Where does
aroma come from?
Apple · Lychee · Aged caramel · Fishiness — all of it

Yeast makes caproic acid as an intermediate of fatty acid synthesis, and that is then esterified with ethanol.

One of the esters that make up ginjo aroma. Yeasts bred to produce more of it are reported.

★ For that reason the textbook line that ginjo aroma will not appear unless the rice is heavily polished may now be too simple. With high-ester yeasts (Kyokai No. 1801 and others) in wide use, it can form without heavy polishing. ⚠️ But that second half, tying yeast strain to polishing ratio, is inference; no supporting report has been found.

Formed when yeast esterifies isoamyl alcohol (one of the fusel alcohols) with acetic acid.

Its precursor is a fusel alcohol, so these two families stand in an upstream-downstream relation. In juicy-style sake the fruit character can sit on this softer side rather than on ethyl caproate.

★ Formation is reported to be suppressed where unsaturated fatty acids are abundant. Part of the reason for the length of steaming, and for polishing the rice further in ginjo, lies here. Cutting the fat is what leads to more aroma.

⚠️ Not established in the sources. It is known to be higher in wines made without sulfites, but why it is higher is not shown.

The shape of the molecule is an ester, but yeast does not make it. It does not fit this family's account of yeast assembling the molecule.

★ Identified as an odour-active compound in Bordeaux reds made without sulfite, by aroma fractionation and GC-O. Content is significantly higher in the sulfite-free wines, and it is reported to work on both the fruit character and the freshness.

The interesting part is that smelled on its own it is medicinal, like a compress, yet inside the wine it works on the side of coolness. The impression of a compound and the impression that compound brings to a wine are separate things.

⚠️ Why it is higher without sulfite is not answered by the source. Whether sulfite stops something, or a different route runs, is not known.

⚠️ Wine research; it does not cover sake.

Made by yeast joining acetic acid and ethanol. The simplest combination among the esters, and often the most abundant ester in both sake and coffee fermentation.

★★ That yeast increases it has been pinned down experimentally. In a study inoculating Pichia fermentans into on-farm washed processing, ethyl acetate and isoamyl acetate rose together with ethanol and acetaldehyde. The study also followed through to the roasted beans, where yeast-derived volatiles stayed higher in the inoculated treatment. Cupping brought out vanilla and floral impressions.

★ Coffee fermentation turns up the same cast as sake. In a study of spontaneous fermentation in Mozambique, read from both the microbial and the metabolite side, the three most abundant volatiles produced were linalool, phenethyl alcohol and ethyl acetate; the gene repertoire of the organisms involved points to the Ehrlich pathway and ester biosynthesis as the central routes to aroma. The same route that makes isoamyl alcohol and phenethyl alcohol in sake is turning in coffee as well.

★ In yeast-inoculated coffee fermentation, esters fall on roasting, yet the inoculated treatment is reported to stay significantly higher than the control. An instance of a difference set at fermentation surviving a high-temperature step.

⚠️ Both are coffee research, not sake research. The threshold and content in sake have not yet been confirmed.

Present in the raw material as odourless cysteine and glutathione conjugates, and set free during fermentation when a yeast beta-lyase cleaves them.

Established in wine and beer, but public quantitative data for sake is thin. In beer, disulfide-bound precursors have been found in malt and hops; during fermentation 65-82% are reduced and the 3MH concentration rises 9.5- to 14.2-fold.

Present in the raw material as a precursor, and set free during fermentation by yeast enzymes.

The best-studied thiol in sake. In spiking trials, a sulfury note lifts once the concentration passes 8.0 ng/L.

★ The interesting part comes after that. Above 16.0 ng/L the muscat, lychee and citrus notes do grow stronger — but the overall flavour rating of the sake went down. More of the showy aroma did not make a better drink. Worth keeping as the counter-example to "more aroma is better".

Formed when 3MH released during fermentation is esterified with acetic acid by yeast.

A derivative of 3MH, so it presupposes that 3MH is there. Its threshold is extremely low, and a trace is enough to set the direction of the aroma.

Stored in the plant as a glycoside, and set free during fermentation when a yeast beta-glucosidase removes the sugar.

In wine it is treated as the main factor in muscat aroma. Public quantitative data for sake is thin.

★ In coffee fermentation too it comes top among the abundant volatiles. In the study of spontaneous fermentation in Mozambique, linalool was most abundant alongside phenethyl alcohol and ethyl acetate, emerging as a predictor of floral scores. ⚠️ That study, however, does not separate where the linalool came from — whether glycosides in the raw material came undone, or microbes made it. The grounds on which this map places linalool on the released-from-glycoside side are other sources, not this study.

⚠️ Coffee research, not a statement about sake.

Stored in the plant as a glycoside, and set free during fermentation when the sugar comes off.

In beer, yeast is reported to convert geraniol into citronellol during fermentation. An instance of hop-derived aroma not simply coming through as it is, but being remade by the fermentation.

Released from glycosides, and also reported to arise when yeast converts geraniol during fermentation.

From the grapes. The route usually described is cyclisation from citronellol.

Often described as the compound that decides the lychee note of Gewurztraminer. But the lychee impression also shifts with the overlap of other terpenes, so it may not be settled by this one molecule alone.

⚠️ Of everything set out here, this compound has the thinnest support. Neither the threshold nor the formation route has been traced back to the original research.

Formed as yeast metabolises the amino acid phenylalanine. More is made at a higher rice polishing ratio and a higher fermentation temperature.

Within the showiness of ginjo, it carries the floral side rather than the fruit side. The source treats it as part of the base aroma of sake.

★ The interesting part is that the range of content (75-200 mg/L) straddles the threshold (130 mg/L). The same compound sits right on the border of being perceptible or not, depending on the sake. There are also yeasts bred to make more of it.

★★ In coffee fermentation this compound also comes up as a lead player. In the study of spontaneous fermentation in Mozambique, read from both the microbial and the metabolite side, the three most abundant volatiles produced were linalool, phenethyl alcohol and ethyl acetate, emerging as predictors of floral and fruity scores. In yeast-inoculated coffee fermentation it rose 2- to 10-fold over the control, and the difference remained after roasting. This route from phenylalanine, the Ehrlich pathway, works the same way in sake and in coffee.

⚠️ Both are coffee research, not statements about sake.

Formed as yeast metabolises leucine. The higher the rice polishing ratio and the fermentation temperature, the more is made.

Esterified, this becomes isoamyl acetate — the banana note. It is where the fusel alcohols and the esters join up.

★ Every sake carries it above the threshold (even the bottom of the reported range sits higher). So it is never a question of present or absent, only of how much: the source treats it as sake's ground note. In quantity it turns marker-pen.

★★ Coffee fermentation makes the same compound by the same route. In washed coffee fermentations inoculated with yeast (Hanseniaspora uvarum / Pichia kudriavzevii), isoamyl alcohol is reported to rise 2- to 10-fold over the control, and the difference remained after roasting. This route from amino acid to fusel alcohol, the Ehrlich pathway, comes up in other studies too as a central route to aroma in coffee fermentation. The same mechanism that makes the ground note of sake is turning in a drink that is not alcohol at all.

⚠️ Coffee research, not a statement about sake.

Formed when unsaturated fatty acids oxidise and cleave.

One of the compounds identified as contributing to the fishy aftertaste in dried scallop soaked in red wine. ★ It is not an aroma the wine carries — it appears on the food side, once wine and seafood meet.

Formed when unsaturated fatty acids oxidise and cleave.

A product of the same pathway as hexanal. One carbon longer, so the fatty side is said to come forward ahead of the green — ★ But that sentence is an inference from the neighbouring compound, not the words of anyone who smelled it.

Formed when unsaturated fatty acids oxidise and cleave.

Formed when unsaturated fatty acids oxidise and cleave.

Formed when polyunsaturated fatty acids oxidise and cleave.

A form that keeps two double bonds. Within the fishiness, it carries the impression closest to fish oil itself. ★ In the wine-and-seafood experiment it was not detected at all in iron-free model wine, and appeared only in the iron-bearing red (0 → 4.2 μg/kg). Where the other compounds were already present and simply rose, this one is created from nothing.

Formed when fatty acids break down. In sake it arises late in koji making, when linoleic acid undergoes oxidative cleavage by the enzymes of the koji mould, contributing to the smell of koji.

An example of the limits of "they share a compound, so they pair." The same molecule flips meaning depending on what sits around it. In raw shiitake it is held to be the single most important aroma compound by OAV. ★ In the experiment on fishiness from pairing wine with seafood, it rose roughly sixfold in dried scallop soaked in iron-bearing red wine (0.09 → 0.52 μg/kg), while its counterpart alcohol did not rise significantly. ★ It also appears as a metallic contributor in oxidised pork liver, where it is placed on the branch that oxidised arachidonic acid takes.

Formed when fatty acids break down. In sake it arises late in koji making, through the enzymes of the koji mould.

The counterpart to 1-octen-3-one, though the ketone is reported not to arise from oxidation of this alcohol. It is sometimes listed among the components of fishy odour. ★ However, in the experiment on fishiness from pairing wine with seafood, this compound did not rise significantly (8.3 → 10.0 μg/kg). What rose roughly sixfold in the same experiment was the ketone. Lumping the C8 compounds together as "part of the fishiness" hides this difference; the -one and the -ol behave differently.

Formed by the metabolism of yeast and lactic acid bacteria - within this family, an exception in being fermentation-derived.

It sits here by the shape of the molecule (a ketone), but the way it forms does not fit the family description. In sake it is treated as a fault.

★ In wine there are situations where having little of it works on the side of showing something. Red wines made without sulfite are reported to be lower in both acetaldehyde and diacetyl than conventionally made ones, and that difference is held to affect how fresh the wine feels.

⚠️ That report is on wine and does not cover sake.

★ In coffee fermentation too, in a treatment co-inoculated with lactic acid bacteria and yeast, the closely related 2,3-butanediol (made by the bacteria) was reported to contribute to the aroma. In the yeast-inoculated treatment 2,3-butanedione, that is diacetyl itself, was detected. The thread that it turns up where lactic acid bacteria are present runs through sake and coffee alike.

⚠️ That is coffee research, not a statement about sake.

Appears during fermentation one step short of ethanol, and either stays or increases later through oxidation. In sake it rises when alcohol is added while intermediate metabolites are still abundant.

It sits here by the shape of the molecule (an aldehyde), but the way it forms does not fit the family description. The same treatment as diacetyl.

★ In sake it is called kiga-yoshu, a light smell said to suggest wood, grass and green apple.

★ It has the property of binding with sulfite, and that is where it gets interesting. In wines with sulfite added it accumulates in the bound form; in wines without, there is nothing for it to bind to.

Where it goes instead is colour. Unbound acetaldehyde gets used as a bridge joining pigment and tannin. Two things then happen at once: the concentration falls and the colour deepens toward purple (the colour difference exceeds the human perceptual threshold). One property accounts for both the aroma side and the colour side.

Bordeaux reds made without sulfite are reported to be lower in both acetaldehyde and diacetyl than conventionally made ones, and that difference is held to affect how fresh the wine feels. A compound of the kind where absence is what shows something.

⚠️ Everything above about sulfite and colour is wine research. It does not cover sake. The threshold, content and name on the sake side come from the National Research Institute of Brewing report on the smells of sake and where they come from. What holds for wine does not necessarily hold for sake.

Lactic acid bacteria work on a fatty acid, and yeast trims it into a ring.

Detected at the sniffing port as "sweet, honey". One of the compounds present at higher concentrations in entries flagged for a spicy, 4VG-like character. ★ Those entries came from a new-sake competition — they were not aged sake.

A fatty acid is transformed and closes into a ring.

Detected in sake GC-O as butter, baked. On the beef side it is listed among the compounds correlating strongly with sensory scores for wagyu aroma. It appears on both sides of the table.

⚠️ It is not the one that was higher in the sake flagged as spicy / 4VG. The lactones showing significant differences were gamma-nonalactone, gamma-dodecalactone and dehydromevalonic lactone; this compound was detected in both the flagged and the control samples. So it is no grounds for saying that this aroma and 4VG turn up together.

A fatty acid is transformed and closes into a ring.

In the worked examples of a patent, this group of compounds was rated as "sweet-smelling" above 100 µg/L and "like coconut or vanilla" above 300 µg/L. ⚠️ This is a patent, not peer-reviewed literature.

A fatty acid is transformed and closes into a ring.

One of the compounds that correlated strongly with sensory scores for wagyu aroma. ★ The source is a study of beef; it says nothing about any commonality with the lactones in sake.

A fatty acid is transformed and closes into a ring.

One of the compounds that correlated strongly with sensory scores for wagyu aroma.

Formed when ferulic acid from the raw material is transformed by microbes. In smoked foods it transfers from the smoke itself.

Among entries flagged for a spicy, 4VG-like character, this was the compound that differed most from the controls — roughly sevenfold on average. In katsuobushi it is counted among the main compounds behind the smoky aroma. It appears on both the drink side and the food side.

★★ The cleanest demonstration that a particular microbe makes a particular compound . In a study that inoculated nine different starter cultures separately into coffee fermentation, guaiacol was produced only in the treatment inoculated with Bacillus subtilis. The authors singled it out as a marker that this organism had been at work. It supports, from the other direction, this map's placing of guaiacol on the microbe-made side.

⚠️ That is a study of coffee, not a statement about sake. Whether the same organism does the same thing in sake cannot be drawn from this source.

Formed when contaminating bacteria and wild yeasts decarboxylate the ferulic acid in the rice. Sake and shochu yeasts do not do this.

Found in junmai sake among others. In entries flagged for this character, at least 70% are estimated to sit above the threshold. ⚠️ At judging competitions this aroma is treated as a fault.

Said to be formed by reduction of 4-vinylguaiacol.

★ Its presence in sake has itself been confirmed. In a survey of competition entries it was detected in only a very small number of samples. Where 4-vinylguaiacol turns up routinely, this one rarely appears.

⚠️ The threshold is unconfirmed. The route by reduction of 4VG is known in wine, but has not been confirmed in sake.

Formed as compounds from wood, or phenolics from the raw material, are transformed.

★ Under ambient storage it becomes detectable somewhere between 11 and 15 years. In young ginjo it sits below the threshold. Aged samples span a wide range, from traces up to 1727.5 µg/L, with barrel-stored sake highest. One of the few compounds where "aged sake means vanilla" can be pinned to a number of years.

There are two routes. One joins acetaldehyde with an acid formed from the breakdown of an amino acid (threonine); the other is the reaction between amino acids and sugars (the Maillard reaction). Both proceed over long storage.

★ Mean concentrations are 0.1 without hineka, 0.5 with hineka, and 9.8 µg/L in long-aged sake. The share of samples above threshold is 5% for commercial sake with hineka and 73% for long-aged sake. So the caramel note is a feature not of aged sake but of long-aged sake.

★ Although it sits in this family, it is not a compound made by the Maillard reaction alone. A family name lets one route stand for the group; it does not mean there is only one.

Formed in the reaction between amino acids and sugars (the Maillard reaction).

A principal aroma compound of soy sauce. The soy-sauce note that appears in sake is thought to come from its structural resemblance to sotolon, and from both liquids carrying the same kind of compound — products of a reaction between amino acids and sugars.

Formed as sugars change under heat and long storage.

★ The concentration does climb in aged sake, yet even in stored samples the OAV never reaches 1. A useful reminder that "more of it" and "you can smell it" are not the same thing.

The route differs by type of sake. In long-stored sake it comes from the breakdown of an amino acid (leucine); in namazake it comes from enzymatic oxidation of the isoamyl alcohol upstream of it.

45% of sake showing hineka, and 93% of long-aged sake, are above threshold. It is listed among the compounds contributing to a honey-like aroma.

★ One of the main compounds of hineka (the other is DMTS). The sharp smell that comes out when namazake is left at room temperature is also this compound. ★ The same molecule appears both in ageing and in the deterioration of namazake, but the routes are different. What this family holds is the long-storage route.

Born in the reaction between amino acids and sugars under heat (the Maillard reaction). It comes out in quantity when high temperatures are applied, as in roasting and baking.

★ The card that brings the relation between fermentation and roasting onto this map. In coffee fermentations inoculated with yeast, 2-methylpyrazine and 2,5-dimethylpyrazine have been detected in the roasted beans. The authors suggest that the organic acids increased by fermentation may feed the formation of pyrazines and furans during roasting, but ⚠️ this is a hypothesis, not a demonstration (the authors themselves write that further work is needed).

★★ There is also a report that the length of the fermentation moves the amount of pyrazine. In a study varying the days of anaerobic fermentation, short fermentations (2-8 days) were high in pyrazines, pyrroles and furans, and correlated with a different set of compounds than long ones (10-20 days). In another study, pyrroles and furans serve as a marker for telling processing methods apart. A compound made by heat, whose amount is nonetheless set by the fermentation conditions before it — an instance of the material at the entrance deciding the aroma at the exit. ⚠️ The former study, however, does not make clear whether it measured green or roasted beans. Nothing is asserted here on that basis.

★ On the food side, ethyl dimethylpyrazines are listed among the roasted notes of katsuobushi. The same reaction makes the aged aroma of sake, the char of cooking and the roast of coffee — a compound that embodies the build of this family.

⚠️ For pyrazines in sake, no supporting material is held yet. What is written here is what is known from katsuobushi and coffee.

Formed by the breakdown of an amino acid (methionine). A sulfur-containing aldehyde.

In sake it contributes to the smell of koji; in shiitake it is among the compounds with the highest FD factor. ★ The phrase "cooked potato" comes from the shiitake study — the sake literature does not use it.

From contamination by hiochi bacteria, or carried over from persimmon tannin.

★ Among the fault aromas on this map, its threshold is fairly high (in mg/L). It works differently from compounds like DMTS that tell in trace amounts: it only shows once it has clearly increased.

Formed when the koji is contaminated by Bacillus subtilis.

Formed as the TMAO that fish already contain breaks down over time.

Weakly alkaline, so on meeting an acid it turns into a salt and stops evaporating. That is why squeezing a lemon, or pouring something high in acid alongside, actually works. Saltwater and deep-sea fish start with more of it; freshwater fish with less. ★ Fishiness is not one single thing. The lipid-oxidation route is not stopped by acid.

Formed during fermentation as yeast metabolises sulfur-containing amino acids (the early to middle moromi). Also formed when heat breaks down cysteine and cystine.

★ Pause before counting this as a fault in a bottle on the shelf. It is perceptible in fermenting moromi and in freshly pasteurised sake, but the source notes it is scarcely detectable in commercial product.

Formed when methionine breaks down under heat and light. A component of hinataka, the sunstruck smell.

★ This is the one that really is a thiol — it carries the sulfur-hydrogen pair. It still sits apart from the tropical 3MH and 4MMP, because what separates them is not whether sulfur is present but how they arise: those are cut free by yeast from precursors sleeping in the raw material, while this appears when methionine breaks apart under heat and light.

⚠️ The reference standard is ethyl mercaptan, but the one said to predominate in sake is methyl mercaptan.

Formed by the breakdown of a protein containing a compound produced when old rice was fumigated.

In sake this sits on the fault side, as the smell of old rice. It is also listed among the compounds of fishy odour, and in katsuobushi it barely changes through the smoking process — a compound that appears on both sides of the table.

⚠️ Note the period. The route the source gives for sake runs through a compound formed when old rice was fumigated with methyl bromide — a practice now banned in Japan.

Formed during storage, when a precursor left behind by the yeast during the mash breaks down.

★ The lead role in hineka, the smell that ordinary commercial sake picks up. 65% of sake flagged for hineka and 93% of long-aged sake sit above the threshold. The threshold is so low that a trace decides the impression.

★ Its precursor, called DMTS-P1, is reported to come off the pathway by which yeast rebuilds methionine. The seed of hineka is already in the sake when it leaves the tank — storage only unlocks it.