Florida Grapefruit Pie

the Gulf coast cousin of the Key lime pie: grapefruit juice and zest set with condensed milk and yolks in a graham crust, with segments folded through for texture

Origin: Florida, United States

From the journey of Grapefruit.

Florida's citrus pies all descend from one nineteenth-century discovery: that the acid in citrus juice will thicken sweetened condensed milk without any heat at all. The proteins in the milk coagulate on contact with acid in the same way they would in a cooked custard, which meant that a household with no reliable oven, no fresh milk, and no ice could still produce a set dessert. That is why the Key lime pie exists, and the grapefruit pie is the same idea applied to the fruit the Gulf coast actually grew. The difficulty is that grapefruit juice is markedly less acidic than lime juice, so a straight substitution gives a pie that never sets properly. The fix used along the coast is to reduce the juice first, which concentrates both the acid and the flavour, and to bake the filling briefly rather than relying on the acid alone. Reduction also solves a second problem: grapefruit juice carries a great deal of water, and unreduced it dilutes the filling into something bland. The folded segments are what distinguish this from a simple citrus custard. Cut free of their membranes and drained, they keep their shape in the set filling and give the pie a fresh, faintly bitter interruption against the sweetness of the condensed milk, which is otherwise considerable. Pink or ruby fruit gives a pale blush that survives baking; white grapefruit gives more bitterness and a better balance.

Ingredients

Crust

  • 200 g digestive biscuits or graham crackers, crushed fine
  • 100 g unsalted butter, melted
  • 40 g caster sugar
  • 1 pinch fine sea salt

Filling

  • 400 ml grapefruit juice, freshly squeezed and strained (about 3 fruit)
  • 397 g sweetened condensed milk, one tin
  • 4 whole egg yolks
  • 2 tsp grapefruit zest, finely grated
  • 1 tbsp lime juice
  • 1 large grapefruit, segmented free of membrane and well drained

To serve

  • 300 ml double cream, softly whipped
  • 1 tbsp icing sugar

Method

  1. Heat the oven to 175°C. Mix the crushed biscuits, sugar, salt, and melted butter and press firmly into a 23 cm pie dish, up the sides as well as across the base. Bake for 10 minutes and leave to cool.
  2. Boil the grapefruit juice hard in a wide pan until it has reduced to about 150 ml. Cool it completely.
  3. Whisk the yolks with the zest for two minutes until noticeably paler and thickened, then whisk in the condensed milk, followed by the cooled reduced juice and the lime juice.
  4. Pat the grapefruit segments thoroughly dry, break them into pieces, and fold them gently through the filling. Pour into the cooled crust.
  5. Bake for 20 to 25 minutes, until the filling is set at the edges but still wobbles as a single mass in the centre when the dish is nudged.
  6. Cool to room temperature, then refrigerate for at least four hours or overnight. Serve with cream whipped with the icing sugar.

Notes

White grapefruit gives a better pie than pink, having more bitterness to set against the condensed milk, but ruby fruit gives a prettier colour. The reduction step is not optional. Some Gulf coast versions top the pie with meringue made from the leftover whites in the manner of a lemon meringue, and others go the other way and use no dairy on top at all. A pastry crust may be substituted for the biscuit crumb, blind baked. The pie keeps three days refrigerated and does not freeze well, the filling turning grainy on thawing.

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