cup of sugar. Yet these were peak-season fruit. I'd guess that earlier in the season, I might have needed more sugar. If you like honey, a touch of honey (2 tablespoons, say) added at the end would also be a nice way to give the marmalade a rounded sweetness that would pair well with rich cheeses or yogurt.
Makes 4 cups
- 908 grams / 2 pound kumquats
- 350-400 grams / 1 3/4 cups to 2 cups granulated sugar
- 2 lemons
- Pinch of fine sea salt
- 2 cups water
Remove the stem ends and cut the kumquats in half lengthwise, picking out the seeds where visible (It’s OK if you don’t get all the seeds. They can be picked out of the preserve as it simmers, too.)
Place the kumquats in a pot, cover with water, and bring to a boil. Drain and rinse under cold water. (This process removes some bitterness from the pith.)
In a bowl, combine the kumquats, 350 grams / 1 3/4 cups sugar, the juice of 1 lemon, and a pinch of salt. Cover and refrigerate overnight or up to 5 days.
Put the marmalade in a pot and add the water. Bring to a boil and then lower to a simmer. Cook until the syrup thickens and the fruit starts to turn translucent around the edges, about 30 minutes.
As you cook the marmalade, taste it. If it tastes very tart, add anther 50 grams / 1/4 cup sugar. If it tastes too sweet or you want to balance the flavor with acidity, squeeze in the second lemon.
The marmalade is finished with the syrup coats the back of a spoon convincingly. At this point, any seeds that weren’t removed before should be easy to see. Pick them out and discard. Cool the marmalade to a warm room temperature.
Remove about 1/3 of the marmalade and puree in a food processor. Mix into the remaining marmalade. Store in clean jars or plastic containers (you will have about a generous quart of marmalade). This marmalade keeps in the refrigerator for up to 2 months. Alternatively, freeze some of the marmalade for up to 4 months.