Cutting away all the pith looks like the obvious cure for a bitter grapefruit marmalade, and it overshoots. Grapefruit marmalade is bitter mainly because of naringin, a compound concentrated in the peel and pith, but that same white pith holds most of the fruit's pectin, so makers trim it rather than strip it.
What makes grapefruit marmalade bitter?
Naringin is the main culprit. It's a flavanone, one of the citrus flavonoids, and it tastes bitter; its close relative narirutin is tasteless. When researchers in Iran and Spain compared a bitter Duncan grapefruit with a Thomson navel orange and a Wase mandarin in a 2019 study, the grapefruit carried more naringin than either of the sweeter fruits.
Those compounds aren't spread evenly through the fruit. The same paper notes that the albedo (botanists' name for the pith) has been found in several citrus species to hold significantly higher flavonoid levels than other tissues. Unlike juice, marmalade keeps the peel, and that is where those flavonoids concentrate.
Why not just remove the pith?
Because the pith also sets the jar. The National Center for Home Food Preservation's citrus marmalade recipe instructs cooks to include a bit of the membrane under the skin, since the pectin is concentrated there. Take the pith out and the bitterness goes with it, but so does much of what makes the jar gel.
Grapefruit is already at a disadvantage there. Lemons gel when sugar is all you add, while grapefruit, like oranges, is low enough in natural acid or pectin that the cook may have to add one or the other; the NCHFP's pectin and acid chart puts lemons in Group I and grapefruit in Group II. Strip out the pith and leave out lemon, and the set has little to work with.
And there's a lot of pith. Grapefruits have a thick rind, as the Paris-based pastry chef David Lebovitz notes in his pink grapefruit marmalade, so the bitter layer and the setting layer are the same tissue.
How makers handle grapefruit's bitterness
Published recipes mix and match a few moves.
- Use peel from only some of the fruit. Both of Lebovitz's grapefruit recipes use the rind of half the grapefruit. In the pink version he scoops the pulp from four of eight halves and slices only the other four; in his grapefruit vermouth marmalade he peels two of four fruit down to the flesh and cuts strips from the other two rinds.
- Pre-cook the peel and throw out the water. Lebovitz simmers his sliced grapefruit for 5 minutes, lets it stand in the hot water until translucent, then drains it and discards the liquid, and some of the bitterness goes with it.
- Add lemon. Lebovitz adds the juice of a lemon to his pink grapefruit batch. The NCHFP recipe builds in lemon peel next to the grapefruit and orange. Lemon brings the acid and pectin grapefruit is short on.
Ripeness helps too. In a 1985 study of Duncan grapefruit in Plant Physiology, University of South Florida researchers found that naringin concentration in the fruit fell as it matured, because the fruit grew faster than the naringin did; the 2019 study also saw flavonoids drop through ripening. On that evidence, fully mature fruit carries less naringin per spoonful. We've written more on how tree-ripening shapes a marmalade.
Duncan and Melogold, old grapefruit and new
Variety sets the starting point before any technique. Of our eight marmalades, Duncan is the most bitter and Melogold sits sixth, milder than Duncan or our Eureka lemon.
The Duncan is the old one. UC Riverside's Citrus Variety Collection says it is believed to be the oldest grapefruit variety in American cultivation: it arose around 1830 near Safety Harbor in Florida and was named and introduced about 1892. It is seedy, with a flavor the collection's evaluators called "rich, fruity, intense." Our Duncan Grapefruit Marmalade finishes with gentle tannin and a maraschino cherry note at the finish.
Melogold is the modern answer to grapefruit bitterness. UC Riverside breeders released it in 1986, crossing an acidless pummelo with a seedy, tetraploid Marsh grapefruit, and the collection's notes describe a seedless fruit whose acidity runs "much lower than 'Marsh'" all season, with a mild, sweet flavor closer to pummelo than grapefruit. It may show a slight bitterness early and late in its season. We make our Melogold Grapefruit Marmalade for anyone who has written grapefruit off as too sharp.
Both labels read the same way, with citric acid added to the fruit, cane sugar and water. Neither lists added pectin. Each Duncan and Melogold jar carries our standard grapefruit note, which asks anyone who avoids grapefruit for medical or dietary reasons, such as a medication, to check with their doctor first.
Putting the bitterness to work
In our cheese pairing guide, Duncan or Melogold goes up against gorgonzola, stilton or roquefort, the boldest pairing on the board, where the salt and fat stand up to the bitterness. A sharp cheddar or a spicy salami handles it as well. In drinks, a teaspoon of grapefruit marmalade stirred into 2 oz of gin and topped with ice and soda makes a long, dry highball, and Duncan's bitterness works against the sweetness of bourbon in a sour.
Photo by Alina Nichepurenko on Unsplash.
