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Topic hub — 2026-09-16

Chicory and radicchio bitterness

The bitterness of chicory and radicchio cannot be measured on a single scale. Although they are all varieties of the same species, chicory (Cichorium intybus), Treviso, Castelfranco, Chioggia, Verona, and puntarelle each hold their own separate EU specification. The specifications use a degree word for bitterness (leggermente, "slightly") and a separate evaluation word (gradevolmente, "pleasantly"), and the two cannot be compared on the same scale. Treviso's early type is described with the degree word "slightly", yet the measured total of sesquiterpene lactones was reported as the highest of the four varieties studied. Blanching itself is not one uniform process either: in witloof chicory, forcing sharply increases bitter compounds not in the edible new shoot but in the root stump left behind, while Radicchio Rosso di Treviso's early type goes through a different kind of blanching altogether — tying (legatura) in the field rather than immersion in water. In the kitchen, washing fresh-cut chicory in warm water has been measured to substantially lower compound levels, while the effect of salt-rubbing or the way it is cooked has not been measured here. Anyone who has ever picked over the outer leaves of frisée for a salad, or drunk chicory in place of coffee, has in fact touched the same lineage of bitterness carried by the genus Cichorium. Here, each of these is kept separate and laid side by side.

What this page shows

• Treviso's early type (precoce) is described in its specification, using a degree word for bitterness, as "slightly bitter"; but a study comparing four varieties by Orbitrap-HRMS/MS-MS reported its total sesquiterpene lactones at 189.71 µg/g, the highest of those studied. The late type's (tardivo) specification is written with an evaluation word for pleasantness rather than a word for bitterness strength, so it is not even something whose degree can be compared in the first place.
• When witloof chicory is forced, lactucin and related compounds increase sharply in the inedible root stump, while the amount in the edible new shoot has been reported to stay about the same whether the root was stored for 1 month or 12.
• The production specification's original text states that Radicchio Rosso di Treviso's early type is not blanched by immersion in water, but goes through a separate process called legatura, in which the leaves are tied in the field to stop photosynthesis.
• One study measured that washing fresh-cut witloof chicory in warm water lowers total sesquiterpene lactones by 60.9–64.5%, while the effect of salt-rubbing or the way it is cooked on bitterness itself has not been measured within the scope of this page.

What bitterness comes from

A study comparing fresh chicory root with its roasted coffee-substitute powder quantified lactucin and lactucopicrin, two sesquiterpene lactones, as the principal compounds. The raw root contained roughly 42.13±4.10 µmol/g of lactucin, which remained at roughly 32.48±5.87 µmol/g even in the roasted coffee-substitute powder, but the concentration fell to 1.35±0.10 µM once it was made into a prepared extract. The study reports that it was not present in roasted coffee itself.

Lactucopicrin followed the same pattern in the same root: roughly 11.93±0.46 µmol/g, roughly 10.66±0.94 µmol/g in the roasted powder, and down to 0.45±0.04 µM in the extract.

Lactucin has been confirmed as a compound that contributes to chicory's bitterness. Lactucopicrin is a closely related sesquiterpene lactone obtained from the same root.

Even within the single name "sesquiterpene lactone", the compounds differ widely in sensory threshold. A review compiling earlier sensory-threshold studies records that dihydrolactucopicrin was detected at a concentration as low as 0.2 ppm.

What differs by variety and origin

Treviso's red radicchio is classified, under the EU geographical indication specification, as belonging to the silvestre variety of chicory, and defined as consisting of two types: the early type (precoce) and the late type (tardivo).

The word the specification chooses for each type does a different job. The leaves of the precoce type are described as having a "slightly bitterish taste" (leggermente amarognolo), andleggermente is a word that indicates the degree of bitterness.

The tardivo type, by contrast, describes the taste of the midrib as "pleasantly bitterish" (gradevolmente amarognolo). As the research note "Italy's Bitter Vegetables" lays out,gradevolmente is a word that adds an evaluation of pleasantness, not a word that states the strength of bitterness itself. Even though both modify the same amarognolo, leggermenteand gradevolmente do different jobs, and cannot be placed on one scale.

A study that quantified sesquiterpene lactones across four varieties by Orbitrap-HRMS/MS-MS reports that the precoce type's total was 189.71 µg/g, the highest among those studied, of which lactucopicrin alone accounted for 99.36 µg/g. The side described with the degree word "slight" has the largest measured compound total of those studied.

In the same study, the tardivo type's total was 45.78 µg/g, with lactucopicrin at 13.50 µg/g — the lowest of the four varieties. Because tardivo's specification is written using only the evaluation word and states nothing about the strength of bitterness, this number cannot be judged as matching or not matching the specification's wording. The study itself also notes that genetic differences between varieties and differences in process are confounded, so the difference in compound totals cannot be attributed to variety alone either.

Chioggia's radicchio is likewise defined as the same variety, comprising two types, early and late.

An HPTLC analysis of 3 Chioggia-type lines reports that the content of guaianolides linked to bitterness varied widely — between growth stages, between plant parts (head, outer leaves, and root), and between the 3 lines. The cultivar name "Chioggia" alone cannot settle bitterness to a single amount.

The name "puntarelle", for the young flower stalks of chicory eaten as a vegetable, does not belong to a single place of origin either. Cicoria puntarelle molfettese, from around Molfetta in Puglia, covering the head and young flower stalks, has been under application for EU geographical indication registration since 2026.

The application itself describes the aftertaste of the young flower stalks as sweet with a light bitterness, and also states that this bitterness increases as the plant grows.

A different puntarelle, however — Cicoria di catalogna frastagliata di Gaeta, grown in Formia, Gaeta, and Santa Marinella in Lazio — is recorded in the regional park agency's product introduction as an elongated plant about 40–50 cm long, with harvest beginning 40–45 days after sowing.

Separately from Puglia's EU registration application, this one is registered as item 156 on Lazio's list of traditional agri-food products (PAT). Young flower stalks that look very similar belong to separate systems on either side of the regional border.

There are relatives outside the name "chicory" too, distinguished by the strength of their bitterness. Frisée belongs to the same genus Cichorium as chicory, but its species is not Cichorium intybus — it is Cichorium endivia var. crispum, a different species from chicory.

An RNA-seq analysis comparing frisée with its close relative scarole (var. latifolium) positions frisée as the more bitter variety and scarole as the less bitter one, and reports that expression of the gene group involved in sesquiterpene lactone biosynthesis was higher in the more bitter cultivar. However, this finding covers C. endivia as a whole, and a doctoral thesis that organized the original paper adds the reservation that the abstract does not go so far as to specify the cultivar names frisée and scarole.

Outside Italy, there is a spiny chicory called stamnagathi on the Greek islands of Crete and Ikaria. It belongs to the genus Cichorium but is a different species, Cichorium spinosum; it has a bitter flavor and is recorded as being harvested at a young growth stage and either boiled or eaten raw in a salad.

What changes with blanching and tying

Blanching is the most deliberately engineered transformation within the species chicory. In witloof chicory, cold-stored roots are forced for about 3 weeks in a multilevel hydroponic system at 15–16°C in darkness, to form white new shoots (chicons).

What increases sharply from this forcing is not the edible new shoot but the root stump left behind afterward. In the root-stump tissue after forcing, lactucin has been reported to increase from 51.3±5.5 to 128.3±9.6 µg/g DW (cv. Sweet Lady, after 12 months of cold storage).

The same study also records that in the same root-stump tissue, lactucopicrin likewise increased from 31.5±9.5 to 75.8±1.5 µg/g DW.

The sesquiterpene lactone content of the edible head, by contrast, stayed about the same whether the root was stored for 1 month or 12, with no significant difference, the same study reports. The part where forcing increases bitter compounds is the part that never reaches the table.

Blanching is not only a matter of soaking in water. The production specification's original text states that Radicchio Rosso di Treviso's early type (precoce) is blanched through a process called legatura, in which the plant is left standing in the field and its leaves are tied to stop photosynthesis.

This is a separate process from what the same Treviso's late type (tardivo) undergoes. The tardivo type's production specification includes a process called forzatura (forcing), in which the plant is immersed vertically in a water source to blanch it.

Although it belongs to the same variety, Chioggia's production specification does not describe this process at all. Reading the entire original text, the words forzatura (forcing) andimbianchimento (blanching) never appear even once; what it specifies is only the harvest method of cutting the root and hand-shaping with a sickle-shaped knife. The choice not to describe a blanching process can itself be read as part of the specification.

The same idea of blanching is used outside chicory too. In frisée, light is blocked by tying the outer leaves with string, or by removing the outer, darker-colored leaves after harvest and using only the center. Cultivation guidance explains that the outer leaves are strongly bitter while the inner, pale leaves shielded from light are less bitter, and positions blanching as working to delay chlorophyll production.

What is known and not measured in the kitchen

Amounts also shift in the steps after harvest and packaging. A study comparing fresh-cut witloof chicory across multiple washing conditions — cold water, warm water, and cysteine-added water — reports that sesquiterpene lactone content and bitterness dropped significantly under every washing method, with warm-water washing lowering the total by 60.9–64.5%.

As storage progresses, the lineup of compounds changes too. The same washing-and-storage trial also records that dihydrolactucin became the predominant sesquiterpene lactone by the end of storage.

For people who drink chicory as a coffee substitute, there is one more thing that has been measured. A controlled sensory order-effect test with 16 participants reports that drinking chicory after roasted coffee lowered its bitterness rating, while reversing the order left the bitterness of the roasted coffee drunk after chicory unchanged. The authors explain this as roasted coffee activating a broader set of receptors and desensitizing, ahead of time, the receptors that chicory's lactones act on — but this is the authors' interpretation, not an independently verified mechanism.

There are also records of dishes that pair with chicory. Fave e cicoria, a traditional Puglian dish, is recorded as skinned dried fava beans soaked in water then simmered into a purée, served with boiled wild chicory or catalogna-type chicory.

Wild chicory, too, has traditionally been hand-picked in Puglia. It is recorded that farmers cut it with a knife, selected plants they knew to be edible, knocked off the soil and washed it repeatedly, then ate it raw as "spincituru". How much salt-rubbing or the way it is cooked itself moves the bitterness of chicory or radicchio has not been measured within the scope of this page. What has been measured are the steps of washing and storage that come before cooking begins.

Frequently asked

Which is more bitter, Treviso's early or late type?

The wording of the specifications alone cannot settle this. The production specification describes the leaves of the precoce (early) type, using a degree word for bitterness, as "slightly bitterish". The midrib of the tardivo (late) type, by contrast, is described using an evaluation word for pleasantness, as "pleasantly bitterish", and says nothing about the strength of bitterness itself. A study that quantified sesquiterpene lactones across four varieties reports the precoce type's total at 189.71 µg/g — the highest of those studied — and the tardivo type's at 45.78 µg/g, the lowest. A mismatch between wording and number can be pointed out: the side described with the degree word "slight" has the largest measured compound total. But because the tardivo side is written using only the evaluation word, this number cannot be judged as higher or lower against the specification's wording. Genetic differences between varieties and differences in process are also confounded, so the difference in compound totals cannot be attributed to variety alone either. So neither the wording of the specifications nor this compound quantification alone can directly settle which is more bitter.

Are chicory, radicchio, and frisée the same vegetable?

They belong to the same genus Cichorium, but their species and processes diverge. Radicchio, puntarelle, and witloof chicory are all, as species, Cichorium intybus — only their variety and way of cultivation differ. Frisée, by contrast, is a different species,Cichorium endivia var. crispum, and differences have been reported even at the level of gene expression when compared with its close relative scarole (another variety of the same species). Greece's stamnagathi goes further still, being yet another species, Cichorium spinosum. Even when lumped together as "chicory's relatives", several genuinely different species are actually included.

How does blanching change radicchio's bitterness?

What increases is often not the part that gets eaten. In witloof chicory's forcing, sesquiterpene lactones such as lactucin increase sharply in the root-stump tissue left behind after forcing, while the amount in the edible new shoot (chicon) has been reported to hardly change whether the root was stored for 1 month or 12. In Radicchio Rosso di Treviso, the precoce type goes throughlegatura, tying the leaves without soaking them in water, while the tardivo type goes through a separate process, forzatura, immersing the plant in a water source. Chioggia, of the same variety, goes further still: the words forzatura and imbianchimento never appear even once in the original text of its production specification. Blanching is not a process that uniformly increases or decreases bitterness — it works through a different mechanism for each variety.

What is not known

• Whether the production specifications' wording — "slight" and "pleasant" — reflects an actually measured difference in bitterness intensity has not been confirmed within the scope of this page. Leggermente (a degree word) and gradevolmente (an evaluation word) do different jobs, and whether the two can even be compared on the same scale at all has not yet been confirmed.
• How much salt-rubbing or the way it is cooked itself moves the bitterness of chicory or radicchio has not yet been measured.
• No source directly comparing Chioggia-type guaianolide content between the early and late types has yet been found. The HPTLC study covers the Rosso di Chioggia variety as a whole and does not distinguish between early and late.
• How far the difference in gene expression between frisée and scarole corresponds to an actual sensory strength of bitterness has not been confirmed. The RNA-seq analysis does not involve direct compound measurement or sensory evaluation.

Read in the encyclopedia

• chicory — the species itself, to which most of the varieties belong
• Radicchio Rosso di Treviso (precoce / tardivo) — the origin where the specification's wording (degree vs. evaluation) does not simply match the measured compound totals
• Radicchio Variegato di Castelfranco / Radicchio di Chioggia (early / late) / Radicchio di Verona (tardivo) — other radicchio with their own separate EU specifications
• Cicoria puntarelle molfettese (Catalogna pugliese and others) — young flower stalks from Puglia, under EU registration application
• Cicoria di catalogna frastagliata di Gaeta (Puntarelle) — a different puntarelle registered on Lazio's PAT
• witloof chicory / witloof chicory forcing — the product and process where forcing the root moves bitter compounds
• radicchio forcing and blanching — the blanching process by immersion in water
• frisée — a different species in the Asteraceae genus Cichorium from chicory
• stamnagathi (stamnagathi salad) — Greece's spiny chicory
• Cicoria selvatica (wild chicory greens) / Fave e cicoria — Puglia's wild chicory and the traditional dish that uses it
• lactucin / lactucopicrin — the principal sesquiterpene lactones behind chicory's bitterness

Go deeper in the research notes

• Italy's Bitter Vegetables — Chicory, Radicchio, Artichoke — compares, in a table with the original-language wording, how each origin's specification differs between "slight" (a degree word) and "pleasant" (an evaluation word) in more detail
• Can Bitterness Be Cultivated? — The Four Reins — places witloof chicory's forcing and Treviso's blanching within the broader agronomic framework of breeding, environment, process, and harvest timing
• Can Cooking Create Bitterness? — positions Castelfranco's blanching alongside roasting, debittering, and suppression as a process that "designs" bitterness
• 「苦い」 Is Not a Single Taste — digs into how chicory's two bitter compounds, lactucin and lactucopicrin, strike separate receptors even within the same plant

Source ledger

The primary sources and limitations behind the claims on this page can each be checked from the source links inside their card. The full list is gathered in theSource ledger.