Monsooned coffee

Where it is practiced

The Malabar coast, in India, on a strip running from Mangalore in Karnataka to Kozhikode, the old Calicut, in Kerala. The area filed with the Indian geographical indication is “India (Karnataka and Kerala)”. The treatment is not done on the plantations. It is done in the green coffee preparation factories, the curing works, set up on the coast. The coffee itself comes from several producing regions of the country. The season is narrow: from June to September, during the southwest monsoon, when the winds are saturated with humidity. The verifiable chronology is short. The Coffee Board writes that monsooned coffee has been classed as an Indian specialty since the 1950s. The first Indian standard for grading monsooned coffee appears in 1967: the foreword to the 1981 revision says so itself, and dates the first revision to 1975. An article in the Coffee Board's journal dates the launch on the international market to 1972. The two geographical indications, arabica and canephora, were registered on March 28, 2008 in the name of the Coffee Board, under numbers 85 and 114.

The principle

Monsooning ferments nothing. It rehydrates. The other processes in this series work on the fruit, that is, on the pulp and on the mucilage, the layer of sweet flesh stuck to the parchment. Here, there is no fruit left. The bean is already dry, already hulled, already sorted. The substrate is the seed itself.

The starting mechanism is physical. A coffee bean is hygroscopic: it exchanges water with the air until it reaches equilibrium. Indian cherry coffee, that is, coffee dried as whole cherry, is packed at 11.5% moisture. The air of the southwest monsoon is close to saturation. The bean therefore absorbs water vapor, in stages, and its content reaches 14 to 15% in about ten days. It swells, to nearly double its size: the wording is that of the Indian standard, in both revisions read. Its color turns pale yellow, sometimes straw white, and the standard makes this shift part of the definition of monsooned coffee.

What follows is chemical, and it is enzymatic. Water awakens hydrolysis reactions, that is, the splitting of molecules by water. A comparison by gas chromatography and liquid chromatography, between monsooned arabica and unmonsooned arabica, measures three changes. Chlorogenic acid, which is astringent, falls markedly: it is hydrolyzed into caffeic acid, which is bitter. Methoxypyrazines, responsible for the vegetal, green pea smell of green coffee, decrease. 4-Vinylguaiacol and isoeugenol increase: they existed in part as glycosides, that is, bound to a sugar, and monsooning releases these precursors. The measured result is a dominant spicy note.

The authors looked into what cleaves chlorogenic acid, using gamma irradiation at 5 kilograys. On monsooned beans, the cleavage occurs whether the irradiation comes before or after monsooning. On irradiated unmonsooned beans, it does not occur. They conclude that the cleavage is enzymatic and not radiolytic, that is, made by enzymes present in the bean and not by the radiation itself. This is a point of mechanism, not a guarantee in the cup.

Another study, one of whose authors also signed the previous one, followed the composition week by week during monsooning. Tannins fall below the detection threshold. Proteins and reducing sugars increase steadily. Phenolic compounds fall in canephora and rise slightly in arabica. The bean is therefore not just wetted and swollen: its composition is reworked during the twelve to sixteen weeks that the process lasts.

Four weeks, and the Aspergillus take over

This sheet describes monsooning as a controlled moisture uptake under the wind laden with monsoon, and it treats with caution the question of what happens biologically during those weeks. A numerical element is missing, and it is useful because it gives a clock.

Hackler and Särchen write that the microbial population of the bean changes during monsooning and that species of the genus Aspergillus dominate after approximately four weeks. They rely on the work of Tharappan and Ahmad, published in 2006.

Three consequences can be drawn from this one sentence, and they do not all point the same way.

The first is that monsooning is indeed a biological process and not only a physical one. The process could be described as a simple rehydration followed by a swelling and a discoloration of the bean, and that would be incomplete: a population settles in, and it settles in a precise direction. It is not a fermentation flora in the sense of the tanks, since the substrate is no longer mucilage but a bare bean, and the available water, even after rising, remains well below that of a fresh fruit.

The second is that the direction taken is that of a genus several of whose species produce ochratoxin A, starting with Aspergillus ochraceus and Aspergillus carbonarius. It must be added at once that the genus Aspergillus is vast and that most of its species produce nothing toxic; the source cited does not go down to the species level, and nothing here allows us to claim that a monsooned coffee carries more mycotoxins. What this datum establishes is that the process deliberately sets up the conditions of a genus that is watched elsewhere, and that the question of analytical control therefore arises more sharply for this coffee than for another.

The third is a clock, and it is the most directly useful piece of information. If the shift toward Aspergillus occurs around the fourth week, then the duration of monsooning is not a continuous variable: there is a before and an after, and the process descriptions that give durations of six to seven weeks place the coffee several weeks on the late side of that shift. This provides a testable hypothesis to explain the characteristic profile of monsooned coffee, thick body, collapsed acidity, earthy and woody notes, without having to attribute it vaguely to humidity.

The caveat is the same as for the other second-hand data: the account available gives neither the number of lots, nor the identification method, nor how dominance is defined, whether in colony counts or in relative abundance of sequences. Tharappan and Ahmad will need to be read before the four weeks can be carried as a numerical landmark.

Sources for this passage: Hackler and Särchen, chapter 5, p. 79, after Tharappan and Ahmad, 2006.

The sequence

1. Starting material. Only whole-cherry coffee, that is, dried by the dry process, is admitted. For arabica, only grade “A”, the one whose beans are retained by a 6.65 mm screen. For canephora, only grade “AB”, retained on 6.00 mm. The geographical indication file lays down the rule without giving the reason.

2. Entry moisture. The green coffee standard sets 11.5% at bagging for arabica cherry as for canephora cherry, with a tolerance of 0.5 point. It is the gap between this figure and the exit target that defines the quantity of water to be taken in.

3. Place and season. The work starts in the coastal factories during the active southwest monsoon, from June to September. The air must be close to saturation: a bean takes up water only if the air contains more than it does.

4. Spreading. A layer 10 to 15 cm thick, in a shed open on the sides, ventilated, with a cement floor. Thickness governs how far air penetrates the mass. It appears as such in the foreword to the standard.

5. Raking. About every three hours. The standard itself gives no frequency: it only writes that the beans are raked from time to time. The three-hour figure comes from the geographical indication file, which explicitly links this action to the uniformity of the beans' exposure to the wind. The standard, for its part, names the corresponding defect: the imperfectly monsooned bean, which has kept the characteristics of green coffee.

6. Ten days. The moisture of the bean reaches 14 to 15%. That is above the final target. Everything that follows no longer serves to wet, but to equalize.

7. Bagging. Jute bags filled halfway, unsewn, stacked four high, rows spaced apart. The stated aim is to let air circulate freely around each bag.

8. Emptying and rebagging. Once a week. The file gives two reasons: preventing mold and obtaining even monsooning. The standard describes the same operation as equalizing moisture between beans.

9. Total duration. From 12 to 16 weeks. The figure is that of the foreword to the standard, in the 1981 version as in the 2019 one.

10. Exit control. Moisture must be between 13.0 and 14.5% by mass on leaving the warehouse, measured by the method in annex A of the green coffee standard. The range has been unchanged since 1981.

11. Finishing. Polishing to give a slight sheen, screen grading, classing, then hand sorting. Four categories are removed:

• beans that stayed hard and unmonsooned
• blacks
• cut beans
• the triage

12. The six grades of the 2019 standard, with the screen and the share retained:

• Monsooned Malabar AAA: 7.50 mm, 90% retained
• Monsooned Malabar AA: 7.10 mm, 90% retained
• Monsooned Malabar A: 6.70 mm, 75% retained
• Monsooned Malabar Arabica Triage: 6.00 mm, 90% retained
• Monsooned Malabar Robusta AA: 7.10 mm, 90% retained
• Monsooned Malabar Robusta Triage: 6.00 mm, 90% retained

13. Defect ceilings. No more than 2% by mass for Monsooned Malabar AA, no more than 3% for Monsooned Malabar Robusta AA. The 1981 standard tolerated 4% for Monsooned Malabar AA and 5% for Monsooned Robusta AB, a grade that has since disappeared. On defects, the specification has therefore tightened. On screen size, it has loosened: Monsooned Malabar AA had to clear a 7.25 mm screen in 1981, it clears 7.10 mm in 2019. The 2019 foreword explains the reworking of the grades by alignment with the geographical indication.

14. Storage and shipping. Fumigation during storage against weevils. Rebagging in 60 kg jute bags at the time of loading. Containers are fumigated according to the requirements of the importing country. Shipments are concentrated in December and January.

What it gives in the cup

What is measured. A chromatography comparison between monsooned and unmonsooned arabica, published in 2003, finds three effects:

• methoxypyrazines, which carry the vegetal smell of green coffee, fall
• 4-vinylguaiacol and isoeugenol, which carry the spicy note, rise
• astringent chlorogenic acid falls markedly, hydrolyzed into bitter caffeic acid

The authors sum up the result as a dominant spicy note. It is a measurement of compounds in the bean, not a rating by a panel. A 2009 study compares monsooned coffees and ordinary Indian coffees. It finds significant differences on eight parameters:

• moisture
• density
• pH
• color
• soluble solids
• phenolic compounds
• caffeine
• chlorogenic acids

Only the abstract of this study could be read. Neither the direction nor the size of the differences is given there.

What is claimed. The Coffee Board, in its two geographical indication files, describes body, low acidity, a round, sweet and mellow taste. Its website speaks of a moldy flavor and a syrupy flatness recalling aged coffees, and of use in blends to soften harsher, more acidic coffees. These wordings come from the applicant for the geographical indication and from its institutional website. They are descriptions, not trial results.

What was not found. No blind sensory trial comparing the same lot before and after monsooning. The drop in cup acidity, which is the most cited promise, has only indirect support: the measured drop in chlorogenic acid. A lower chlorogenic acid is not the same thing as a cup rated less acidic by a panel.

In roasting. A trade article from India cites a 2002 study on three points. Monsooned beans slow down their roasting under isothermal heating at 200 degrees. They lose 20% of their mass when roasted in air. The target color is 59 to 61 on the Agtron scale. The bean arrives swollen, less dense and moister than normal. That is enough to explain why it does not behave like an ordinary green coffee. This source is second-hand: the original work was not read.

What goes wrong

Mold is the central risk, and it is structural. A coffee is considered ready for long storage at 12% moisture, that is 0.60 water activity. Monsooned coffee is kept above that, between 13.0 and 14.5%, and spends twelve to sixteen weeks in air close to saturation. The process therefore deliberately sets up the conditions that the rest of the industry spends its time avoiding.

The measurements confirm it. A week-by-week follow-up during monsooning shows fungal populations that peak between the fourth and seventh week. The dominant species recorded are Aspergillus niger, Aspergillus tamarii, Aspergillus candidus, Penicillium and Absidia heterospora. Another study compares monsooned and unmonsooned coffees. On the monsooned ones, it counts around a hundred million colony-forming units of bacteria per gram. A colony-forming unit is a living cell able to multiply. Fungi are a thousand times fewer there, around a hundred thousand per gram. The major fungal species recorded are Aspergillus terreus, Aspergillus restrictus and Aspergillus ochraceus. The authors themselves conclude that monsooned coffee may carry heavier contamination by spoilage molds, and in particular by mycotoxin-producing species.

This point deserves to be stated plainly. Aspergillus ochraceus belongs to section Circumdati, Aspergillus niger to section Nigri. These are the two sections that produce ochratoxin A in the coffee chain, a mycotoxin that is toxic to the kidney. A nuance is needed: in section Circumdati, the strongest producers are Aspergillus westerdijkiae and Aspergillus steynii, and in section Nigri it is Aspergillus carbonarius. The species found on monsooned coffee therefore produce ochratoxin, but they are not the worst of their section. Finding these species does not prove the presence of the toxin either: not all strains produce it, and production requires precise conditions. The risk is nonetheless not theoretical, and no ochratoxin A measurement on monsooned coffee has been found.

This is what explains the rhythm of the work. Three actions come back constantly:

• rake every three hours
• fill the bags only halfway
• empty and rebag every week

The geographical indication file describes them as measures against mold and for uniformity. These are not decorative traditions, they are the safeguards of the process.

The defects named by the standard number four.

• The imperfectly monsooned bean: it has kept the characteristics of the corresponding green coffee. Cause: uneven exposure, a layer that is too thick or insufficient raking.
• The malodorous bean: bad, moldy or foreign smell when the sample is sniffed.
• Blacks and browns: more than a quarter of the surface discolored. The standard specifies that this category includes stinkers and sours, that is, over-fermented beans and sour beans.
• The triage, the low category, which must be free of blacks, browns, stinkers and sours.

Insects follow moisture. The Coffee Board states that monsooned coffees are fumigated to prevent weevil attack, and that the containers are too, at departure.

There remains the risk of place. The geographical indication file asserts that trials carried out inland, under controlled conditions, did not produce the character of monsooned coffee. The 1981 Indian standard says the opposite, however: monsooned coffee can also be produced under high, controlled, artificially created humid conditions. This sentence disappeared from the 2019 revision. Neither text publishes data.

Benchmarks

• Moisture before and after11.5% at entry, 13.0 to 14.5% at exit
• Moisture peak14 to 15%, reached in about ten days
• Layer and raking10 to 15 cm thick, rake about every 3 hours
• Total duration12 to 16 weeks, from June to September
• Monsooned Malabar AA grade90% retained on a 7.10 mm screen, 2% defects at most
• 2023 exportsabout 5,870 t of all monsooned grades combined, of which 4,243.5 t of Monsooned Malabar AA