Safranal
Quick answer
The principal aroma compound of dried saffron — hay-like, honeyed and faintly metallic — and one that barely exists in the fresh flower. It is made during drying, from picrocrocin.
What it does
Safranal is most of what saffron smells of, and it is created rather than harvested: fresh stigmas carry little of it, and it forms as drying breaks picrocrocin down. That is why the drying step is treated as part of the quality of saffron rather than as mere preservation, and why saffron dried by different methods — gentle heat in the Spanish tradition, slower drying in the Iranian — smells different from the same flowers. ISO 3632 measures it by absorbance at about 330 nm as the standard’s aroma index.
How it behaves when cooked
Four properties of the molecule, and what they mean at the stove.
- Volatility
- high
- Fat solubility
- moderate
- Water solubility
- low
- Heat stability
- low
Volatile and fragile, which dictates two things. In the kitchen, saffron’s aroma is the first thing a long boil destroys: the colour survives a paella or a risotto, and the smell survives only if the steeped threads went in late enough. In the cupboard, safranal is lost over months and faster in light and warmth, which is why old saffron still colours rice and no longer smells of anything — the colour compound is far more stable than the aroma compound, so colour is a poor guide to freshness. Keep saffron sealed, dark and cool, and judge it by smell.
Not present until the plant is damaged
Picrocrocin + β-glucosidase, with heat
Released during drying, when the glucose of picrocrocin is split off — partly by the stigma’s own enzymes and partly by heat — and the aroma molecule is freed. The drying method therefore sets how much safranal the finished spice starts with.
Spices that carry it
Recorded on the compound rather than on each spice, so the two cannot disagree.
The aroma of saffron. Formed on drying, from picrocrocin, lost during storage, and the property that distinguishes fresh saffron from old saffron that still colours well.
What cooking and processing were measured to do to it
Findings from studies in which this compound was followed through heat, fat, water, drying or storage. Each belongs to its study and its conditions.
Infusing in oil · Extracts Safranal
Safranal, the principal aroma compound of saffron, behaved in the opposite way to the colour. In pure water it was found only in traces. It was recovered best where oil was present, reaching 12.3 µg per mg of saffron at 80 °C in a mixture of one part water to two of oil. At 100 °C with water present its level fell significantly, while in pure oil it went on rising with temperature and time.
Conditions: in oil or fat · 60, 80 and 100 °C · 10 to 30 min · Ground saffron in water, olive oil or mixtures of the two
The colour and the aroma of saffron want different media: water takes the one, fat holds the other. A dish that contains both, as most saffron dishes do, has somewhere for each to go.
What this does not show: The fall at 100 °C in the presence of water was measured in the liquid, so it does not distinguish safranal driven off as vapour from safranal broken down. Safranal is also formed from picrocrocin on heating, which the design cannot separate from extraction.
Measured on the spice
Simmering and boiling · Retains Picrocrocin, Safranal
Picrocrocin proved highly stable in water. Its half-life ranged from more than 3400 h in saffron extract at 5 °C to 9 h for the purified compound in water at 100 °C. In the purified compound at 100 °C, safranal was confirmed to form during the first 5 h, with a yield of up to 7.4 per cent.
Conditions: in water · 5 to 70 °C for saffron extracts; 100 °C for purified picrocrocin · Aqueous extracts and purified compound; second-order kinetics
Over the length of time a dish is cooked, very little of saffron’s bitter compound breaks down, and only a small part of what does becomes aroma. Cooking is not a significant way of making safranal.
What this does not show: Read in the abstract only. Extracts and pure compound in the laboratory, in the dark; the abstract notes that the rate in whole extracts behaved irregularly with temperature, peaking at 35 °C.
Measured on the pure compound
Drying · Increases Safranal
Summarising work that compared three types of drying, the review reports that the safranal detected in saffron increased with drying temperature, in the order oven, then sun, then shade. It sets this beside the account of safranal formation: the compound is absent from the fresh stigma and arises from picrocrocin by enzymatic action or by dehydration under heat, and saffron dried at high temperature has no active enzymes left, so that in such saffron the volatiles come from thermal breakdown.
Conditions: in air · Oven drying at high temperature, sun-drying at ambient temperature, and shade-drying, as compared in the literature reviewed
What this does not show: A review’s summary of other studies, without the figures behind the ranking. More safranal is not the same as better saffron: the same heat acts on the crocins that give the colour.
Review of studies
Drying · Depends on conditions Safranal, Crocin, Picrocrocin, HTCC (4-hydroxy-2,6,6-trimethyl-1-cyclohexene-1-carboxaldehyde)
When the drying time at a given setting was lengthened, crocin and picrocrocin in saffron barely moved while safranal swung widely. In an electric oven at 50 °C, extending drying from 50 to 65 min raised crocin by 1.81 per cent and safranal by 26.90 per cent. At 60 °C, going from 45 to 60 min raised crocin by 1.13 per cent but cut safranal by 23.13 per cent; at 70 °C, 30 to 45 min raised safranal by 13.18 per cent. In a microwave at 600 W, doubling the time from 3 to 6 min cut safranal by 58.59 per cent and crocin by 1.10 per cent while the picrocrocin peak rose by 13.84 per cent. The authors explain the pattern as formation and degradation proceeding at once, at rates that depend on temperature.
Conditions: 50, 60 and 70 °C in ovens; 450 and 600 W in a microwave · Each setting compared at a shorter and a longer time
What this does not show: Percentage changes in chromatographic peak area between two settings, not absolute contents. One harvest day, small lots, no replication across seasons. The changes in safranal do not run in one direction, so the study supports sensitivity, not a rule.
Measured on the spice
Storage · Depends on conditions Safranal, 4-hydroxy-2,6,6-trimethyl-1-cyclohexene-1-carboxaldehyde (HTCC), 3,5,5-trimethyl-2-cyclohexen-1-one
Across 73 saffron samples in three age groups, safranal remained the main volatile at 30.14 to 43.94 per cent of the total, but the profile changed with age. The major compounds differed significantly between saffron less than a year old and saffron stored for three to four or eight to nine years. Saffron under a year old carried more of the notes described as saffron, flower and spicy; the older saffrons carried volatiles with vegetal, caramel and citrus notes.
Conditions: Under 1 year, 3 to 4 years, and 8 to 9 years · 73 samples in three age groups
What this does not show: Read in the abstract only. The samples in the three groups are different saffrons, and the abstract does not describe how they had been stored.
Measured on the spice
Storage · Depends on conditions Crocin, Picrocrocin, Safranal, β-isophorone, 4-hydroxy-3,5,5-trimethylcyclohex-2-enone, colour
Comparing freshly dried saffron with saffron stored for two years, the authors found that the fresh samples held more of the crocins, of picrocrocin and of two minor volatiles, while the stored samples held more safranal. They conclude that during storage the intensity of saffron’s colour falls while its aroma compound increases, the two moving in opposite directions.
Conditions: Freshly dried against two years of storage
Old saffron can smell strongly of safranal and still have lost much of its colouring power, so smell alone is a poor guide to its condition.
What this does not show: Read in the abstract only, which gives relative levels and no figures, and does not state the storage conditions.
Measured on the spice
Not to be confused with
Compounds a reader is likely to take for this one, and why they differ.
Picrocrocin
Its precursor. The two are measured separately in saffron grading, and their ratio carries information about drying and age.
Questions this page answers
- what is safranal
- what gives saffron its smell
- saffron aroma compound