Arroyo’s Oidium

[If you are a distiller, make sure you know about the birectifier]

In Arroyo’s 1945 Studies on Rum, he presents two different paths for symbiotic fermentations to produce full bodied rums. The first path uses a bacteria while the second path claims to use an Oidium (a mould), but recent research shows it may actually turn out to be a type of alt yeast.

Where did he get the idea anyhow? Arroyo has pretty much no bibliography other than the classic rum texts, but appears to cast a wide net and is well versed in emerging ideas in bio technology. He mentions finding this “mould” on the sap of a tree in a shade grown coffee plantation (shade grown coffee is really interesting). He does not say exactly what specific tree so it is hard to pin down because shade grown coffee plantations are known for spectacular diversity.

Besides, a mould of the Imperfecti group, Oidium Suaveolens, was also found very well adapted for the production of a special type of heavy rum.

Pages later he tell us more:

Another special type of heavy rum was produced during our studies and experiments. This time the raw material used was sugar cane juice. The yeast strain used was No. 764 and the auxiliary ferment was a member of the Fungi Imperfecti, Oidium Suaveolens. The Oidium was found and isolated by the writer from the sap of a tree much used in Puerto Rico for shading coffee plantations.

A study of this Oidium revealed that it would grow very fast in cane sugar juice media with the production of a thick film over the surface of the liquid. It was further discovered that it hardly touched the sugars in the medium, but that it was a good producer of esters and organic acids from the proteins of the raw material. A fragrant odour, very similar to that of ripe apples was the predominant aroma observed.

This Oidium was used as an auxiliary ferment for the production of heavy rums from sugar cane juice in two different ways: (a) a sterilized sugar cane juice mash of from 12.0 to 15.0 per cent total sugars was inoculated firstly with the Oidium culture. After the Oidium film was formed on the surface of the medium it was allowed to act up it for a period that could vary between 24 and 72 hours or more if desired. Then the mash was inoculated with an active footing of yeast No. 764, and the fermentation was carried to completion. (b) In the second method the yeast was allowed to operate alone in the substrate, and towards the finishing of the alcoholic fermentation the Oidium culture was inoculated. The Oidium fermentation was allowed to act then for variable number of hours, as desired.

Both methods worked satisfactorily in the creation of a new variety of heavy rum out of sugar cane juice mashes; but the rums obtained differed somewhat in each case, those produced by method (a) being of intenser taste and higher aromatic tone.

Many databases exist like the Global Biodiversity Information Facility that have listings for the organism, but they contain no spelled out history of discovery that may elude to where Arroyo got the idea (A Russian database points us to Geotrichum Frangrans which can be purchased here from the American Type Culture Collection ATCC). Arroyo did name the organism correctly as Suaveolens, and calling it an Oidium may point to the Russian biologist Krzemecki who possibly discovered it in 1913 based on language included in the GBIF entry. Arroyo may have also been hip to the organism by reading the mycologist Christine Marie Berkhout. Or maybe Arroyo never read her 1923 doctoral thesis that (quoting wikipedia) was later described as marking “the beginning of the rational systematics of the anascosporogenous yeasts” (I’m way out of my depth, but trying to bridge the gap between Arroyo’s mould and the recent researcher’s recategorization as yeast. The difference between a mold and a yeast is that molds grow with multi celled hyphae while yeast’s are single celled).

We are building up to some links to great modern research papers, but we should pause for a moment. The whole point of this exercise is to (a) celebrate how fucking cool Arroyo was, (b) help modern rum writers who may talk to producers and find evidence of these techniques used in a production, (c) help new producers jump off on this, and lastly (d) celebrate the contemporary researchers who will help us bring more of Arroyo back to life and create new exciting styles of rum.

Contemporary research on this organism and my realization that Arroyo may have been incorrect about it being an Oidium are lead by Thomas Petit and Eric Grondin working on the island of Reunion off the coast of Madagascar.

This brief info graphic style paper by Petit mentions participation in a European COST (cooperation in science & technology) bioflavour project. After scouting yeasts, Suaveolens, came up as their most significant flavor producer, specifically producing the valuable ester, ethyl tiglate (a known semio-chemical #pheramone).

To back track a bit, from an old text that summarizes abstracts, we can glean a little bit of the interest from 1923.

A study of Ester-Forming Yeasts.
Ulrich Weber, Biochem. Ztshr., Berlin 129:208, April 19, 1922.
Experiments are described that sought to determine the conditions under which the formation of fragrant esters takes place in some lower fungi. The question was dealt with by physiologic experimental methods. There were employed Willia saturnus Klöcker, Oïdium suaveolens Krzemecki and Siachsia suaveolens Linder. These organisms were raised in pure cultures in nutrient glycerin and mannite solutions under different conditions.

Results showed: In the observed yeasts and imperfecti fungi the ester odor typical for normal cases is not developed under all conditions. Cases occur in which, in spite of the most abundant development, no ester formation takes place, as in the case of growth in a carbon dioxide atmosphere. Esters are formed only when the simultaneous fermentation of carbohydrates assumes the role of sugar fermentation and liberates the energy requisite for the decomposition of albumin. Addition of alcohol enables a qualitative alteration of the ester odor to be attained. The employment of different nitrogenous nutrient media achieves an alteration of the odor only when other amino-acids are thereby presented simultaneously. Following addition of leucin a distinct odor of amylester is perceived. The ester odor of the species here investigated, which is always observable under normal conditions, is therefore capable of being influenced experimentally both qualitatively and quantitatively, as it is possible to alter both the character of the odor and also to prevent its occurrence in spite of the best development of the fungus.

The Yeast, A Taxonomic Study has some useful information on understanding what exactly the Saprochaete of Saprochaete Suaveolens entails.

Swedish Wikipedia provides a great bibliography.

And finally we come to a few spectacular modern research papers:

14 thoughts on “Arroyo’s Oidium

  1. Matt from Tamworth Distilling here. Great post. I’ve been peripherally interested in bioflavorants for some years now and always saw the potential for their parent organisms’ use in spirits.

    Especially cool to see that ethyl tiglate is a natural product. Wasn’t aware it was anything but artificial. I dreamed of a practical prep for ethyl tiglate in spirits a few years back that started from angelica extracts. Haven’t found time for proof of concept yet. Buying some yeast seems way more elegant.

    All this should get the the next generation increasingly excited about the full gamut of “jungle fermentations” that carry loads of biodiversity to the table. Are components of rum oils microbiologically derived in these manners, rather than from the canes themselves? Carotenoid bio-decomposition is known to lead to a spectacular array of interesting chemicals ( and it’s produced abundantly by some fairly ubiquitous yeasts. Harnessing the chemical ecology of these natural processes would surely make Arroyo smile.

  2. Thanks for commenting Matt.

    As far as I can tell, rum oils come from splitting glycosides found in the substrate. It isn’t easy to do and needs lots of optimized variables which is why they typically never have their potential reached in rums these days. Enzymes produced by alt yeasts like schizosacharomyces pombe may be best suited for the job.

    Some day I’ll be in a better position to bring more of this to life. Right now I’m taking a detour design and manufacturing.

  3. True, pombe seems to have the right stuff to preserve glycosides through fermentation for subsequent hydrolysis during distillation. But there are certainly less linear possibilities for transformation of feedstock components into non-ester aromatics as well. I haven’t been able to get remote journal access to work lately, but there are some great articles on production of alluring volatiles via straight thermal degradation of carotenoids in acidic, aqueous mediums — including reference to detection of one of them, 1,6,6-trimethyl-1,2-dihydronaphthalene (fruity, tropical), in Australian rums. This appears w/o additional exposure to carotene-degrading bacteria that could potentially prime the pot for a multitude of alternative reaction pathways. Hope to follow up on some of this after I get a few projects finished up on the farm. Cheers.

  4. my understanding (which has lots of room for correcting) is that glycocides are split during fermentation instead of being preserved so they can be harvested during distillation. unsplit, they discarded with the non-volatile fraction. this may be why a resting period after fermentation ends benefits heavy rums. it is possible to split them during distillation but that is not the most significant stage.

    the Australian rums have never impressed me and a few older examples I’ve come across have a peculiar noxious character. I’ve never found out what it is attributed to. I just requested a document you may be referring to and I think in its bibliography it has a few references that relate specifically to Australian rum. I’ll try and request those when I get the article. if you ever have a citation you want pulled, feel free to forward it, the librarians are very good to me.

  5. It’s odd that there’s so little information on the specific identities of glycosidic aromas, considering how long they’ve been known. The interesting thing is that aroma active molecules are often volatile enough to co-distill earlier in a distillation run. If I recall correctly, so-called “rum oil” is one of the last things to come over — well into the steam distillation stage? I’d think this implies that it’s a fairly high MW, hydrophilic molecule that may happen to have a very low threshold of perception, or that it is created by the increased heat and TA of a post-ethanol wash. The end of a long distillation can approach 50% reduction in volume and accompanying doubling of reaction rate due to increased acidity. Add to that the ~5-7C increase in temperature and you could be looking at 4-fold rate increase of glycoside hydrolysis. After all the junk comes over, that could be enough to create a fraction enriched in beneficial aromas w/o flaws.

    Have you seen this freely available shochu paper?

    As indicated, even the fairly large and partly oxygenated beta-damascenone (a personal favorite) with a boiling point of something like 200C begins coming over pretty early in the distillation of shochu. If it was all produced during fermentation, it seems it may begin distilling over earlier and probably be done by the steam stage. (It also shows that their shochu yeast has some beta-glucosidase activity, but that particular yeast seems to metabolize the damascenone during fermentation. I’m not familiar on how pombe utilizes its glucosidase…)

    It all makes for great theoretical banter. Apologies that it can quickly become so abstract and disconnected from rum in particular. I’m not as familiar with the rum literature as you, though I really wish there was sound analytical info on rum oil in particular.

  6. I’ve written this response a few times only to screw it up and lose all my citations, etc… So this is quick and hopefully somewhat easy to apply to our previous thoughts before I forget entirely.

    Those precise chemical names you were cross-referencing with “rum” can confound searches via syntax errors, etc. Much to the chagrin of the IUPAC, searching the common name for TDN, “ionene”, provides a fair report of its known contributions to rum. Since my academic credentials have been officially revoked again, I’ll just drop URLs both relevant and related to the unsubstantiated possibility that formation of low-volatility, low threshold-of-perception chemicals contribute to so-called “rum oils”:

    1) Initial searching revealed this GC/MS document that seems to be focusing on recreating authentic rum flavors. They detect what they call an abundance of hydrocarbons and perform syntheses to confirm the structures of what they found: TDN, TTN, and isomers. They continue on to speculate that these are among ESSENTIAL chemical contributors to an authentic rum flavor.

    2) This paper indicates the detection of new hydrocarbons via chromatography and NMR/IR analysis of Jamaican rum. Trimethylnaphthalene (TDN-like) derivatives were detected alongside trimethylphenylbutanoids, and their origin is speculated to derive from exogenous carotenoids included in distillation.

    3) Following the lead of trimethylphenylbutanoids (and their isomeric tendencies toward TDN & company), I came across this paper indicating its role as a potent odorant (0.04 ppb threshold!) that is derived from glycosides of white wine grapes. Not rum by any means, but precedent set for their appreciation?

    4) Further reading of reference #2 indicates that megastigmaenones were also detected in their Jamaican rum. Megastigmaenones are something of a broad class of compounds and can be isomeric in a bunch of ways (even damascenone & ionone are megastigmaenones, I’ve come to appreciate). They are responsible for tobacco-like aromas as well as representing characteristics of both passionfruit and osmanthus. These aromatics are both caroteinoid-derived as well as oak-derived, thus present in new-make as well as aged spirits. Also detected in dried fruits, likely by various oxidations of endogenous carotenoids.

    5) The formation of aromatics in tea is possibly a good model for similar outcomes in other food products that are processed under heat for extended durations. This paper focuses largely on the enzymatic formation of precursors in tea (not that it’s impossible in raw materials other than tea) and also elaborates on non-enzymatic mechanisms (photo-oxidation, auto-oxidation, thermal degradation) for their formation.

  7. great insights. now that there are some more firm targets, we will have to work on making it actionable and weaving it into a story. drinkers should know their spirits are product of a quest.

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