2,5-Dimethylpyrazine
Quick answer
One of the pyrazines behind roasted and nutty notes, named rather than left inside the word “pyrazines”: it forms when nigella, sesame or poppy seed is roasted, and it turns up in some shrimp pastes, where fermentation, sun-drying or both may be what makes it.
What it does
Pyrazines such as 2,5-dimethylpyrazine and trimethylpyrazine are typically associated with roasted or nutty notes. In roasted nigella seed, methylpyrazine and 2,5-dimethylpyrazine were the major pyrazines, and the rise of pyrazines and furans with roasting was proposed as part of the flavour of the roasted seed. In oil pressed from roasted sesame seed it was identified by smell at the chromatograph as roasted and nutty, among pyrazines that were the most abundant group of odorants in the oil.
How it behaves when cooked
Four properties of the molecule, and what they mean at the stove.
- Volatility
- high
- Fat solubility
- moderate
- Water solubility
- moderate
- Heat stability
- high
It is made by heat rather than lost to it. In nigella seed, 2,5-dimethylpyrazine was formed at high concentration after eight minutes of microwave roasting and after conventional roasting, while the raw seed’s thymoquinone and p-cymene fell — which is why dry-roasting a seed changes its character rather than only intensifying it. Sesame shows the same thing from the other side: the compound was absent from oil pressed from raw seed and present in oil from seed roasted in hot air or by microwave, and the pyrazines as a group rose with roasting time and then fell when roasting went too far. Heat is not the only route: in Indonesian shrimp pastes it was found in some samples, and the authors note that bacteria such as Bacillus subtilis can make pyrazines during fermentation, alongside the effects of sun-drying.
Spices that carry it
Recorded on the compound rather than on each spice, so the two cannot disagree.
- DouchiContributing component
Measured in finished Yongchuan douchi, where it smells nutty, and one of two pyrazines from it that made a weak salt solution taste saltier to a panel. Nothing read measured it in the beans before or while they fermented, so how it comes to be there is not shown: the authors describe pyrazines in general as products of browning reactions and of microbial metabolism, without saying which accounts for it here.
Formed on roasting; it is a compound of toasted nigella seed, not of the raw seed.
The pyrazine found in the largest amount in oil pressed from seed roasted at 150 °C, in two of three varieties, and absent from oil of unroasted seed. Measured in the oil, not in the seed.
Found in oil pressed from roasted seed and absent from oil of raw seed; one of many pyrazines there, and measured in the oil, not in the seed itself.
- Shrimp pasteContributing component
Found in some commercial terasi and not others, from fermentation, sun-drying or both.
- Thua naoContributing component
The most abundant pyrazine in dried discs of thua nao made in one laboratory from black soybeans with a starter culture: most in sun-dried discs and least in vacuum-dried ones. That study measured the finished discs only, so it does not show whether the fermentation or the drying put it there; its authors point to browning during drying.
Not to be confused with
Compounds a reader is likely to take for this one, and why they differ.
Guaiacol
Both bring a cooked, dark note to a spice, by different routes: pyrazines form from the food’s own sugars and amino acids when it is heated, guaiacol mostly arrives from wood smoke, though hard roasting can form a little of it too.
Questions this page answers
- why do roasted seeds smell nutty
- what is 2,5-dimethylpyrazine