Green Coffee Storage:

A Factor That Ought Not To Be Overlooked


by Chris Lee from Tea & Coffee Trade Journal Feb 1999


This article is aimed at large roasters, brokers, exporters and other producers. By dealing with long-established and respected specialty coffee brokers, Sweet Maria's circumvents many of the problems stated herein ...well, if they are doing there job, then it shows in the cup quality of the samples. Coffee properly milled, rested in pergamino, shipped and stored will cup well will cup well too. And since everything we carry is based on the cupping of samples taken from the bags in the warehouse from the actual lot of coffee we will later receive (this is all verified and guaranteed by the broker), there's really no "crapshoot" involved with our coffee purchases. But this article points out all the places along the route from produced to the customer where things can go wrong.


Imagine this: As a roaster and coffee buyer you've spent months identifying green coffees and coffee estates that meet your strictest quality standards. You've cupped each of the coffees you plan to buy a dozen times. You've cupped those coffees at different temperatures. You've put those coffees into the blends you plan to use them in and then cupped them again. Finally, you've roasted them to different degrees of darkness, to ensure that you have gotten the right coffee. You've also done your research on the growing conditions. You know how well the trees are taken care of and how often farmers are pruning their trees. You are aware of the elevation the coffee is grown at, and you know whether the coffee is shade grown. You're also aware of whether the coffee is sun-dried or machine dried, and you've ensured that clean water is used in the processing mill. In other words, you know everything there is to know about the coffees you are about to purchase right down to the subspecies of tree that the fruit is being picked from. Having done your research, you eagerly await the arrival of your new crop coffees. When, at last, the coffees arrive at your warehouse, and you begin roasting, you are angered and dismayed to discover a past crop taste in your coffee that certainly was not there when you first cupped the sample. "What went wrong?" you wonder. Well, it just may be a case where a flavor taint results from improper methods of green coffee storage.

A Factor That Ought Not To Be Overlooked

With coffee being the second most traded commodity in the world, you might think that the coffee industry, especially the specialty coffee industry, would have green coffee storage down to a science. The truth of the matter, however, is that storage and shipping conditions can still make a big difference in the overall cup quality of a coffee. "It surprises me a lot," says one roaster, "you would think the storage companies would have this stuff down cold." There are varying opinions among coffee storage experts both about what is in fact necessary for storing green coffee, and about what the ideal conditions for storing coffee are. We did, however, find that there is a consensus on three variables that we should be concerned about: humidity, temperature, and warehousing conditions.

Humidity and Temperature

Humidity is a critical variable. Green coffee leaves the processing mill with a 12% moisture content. In theory, to maximize its flavor profile, the coffee should be dropped into the roaster when it still has a 12% moisture content. In practice, however, there are many variables to consider before this may be accomplished. In conditions of low humidity, the coffee may lose moisture, and in conditions of high humidity, the coffee may gain moisture.

"The duration of how long green coffee can be stored varies depending on geography," explains Bob Fulmer of Royal Coffee in Burlingame, California. "Places with relatively low level of humidity have short storage times. Low levels of humidity suck the moisture out of green coffee. (The coffee loses it moisture to the surrounding environment). A customer in Denver has us hold their coffees and ship only a two weeks' supply at a time."

Coffee that has absorbed too much moisture, particularly from exposure to humid environments for long periods of time, may take on a "fermented, moldy type of overtone in the cup," says Jay Isais of the large roaster/retailer chain, Gloria jean's. If the coffee is stored in too humid of an environment, and gains moisture, the appearance of the coffee "would be darker" continues Isais, and if the moisture level is much above 12%, the coffee "feels soapy." Isais notes one caveat: "Too much moisture, in certain cases can be okay. If the coffee is freshly milled, the taste in the cup will be fine, but you will have more shrinkage." "The coffee's origin makes a difference as far as moisture loss is concerned," explains Steve Sloat, president of the Annex warehouse in Oakland, California. "Coffees from the Far East pose a particular problem. There are longer transit times and there is a more drastic swing in humidity. Also, there is no ventilation in the container." These conditions facilitate condensation and cause the coffee to absorb moisture. "Coffee arrives at 152.3 net and one month later is 149.9 net" says Sloat. "You can lose up to 1.5% of the total weight of the coffee within the first month."

Fulmer also focuses on another issue related to the role of humidity in the shipping of green coffee. "What specialty roasters should ask is how the coffee has been handled at source, especially prior to shipping," warns Fulmer. "In higher elevations, where the coffee is milled, humidity is low once the coffee is milled , and loses its pergamino acts as a barrier to prevent moisture from entering the bean and also from leaving the bean] it can then re-absorb moisture." Coffee may leave the processing mill at 12% moisture, but if the coffee isn't shipped problems may result. coffee's journey from the processing to the shipping port brings it conditions of low humidity and mild temperatures to conditions of high humidity and high temperatures. If the coffee sits at port for too long (for example, the coffee missed the boat), then the coffee will re-absorb the moisture of its environment, at times up to 13% moisture. When this happens, as Fulmer explains, "The coffee gets bleached out. It takes on a baggy, "past-crop" like flavor in the cup. it loses acidity, loses its edge and takes on more neutral characteristics. Like past crop coffees, the color of the bean fades as well. This is the most common green coffee storage problem that we have seen."

The pergamino also serves as a protective barrier against both moisture loss and the absorption of excess moisture. "If coffee is harvested in the winter, and is then s-milled in April, but sits in port through July before being shipped, the coffee can take on a past crop flavor," says Fulmer. Conversely ,if the same coffee sits in pergamino at higher altitudes, and isn't milled until November, the coffee, which will maintain a constant moisturee level, may actually improve in quality over what it was in April.

While our experts could not agree on a specific level of humidity that is ideal, just about everyone suggested that a moderate level is appropriate, and that stable levels are essential. "It is the change in temperature and humidity that can cause condensation," says Doug Eland, of Eland, a Toronto-based warehousing company. Winter months pose a particular concern for Eland as coffee travels from the hot climates near the equator to cold temperatures of Toronto. "Condensation is a big problem when coffee is shipped from producing countries." As the coffee sits at the terminal for a long time, the temperature inside the container remains warm. However, the outside environmnent is cold, and condensation results. "Even if the containers are lined with paper, water drips from the ceiling into the coffee," says Eland. Ultimately, the moisture will permeate the bag and fermentation will result.

There are ways to rescue the coffee from those conditions. "It's not so much the moisture that damages the coffee," explains Isais, but "the effects of the moisture that cause damage." Eland, in fact, describes a method where bags are spread out onto the floor and dried if the condensation was not extreme. Other times the coffee needs to be "re-bagged" and "reconditioned." If a disaster occurs and coffee gets wet, Isais, interestingly enough, suggests dumping the coffee into the roaster right away before the effects of the moisture have time to do harm. "Even when green coffee gets wet, if the coffee is roasted within a few hours, then it is okay. However, if the coffee sits around, then it will get moldy."

The temperature of coffee during shipping as we have just seen, as well as storage, can have an effect on the quality of green coffee. Probably the most important thing to consider is how stable temperatures are since quick changes in temperature cause condensation. The effects of quickly changing temperatures are similar to those of changing levels of humidity. "Ventilation and insulation (in the warehouse) are important," says Fulmer, "a good draft and good circulation are needed to keep humidity and temperature levels constant. As heat rises, good air circulation can prevent temperatures from rising."

Kevin Kelly, president of Port Cargo in New Orleans, has a simple motto: "If it's comfortable for people, then it's comfortable for the coffee. If people aren't going to like the conditions, then the coffee is not going to like the conditions either." In New Orleans, conditions of 100% humidity and 95'F are not uncommon. During those conditions Port Cargo is able to achieve 70% humidity by storing coffee in well-insulated buildings that contain wall, ceiling and floor fans for air circulation. The insulation and fans not only keep employees working in conditions of relative comfort, but also keep the coffee happy by maintaining more stable temperature and humidity conditions.

Just as roasters may urge their customers to keep their freshly roasted coffee out of the freezer, so too may they want to ensure their coffee is not exposed to freezing conditions during shipping. "In transit, or in a warehouse, the coffee must not be allowed to freeze," Isais exclaims. "The net result [of frozen coffee] is a dehydrating effect, which takes the edge out of the cup and makes the coffee less intense. It is similar to past crop coffee in the sense that the green coffee loses its color and takes on a straw character in the cup. I haven't tested the moisture level of green coffee that has been frozen, but I would assume that it loses some [moisture]." Additionally, when coffee loses moisture it not only looks and tastes different, but it feels slightly different as well. "When you drop it on the counter," Isais explains, "the sound it makes is not as dense [as the sound it would make if the moisture level was appropriate]."

Our experts could not acquiesce on specific temperature levels that are ideal for green coffee storage. Eland suggests a 50OF 70OF range; Sloat suggests that 60OF may be the practical ideal, but that cold storage, 40OF 50'F may be the most ideal. Doug Carpenter, president of Ronnoco Importing, the most specific of the people I spoke with, asserts that 72OF and 50% 55% humidity has been ideal for storing green coffee in his warehouse in St. Louis, Missouri.

Warehousing Conditions

When asked about the ideal condition for storing green coffee, warehousing conditions were often first thing many experts thought of Steve Stewart, president of Gulf Winds International, a logistics provider to the coffee and tea industry based in Houston, says that concrete structures that have concrete flooring serve several purposes. Concrete structures not only keep temperatures more constant, they also facilitate cleanliness and pest control. "Cleanness is paramount!" exclaims Steve Stewart. "Our warehouse is subject to the same standards of cleanliness that a restaurant is." Air quality inside the warehouse is important as well.

"Coffee is susceptible to foreign odors," says Eland, "we segregate it from other products." Kelly made a point about owning all of the space his company warehouses in. "We have our own quality control person, who is responsible for checking the rodent stations and fire sprinklers on a weekly basis." Certainly, no roaster wants to think about mice wandering through their prized Sumatra, but it is something shippers and storage companies must actively take action to prevent. While the jute bags coffee is shipped in may facilitate "breathability," as Isais points out, Eland warns that the jute also -makes ideal nesting for mice.

Climate Control Projects One of the most ambitious efforts at controlling the environment that green coffee is stored in is taking place at Ronnoco. Ronnoco's "Climate Control Room" has been used f now for the past four years, and has t focused on controlling temperature, s humidity and air circulation. A desire to preserve the ideal flavor profile of their green coffees for their customers provided the impetus for investing in climate controlled storage. As Carpenter explains, "We started by asking ourselves, 'How do you handle specialty coffees, which come in once a year, so that you preserve their flavor profile for the entire year?' "Their premise was that by preventing green coffee moisture loss they would also prevent degradation in flavor profile. In order to determine the best storage conditions for preventing moisture loss, they began by conducting research about the best conditions for storing wine. After some trial and error, they eventually decided to set their climate controls to 72F and 50 55% humidity. In order to test their climate control room, they stored four different kinds of coffee, both inside and outside of the climate control room, and cupped the coffee at regular intervals. "Can we visually see a difference [in the color of green coffee stored under climate control conditions] and taste a difference?" 'Carpenter asks rhetorically. His response: "Certainly." in fact, Carpenter, reports that after six months of storage, the coffee that has been stored outside of their climate control room begins to fade in color, lose its acidity, and lose its original flavor profile and flatten out. Coffee stored in the climate control room, on the other hand, maintains its flavor profile for 12 months, enabling Ronnoco to maintain the flavor profile of coffees that only come in once a year. Based on their findings, Carpenter says that they are considering "changing the entire warehouse into climate control."

Carpenter hopes that Ronnoco's innovative climate control methods opens a dialogue about the ideal storage conditions for green coffee, and believes that their efforts to date are only a "starting point." He further noted that Ronnoco's tests took place on the cupping table, and that he hopes scientific studies will introduce empirical evidence in the future. Certainly, if climate control storage allows coffees to retain their content throughout the course of a year, and therefore retain their flavor profiles for the course of the year, then more climate control projects are warranted. "I would expect more people to use climate in the future," predicts Carpenter.

What Is A Roaster To Do?

Like all other aspects of sourcing green coffee, assiduous cupping routine will lessen the chances that improper green coffee storage will have a detrimental impact on the quality of one's coffee. Damage from excess condensation can be detected during "subject-to-arrival" samples. Sloat says that some larger roasters also take moisture readings. Generally, this is done so the roaster has a better idea of how to roast the coffee and how much shrinkage to expect, but could also alert the roaster to storage or shipping problems that affected the coffee's moisture content. Roasters are also advised to keep their coffee on pallets. "Green coffee can absorb moisture from concrete if the green coffee is not kept on pallets," cautions Isais.

Sloat and Fulmer, who both have businesses in the San Francisco Bay Area, say that the west coast, and specifically Northern California, probably has the best natural conditions in which to store green coffee. Air-conditioned storage spaces are available in areas where humidity and temperature are concerns, but representatives from both Depuy and Port Cargo in New Orleans say that very few, if any, customers are willing to pay the price for that option. When considering the air-conditioned or refrigerated storage option, perhaps another factor to examine is humidity. One of Carpenter's tests involved storing green samples in the refrigerator. Strangely enough, less than a year later, the coffee took on a past crop flavor. "The refrigerator was a 'dry cold,' and had a humidity level that might have been as low as 5%," reported Carpenter. He also reminds us that roasters need to tailor climate controls to the climatic conditions of the region in which they are storing coffee.

With so man aspects of coffee production under close examination for the purpose of maximizing quality, it only seems logical to consider the conditions under which green coffee is stored. Green coffee storage may not be down to a science, but the insights of many experts lend credence to the view that green coffee storage is a salient factor in determining cup quality. Storage of green coffee should not be viewed as a passive, or neutral gap that occurs between the time it is imported and when it is roasted. Rather, it is an active process where factors of humidity, temperature, time and other ambient conditions play a dynamic role in either preserving or altering the original taste of a particular coffee.


Chris Lee, currently a research assocciate and market analyst for Castle Communications, was formerly product supervisor for Spinelli Coffee Company.


Note: this article was scanned using OCR software so there may be errors and misspellings due to this fact.


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