Radicchio
Radicchio in more detail
Radicchio is a red-leaved chicory from the Veneto, and its defining characteristic is bitterness — not as a flaw to be worked around but as the entire point. It belongs to the same species as Belgian endive and the same family as dandelion, and the bitter compounds are sesquiterpene lactones concentrated in the white ribs.
The named Italian types are genuinely different vegetables in the kitchen. Radicchio di Chioggia is the round, tight, dark red head sold in most UK supermarkets and the sharpest of the common types. Treviso is elongated, looser and noticeably milder, and it is the one to grill. Castelfranco is a pale, speckled, open rosette, mildest of all, and is used raw as a salad leaf.
Two techniques tame the bitterness rather than hiding it. Heat converts some of the bitter compounds and brings out sugars, which is why grilled or roasted radicchio is sweet and faintly smoky where the raw leaf is astringent. And bitterness is chemically balanced by fat, salt and acid together — the classic Venetian treatment of radicchio with pancetta, balsamic and a hard cheese is not decoration, it is the counterweight.
Soaking cut leaves in cold water for half an hour genuinely reduces bitterness, at some cost to texture.
Nutrients worth knowing about
At 23 kcal per 100 g, radicchio is a low-energy leaf. It supplies Vitamin K — the standout nutrient in chicories generally — along with Vitamin B9 (Folate / Folic acid), Copper, Potassium and Vitamin C.
The red pigment is anthocyanin, the same class of compound as in Blackcurrant and red cabbage. It is not a nutrient with a reference intake. Anyone taking warfarin is usually advised to keep vitamin K intake steady rather than variable, which makes leafy greens a thing to be consistent about rather than to avoid.