日本語版

Research note 016 — 2026-08-31 (expanded 2026-09-08)

Is That Spice Really Bitter?

It is easy to write that a spice is 「苦い」 (in translation: "bitter"). But in the mouth, aroma, warmth, pungency, tingling, irritation, and aftertaste all happen at once. This note discards no candidates, and separates what has actually been measured from what is still only a hypothesis about naming.

What this page establishes

• In mustard seed, it has been confirmed that sinigrin is placed as bitterness and allyl isothiocyanate (AITC) as pungency, positioned separately in threshold testing.
• In Brussels sprouts, once the combined content of sinigrin and progoitrin exceeds 2.2 g/kg, a correlation with preference has been confirmed across multiple trials.
• It has been confirmed that the principal compounds of clove and oregano produce numbness/tingling and warmth on the human tongue, but whether this can be called a 「苦い後味」 (in translation: "bitter aftertaste") has not yet been confirmed.
• Whether cumin's bitterness can be called a primary attribute of its flavor has not yet been settled.

Turmeric Has Sensory Evidence in Food

In ice cream containing turmeric, as the added amount increased, bitterness, aftertaste, aroma, and overall taste intensity all increased. This is, however, a single food that contains milk fat and sugar. We do not treat this as a fixed 「苦味点」 (in translation: "bitter point") for turmeric.

This direction of increase is not limited to a single food containing milk fat. In a functional-beverage blend combining pineapple juice with turmeric juice as well, the bitterness-intensity evaluation by a trained sensory panel showed its highest value in the sample with a 20% turmeric proportion. Even when the matrix changes, the direction in which the bitterness score rises as the blend grows more concentrated is shared.

In Mustard Seed, the Carriers of Bitterness and Pungency Diverge

In human threshold testing, sinigrin was answered mainly as bitterness, and allyl isothiocyanate mainly as pungency. Even for sensations that can arise one after another within the same mustard seed, the receiving system is not the same.

Sinigrin's bitterness is not a story limited to mustard seed. Across 4 taste tests on Brussels sprout cultivars, in cultivars where the combined content of sinigrin and progoitrin exceeded 2.2 g/kg, a relationship was confirmed in which preference fell as content rose. In cultivars below this threshold, however, no relationship between content and preference was observed, while the correlation with bitterness did not break off across the content range. Even for the same glucosinolates, the force that moves preference and the force that generates bitterness do not necessarily act with the same strength. Within the scope of the abstract, this is how the two diverge.

The Lingering Sensation of Clove and Oregano May Be Warmth and Tingling

In studies that applied clove's eugenol and oregano's carvacrol to the human tongue, multiple stimuli centered on warmth and tingling were reported. The stimulation weakens with repetition. It is possible that the eater names the lingering sensation 「苦い後味」 (in translation: "bitter aftertaste"), but that remains a hypothesis.

For marjoram (Origanum majorana), a species in the genus Origanum, an official assessment report goes a step further in how it is written. This plant is described as an aromatic plant with a distinctive pungent aroma together with bitterness, with a volatile-oil content of up to 5% (usually less than 1%) and its principal constituents described as terpinen-4-ol and (+)-cis-sabinene hydrate. The 「苦味」 (in translation: "bitterness") used here is a different word from the warmth and tingling reported by sensory tests that apply carvacrol to the tongue; it is written as a property of the plant itself. This description, however, is a property description of marjoram alone within the genus Origanum, and cannot be extended to other species in the genus.

Thyme and Cumin Are Held Back in Different Ways

Thyme's thymol activates the warmth-type channel TRPV3, but this is not a sensory test of eating thyme as cooked food. For cumin, the flavor and lingering aftertaste of commercial samples have been analyzed, but the abstract could not confirm 「苦味が共通の主要属性」 (in translation: "bitterness as a shared primary attribute"). Both have been promoted to the encyclopedia, while the broader claim of a 「苦いスパイス」 (in translation: "bitter spice") remains unverified.

Frequently asked

Is turmeric a bitter seasoning?

Studies using ice cream containing turmeric report that the scores for bitterness, aftertaste, aroma, and overall taste intensity rise as the amount added increases. In a beverage blending pineapple juice and turmeric juice as well, the sample with the proportion raised to 20% showed the highest bitterness score. Both share the direction that the bitterness score rises as more turmeric is added, but these are results from specific foods containing milk fat or sugar, and this is not a source that measured the bitterness of the powder itself as a single number.

Why does mustard seed feel both sharp and bitter?

In threshold testing on sinigrin and allyl isothiocyanate (AITC), both contained in mustard seed, sinigrin is reported to have been answered mainly as bitterness and AITC mainly as pungency. This is thought to be because the same seed contains separate compounds that each carry a different sensation. This testing measured detection thresholds in aqueous and oil systems, and no significant difference was found between people who use mustard daily and those who do not.

What is not known

• Whether the warmth and tingling that the principal compounds of clove, oregano, and thyme give to the human tongue are felt, in actual cooking, as a 「苦い後味」 (in translation: "bitter aftertaste") has not yet been confirmed.
• In cumin's flavor profile, whether bitterness can be called a shared primary attribute has not yet been settled by analysis of commercial samples alone.
• When the combined content of sinigrin and progoitrin in Brussels sprout cultivars falls below 2.2 g/kg, what happens to the relationship with preference has not been observed; only the correlation with bitterness has been confirmed.

Related: The Boundary Between Bitter, Astringent, and Pungent / Spice and herb encyclopedia / Hypothesis Box