Storing and shipping green coffee

A dry seed that keeps exchanging water

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The FAO's guidelines on mould put the behaviour in two figures. In store, coffee goes on drying if the air around it is drier than about 60 per cent relative humidity, and begins to absorb water if the air is more humid than about 80 per cent. Because coffee can sit in store for a long time, the document says, even very slow changes become a problem.

It lists the ways dry coffee gets wet again: moisture creeping from damp floors and walls, leaks and wind-driven rain, still air, and dry coffee being blended with wet. It adds one that is less obvious. A lot is stable while its water is evenly spread, and a difference in temperature across a stack is enough to make the water move within it.

The trade handbook describes the same property from the other side: coffee is hygroscopic and settles towards a balance with the air around it. It reports a relative humidity of 60 to 65 per cent as the figure generally given for storage.

The balance also moves with temperature. A 2025 study that measured it on Colombian parchment coffee at 25, 35 and 45 degrees Celsius found that, over most of the range it covered, the same coffee settled at a lower moisture in warmer air of the same relative humidity. That was parchment coffee of one variety, not hulled green coffee, and the study gives its results as curves, so it shows the direction and supplies no figure for a warehouse. The guide to buying and judging green coffee says more about what it measured.

Jute, liners and sealed bags

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Jute is the traditional sack, and the handbook gives the reason: it lets moisture escape, which lowers the risk of mould. The same openness is its weakness. Coffee in a woven sack follows the air of the warehouse and takes on its smells.

The handbook describes a recent trend, especially for higher-quality coffee, towards high-barrier packaging, and pictures the usual form: a jute sack with a plastic liner inside. It attaches a caution that is easy to miss. A barrier stops water passing through the bag, but temperature differences can still move water about inside it.

Jute brings one hazard of its own. The fibre is softened with oil before spinning, and the handbook records cases of coffee contaminated by hydrocarbons from that oil. An international specification for sacks used with food exists for this reason, and it includes a smell test.

Three studies of packaging, and where they disagree

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The largest study read was run by Colombia's coffee research centre and published in 2025. One washed coffee of the Castillo variety was kept for 365 days in eight kinds of packaging, two of natural fibre and six of plastic, at four places: a cold, high site, a hot and humid lowland site, a warm site and a cold room. A panel of five certified tasters scored it at 60, 120, 240 and 365 days. At the cold, steady site, at about 10 degrees Celsius, every package held its score for 240 days. At a year, four of the plastic packages still held it, while both fibre sacks and the other two plastic ones had fallen from about 81 points to between 53 and 63. At the hot, humid site the score declined after 60 days whatever the coffee was packed in. In the cold room it held to 240 days in everything, and to a year in three of the plastic packages.

The moisture readings show what the fibre was letting through. The coffee went into store at about 11.8 per cent. In fibre it rose to around 15 per cent at three of the four places, and in plastic it stayed near 12 everywhere. At the hot site the fibre sacks gained very little, ending at about 12.5 per cent, and the score fell anyway. The authors conclude that the place explained the changes, and that fibre sacks suit short periods, which they put at under 60 days.

A study published in 2023 kept Guatemalan coffee in jute and in a sealed polymer bag at minus 10, 10 and 20 degrees for up to a year, with five certified judges tasting it every three months. Coffee at 20 degrees aged fastest and the two colder temperatures performed similarly well; at those, the scores stayed in the specialty range for six months and were close to it at nine. The authors report no clear difference between jute and the sealed bag overall, though the sealed bag held water activity steadier. They report that the washed and the natural coffee differed more than the two kinds of bag did, but the two came from different farms, so that comparison cannot separate the process from the farm.

An earlier paper from the same group, published in 2022, reports on coffee from the same two farms kept as 100-gram samples in small jute and sealed bags in chambers at minus 10, 5, 10, 18 and 20 degrees. Its tasting results add one thing: cold slowed the decline and did not stop it. The coffees began at 86 and 86.8 points. After three months most still scored above 80, with the 18 and 20 degree chambers lowest. After twelve months the highest scorer, the natural coffee in a sealed bag at minus 10 degrees, scored 81.1, and the washed coffee kept at 18 and 20 degrees had lost about ten points. The same paper reports the caffeine measured in the roasted coffee falling by about 40 per cent over the year at every temperature. Caffeine is a stable compound, as its authors themselves say, and CoffeeHQ reads a loss of that size as more likely to lie in the measurement than in the coffee. None of that paper's chemical figures is used here.

A third, from Thailand in 2022, held 250-gram samples of green arabica at 30, 40 and 50 degrees for twenty days and measured the oxidation of its fat. Higher temperature meant more oxidation, and the hermetic bag kept the measures lower than plain polyethylene or woven plastic. Nobody tasted that coffee, and it began unusually dry, at about 7.5 per cent moisture.

Put together, the three agree on temperature and differ on packaging. Heat ages green coffee in all of them. A sealed bag made a clear difference at the cold site in the Colombian study by the end of a year and none at the hot one, and in the 2023 study its authors saw no clear difference. These are three coffees in three sets of conditions, so it is a pattern to hold loosely.

What ageing is, chemically, as far as it has been measured

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Underneath the packaging studies is a slower question: what is changing inside the bean. The best-documented answer is in the oil. A 2006 review of coffee lipids reports that a fat-splitting enzyme was active in every green coffee its authors tested, including coffee ten years old, and describes their own experiment on a Colombian coffee kept for eighteen months. Free fatty acids, released as the oil is broken down, about doubled at 25 degrees Celsius in coffee at its original moisture of 11.8 per cent, hardly moved in coffee dried to 6.2 per cent, and rose most in coffee moistened to 13.5 per cent. At 12 degrees the rise was small even in the moist coffee. At 40 degrees it was marked within three months in all but the dried coffee. Changing the atmosphere in the store made no apparent difference.

A study of 2020 pushed robusta much harder, holding green beans in open paper bags in hot-air incubators at 40, 50 and 60 degrees for twenty days. Free fatty acids rose from 1.2 to between 2.1 and 3.3 milligrams of potassium hydroxide per gram of oil, more at each higher temperature, and the indices of oxidation rose with them. The beans also dried out, from about 7.9 per cent moisture on a dry basis to between 3.8 and 1.9, so heat and drying acted together and the experiment does not separate them. Nobody tasted the coffee. Its authors fitted the rise in one index to predict shelf lives of weeks at those temperatures. Such a prediction describes the conditions of the experiment; it is a way of ranking temperatures, and it is not carried across to an ordinary warehouse here.

So two of the three things a warehouse can control, temperature and the coffee's moisture, have each been shown to change the rate of one chemical process, and the third, the gas around the beans, did not in the one experiment that tried it. None of this was scored by tasters: the review's one remark on the cup is that the storage at 40 degrees was abandoned after a year because the brews were not worth discussing, and the robusta study tasted nothing. It is offered as the mechanism most likely to lie behind what the packaging studies found, and that is a suggestion, not a demonstrated link.

What the guidelines ask of a warehouse

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The FAO document describes a sound store without making it an expensive one: a high ceiling and plenty of moving air, a cement floor with a damp-proof course, a site that does not flood, and a roof and windows that keep water out. Stored coffee is to be kept out of direct sun and away from anything that heats one side of a stack, because that is what sets water moving.

Sacks are kept off the floor on pallets and away from the walls, stacked so that air can pass. Records are kept of when each lot arrived and in what condition. Nothing that is not food is stored alongside, because of taint.

One instruction doubles as a diagnostic. The guidelines say the coffee weevil can survive only in coffee too wet to store, so finding it means wet coffee is present somewhere, and the remedy is to deal with the moisture as well as the insect.

How a container comes to drip on its own cargo

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The sequence is the trade handbook's explanation of condensation in a shipping container. The FAO guidelines give a container load as 18 to 22 tonnes; the handbook puts the average at about 21.

What shippers do, since condensation cannot be prevented

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The handbook's position is blunt: apart from shipping coffee that is dry enough, condensation cannot be avoided, and all that can be done is to stop the water reaching the beans. It says coffee above 12.5 per cent moisture should never be shipped, and in the next breath that 12.5 is not a level every buyer accepts, only the point at which the risk becomes unacceptable. Many contracts now state a maximum moisture on arrival.

The measures it and the FAO guidelines describe are physical. Containers are checked for holes, smells and damp floors; the handbook has the inspector stand inside with the doors shut, looking for daylight and smelling for chemicals. Bags are kept off the steel with cardboard or thick paper, a layer goes over the top of the stack to catch drips, and bags are stacked so that they do not leave open vertical channels for air. Bulk coffee travels inside a sealed liner kept clear of the roof. Loading is done under cover and not long before the ship sails.

On drying agents the two documents are cautious. The guidelines say packets of silica gel are sometimes used and that their efficacy is unknown. The handbook says desiccants should be used only with the receiver's permission, and that many receivers do not allow them at all.

It also says where the damage usually happens: at origin, when containers are packed too early or badly lined, or just after unloading in winter.

Ageing, and the words for it

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The Colombian study's introduction describes what badly stored coffee tastes of, citing earlier work: woody flavours, low acidity, a weak body and a dirty, heavy aftertaste. The trade handbook treats age as a commercial fact: in a passage about credit it says coffee is usually best marketed while fresh and that storage beyond the usual selling season is not advised.

Two things complicate the picture. The handbook says a period of resting after drying gives green coffee a longer life and sometimes reduces a greenish taste, and that the practice is becoming less common. And the International Coffee Organization's moisture rule carries an exception for speciality coffees that traditionally have a high moisture content, naming Indian monsooned coffee; the resolution does not say what makes them so. Age and damp are usually a loss. The rules allow that they are not always treated as one.

Why there is no shelf life on this page

CoffeeHQ explanation

No document read gives one, and the studies explain why none could. In the same experiment the same coffee kept its score for a year in one place and began to lose it after two months in another. A figure in months would be true of one warehouse.

For the same reason no storage temperature or humidity is offered as a target. The humidity and moisture figures above are the named documents' own, set for safety against mould. Freezing green coffee, vacuum packing at home and how long a small bag keeps in a kitchen are not covered: nothing read addresses them.

How green storage differs from keeping roasted coffee is CoffeeHQ's summary and not a finding: roasted coffee stales in weeks through loss of aroma and oxidation, while green coffee changes over months and mostly through water. The guide to staling covers the roasted side.

What to do next

• Green coffee: what it is and how it is judged — Where the moisture and water-activity figures come from, and why a meter reading is less simple than it looks.
• Why coffee goes stale — The roasted side of the same question, which runs on a much shorter clock.
• Coffee grading, system by system — The moisture limit sits inside the same international target as the defect count.
• Colombia — The country whose research centre ran the year-long packaging study, and whose climates it was designed around.