For the quince-grapefruit chutney, first rub the quinces with a kitchen towel so that the fluff comes off the peel. Then peel the fruit, cut into eighths, remove the core and cut the flesh into flakes.
Peel the shallots and cut them into eighths.
Peel and finely chop the garlic.
Peel ginger thinly and dice finely.
Place quinces in a pot with the shallots and garlic.
Fillet the grapefruits: Peel off the peel including the white inner skin, reserving the juice. Then separate the grapefruit segments from the thin intermediate membranes, also collecting the juice.
Cut the grapefruit fillets slightly smaller and add them to the saucepan with the collected juice.
Add the ginger and the remaining ingredients to the pot as well and bring everything to a boil. Turn down the temperature and let everything simmer for about 2 hours, stirring frequently.
In between tasting, once the quinces are soft, pour the chutney hot into clean twist-off jars. Turn these upside down a little at first, then invert and let chill.
Unopened, the quince-grapefruit chutney will keep for about 6 months. Store opened jars in the refrigerator and use soon.