Preparation. Brush and wash the grapefruits under running water. Peel them completely, removing the outer peel and the albedo which are very bitter.

Weigh the obtained pulp and add an equal weight of sugar.

Wash and thinly peel the orange as well (you can also simply cut it into chunks and let it macerate with the other ingredients), being careful not to take the inner white part (the orange peel will serve as a thickener). Also, squeeze its juice.

Break the grapefruit pulp directly into the pot you will use to cook the jam; in this way, you won’t waste the juice that will come out during this operation.

Pour in the sugar and a pinch of salt, add the peel and juice of the orange, mix, and let it marinate for at least an hour. During this time, the grapefruits will release their juice in contact with the sugar, making cooking shorter.

After the time has passed, turn on the burner, add the vanillin (or a quarter teaspoon of vanilla paste), mix, and over high heat, bring the fruit and sugar mixture to a boil.

At the same time, put the jars and lids to sterilize in a pot with water. From the first boil, let the jars sterilize for 20 minutes. Then take them out without burning yourself, dry them with clean kitchen towels. Also sterilize any other utensils you will use to touch or transfer the jam. I personally prefer to use small jars, from a minimum of 100 to a maximum of 200 grams, to avoid keeping the jam open for too long.

From the first boil of the fruit mixture, slightly lower the flame, uncover the pot and stirring often, count about 40/45 minutes of cooking at most.

The weight of the ingredients will reduce by more than half; this means you will obtain about 700 to 900 grams of jam.

After 35 minutes, check the density of the jam by doing the plate test: pour a teaspoon of jam on a coffee saucer and let it cool for 30 seconds. Tilt the saucer, and if the jam runs down too quickly, prolong the cooking for a few more minutes.

Do not overcook the grapefruit jam, as you risk ending up with a hard product that cannot be spread.

Also remember that hot jam is always much more fluid than cold jam. At this point, remove the orange peel if you don’t like it.

Turn off immediately and fill the already sterilized jars immediately, up to one centimeter from the edge. Seal them tightly and quickly turn them upside down, to allow the formation of a vacuum that will ensure long preservation.

Let the jars cool completely before turning them back and storing them. Grapefruit jam is already ready to be used.

Once opened, the jam is stored in the fridge well closed.

An extra idea. If you wish to make a jam that also contains grapefruit peels, you can do it this way. Cut the grapefruit peel into strips. Put them in a saucepan and cover with water. Bring to a boil and let it boil for 5 minutes. Discard that water and repeat this operation two more times. This way you ensure that the peels lose the bitter note. Then add them to the fruit before cooking the jam.