Processing coffee

The way coffee is processed sets the style of coffee that will leave the roaster for further stages. This stage that referred to as ‘wet milling’ contains all the various steps that occur from picking, until ‘dry milling’ and then loaded into bags for transportation. Processing practices vary from between regions and farms, because of the limitation of economy or available resources or simply because they have their own style. For example, in Burundi farmers hand over their picked cherries to government washing stations for further processing. In other countries and other farms all the processing is done by the farmer. This seemingly routine stage in the development of the coffee is so important and open up new expressions of flavor in coffee and distinct the coffee’s natural profile in each farm with different processing facility. Irrespective of how meticulously the coffee has been harvested, underripe and overripe cherries are inevitable. Only perfectly ripe fruit contains the most sucrose and results in the sweeter cup. Over or underripe fruit will like any other fruit result in a bad tasting product and this is not something that a good roaster can cover up.
Screening is conducted in a water tank where overripe and underripe fruit along with leaves and sticks will float. Fruit sinks to the bottom and become ready for the next stage. Becoming whether the finest specialty coffee known to man, or the most deplorable coffee fruit destined for jars, coffee beans need to be removed from the fruity shell and slimy cherry mucilage. This is done in two ways: wet (or washed) processing or natural (dry) processing. Some countries or regions use one method over the other and some use a combination of both techniques which called pulped-natural or semi-washed. Naturally processed coffee is a relatively straightforward process, as all its various layers are left intact. The fruit is sent to the patio or a raised drying bed for drying and, where relevant, ripening. This process can take many weeks and care must be takeد to avoid mold and rot, but some natural fermentation is normal. After the fruit has fully dried, it’s dark, shriveled form must then be hulled(peeled) to reveal the beans patiently waiting inside. Brazil is the spiritual home of naturally processed coffee, where the economic culture of coffee has bred a ‘pick now, sort later’ approach, with the like of Sao Paolo State and the Cerrado region naturally processing over 90 per cent of their coffee. Naturally processed coffee is non-interventional, self-contained and, well, natural, which gives the resulting coffee its dirty, heavy and wild – often to the point of wacky – fruit notes. The capricious brilliance of dry processed coffee can yield inconsistent results, however, and the clarity of the cup can be lost. It is for this reason that some roasters choose to avoid it all together.

Washed Coffee

Washed Coffee, also known as wet-processed coffee, sees the whole cherry get pulped, either mechanically (by what is effectively a large blender) or by jets of high-pressure water. Either way, the cherry is split and squeezed, forcing the beans though a separate aperture. If you really wanted to, you could pulp cherries by hand, but from personal experience I can tell you that it is slow, messy and thankless. Pulping only deals with the soft flesh of the cherry – there’s still the mucilage that coats the bean to contend with, and like the last slimy bits you get on a peach stone, it turns out it’s highly resilient stuff. Removal of the mucilage is ordinarily done by way of fermentation, which in fact refers to a broader process of microbial growth rather than the action of yeast and sugar in the absence of oxygen (as is the case with brewing).
During its time in fermentation tanks, the pectin in the mucilage is broken down through the activity of enzymes, and the environment becomes more acidic. The length of fermentation depends on a number of factors, not least of which is temperature and the volume of coffee being processed. Fermentation is not just about removing mucilage, though; it’s also an exercise in coffee flavor development, and, when timed well, it can produce a level of clean acidity that natural coffee can only dream of Coffee. Despite the positive reputation that wet processing possesses, it is no assurance of quality. Fermentation can be unpredictable, particularly since it relies solely on micro-organism that are naturally present on fruit and/or in the water. There are, of course, numerous variations of wet processing specific to different countries and regions, too. In Kenya, for example, it is common for two fermentations to take place, with an intermediate wash in the middle; this has been cited as one of the reasons for Kenya’s incredibly bright and fruity coffees.

Pulped Natural Coffee

Pulped natural coffees are recognized under a variety of other titles, including ‘semi-washed’ or ‘semi-lavado’, and the delightful-sounding ‘honey-process’. For a coffee farm, this marriage of methods neatly combines the economic benefits of the natural process with some of the speed of the washed process — you find better body than some washed coffees, but more clean and crisp character than with natural coffee. The process starts out in the same way as wet processing: the coffee is first pulped to remove the skin and flesh. As with washed coffee, the mucilage remains attached to the seed, but instead of being sent to fermenting tanks for removal, the beans skip straight to the drying phase. Drying pulped natural coffee is particularly challenging, as the moist and sticky environment is the perfect setting for rot and decay. Mechanical dryers don’t work, as the mucilage sticks to the hot surfaces like glue, so the coffee is dried on raised beds or raked over large patios in a process that takes one or two weeks. During pulping, the farmer can also choose to remove some, or most, of the mucilage from the seed before drying, which speeds things up even more. It also gives the green bean a lighter color, and takes the character of the coffee further in the direction of a washed coffee. Mechanical demucilagers are becoming more commonplace and are effectively an extension of the pulper, whereby they depulp and strip the mucilage through the use of rough bristles or through the use of water pressure. Critics of these types of machines claim that foregoing the fermentation process of a fully washed coffee denies the coffee some of its clarity and acidity. Seeing as the amount of mucilage left on the seed is so important to the final character of the coffee — steering it in the direction of washed or natural coffee traits — this scrubbing or ‘shaving’ process is now loosely graded in the context of honey-processed coffee. ‘Black honey’ retains most of the mucilage before drying; ‘red honey’ removes some; and ‘yellow honey’ removes all, or nearly all of it. Costa Rica is of a good example of a country that has embraced this kind of processing with gusto. Many farmers there are investing in small demucilagers to fine-tune their processing methods. This become particularly interesting when a single estate releases a crop that has been processed in two or more ways, because it allows us humble consumers to draw taste comparisons between the different methods.


Whether undergoing wet processing, the pulped natural or natural method, eventually the coffee must experience a drying process that reduces the moisture content of the bean from 40 percent down to around 10-12 percent. This is a process that requires constant attention, since the warm, moist piles of beans need to be regularly turned to avoid the development of mold and bacteria. Airflow, temperature, humidity and light must all be taken into account. Patios are the oldest, cheapest and simplest form of coffee drying, where the coffee is spread a couple of inches deep and raked hourly to provide equal airflow and light to all the beans. One of the useful traits of the patio is its ability to soak up the heat during the day, which it continues to release overnight, thus providing quite stable and consistent drying conditions. Raised beds, also known as African drying beds, are becoming increasingly popular around the world. The advantage of the bed is the improved airflow that it offers, meaning that the coffee does not need to be turned as regularly. Some beds, in countries such as Colombia — where the weather is changeable — also have plastic covers (like a poly-tunnel) that protect the coffee from rain, but still allow sufficient airflow. Some hot countries, specifically those in Africa, have been forced to develop multi-stage drying processes that aim to limit the effect of the midday sun. These include such practices as moving the coffee from shade to light and piling it in mounds to moderate the evaporation of water. The general consensus is that the best coffee is produced when the rate of drying decreases near the end of the process. As you might expect, there is also more industrial means of drying coffee, but these are not as commonplace as one might think. Once again it boils down to economics, where the cost of a mechanical dryer simply cannot compare with the price of cheap labor and a little bit of time. However, there is no escaping the fact that mechanical dryers at their best offer a much more consistent product, especially in areas of unpredictable weather, in a fraction of the time usually taking just 12-24 hours from start to finish. After drying, the coffee bean is still encased in its brittle parchment shell and will remain a relatively stable product, protected from external flavors and susceptible only to the dangers of extreme temperature and moisture. Beans are usually rested at this stage, for at least a few weeks, but only up to three months.

Left overs

Perhaps you’re wondering what happens to all discarded coffee fruit? The coffee bean itself accounts for only around 20 per cent of the wet weight of the whole coffee cherry, so there is quite a lot of waste. In some countries, the wet pulp is recycled as fertilizer, but disposal of the vast quantities of waste water that are used in this process, and the subsequent pollution caused by coffee cherry mucilage are problems that are consistent all over the world. Some producers have taken to drying the cherry flesh into a product called cascara. Resembling a dried cranberry, cascara can be brewed into a kind of fruit tea that tastes a little like high-octane rosehip tea, due to caffeine present in the fruit.

Milling And Transportation

To complete its journey, the coffee must be dry-milled to remove the parchment, then graded for quality, checked for defects, sampled, packed, and exported. The size of producer’s farming operation and its financial circumstances, the degree to which the producer processes the coffee, customs in the area, geographical limitations, presence of co-operatives and the legal structure within the country, are the factors important in this process.
What is parchment coffee? Dried beans that are still encased in their endocarp, or parchment layer, while still in this form, the coffee is a mixed bag of large and small green beans, cracked beans, twigs, leaves and probably a bunch of other things besides and it still requires milling, screening, grading and repacking. Parchment coffee is worth a lot less than prepared green beans. Growers sell they product either to a dry mill, which does the job of removing the parchment and sorting the coffee, an exporter (responsible for shipping the coffee) or a middle man, or even two middle men (known colloquially as coyotes); often these guys hang out at bus stops and collect bags of parchment coffee from small farms, pay for them, then transport them to the mill or the exporter for sale. Some growers rest, mill and sort their coffee before selling to exporters, but that is quite rare outside of the biggest farms. There are even some growers who handle their own export, too, but this is even more scare, and not without its headaches from an importer/roaster’s perspective.
In some countries, there may also be a co-operative in the mix, often representing over 1000 small growers. Co-operatives will sometimes do the job of wet milling and drying the coffee beans; some will take storage, before shifting the parchment coffee on to an exporter, while others may have dry-milling facilities and indeed, perform the role of exporter. Traders can buy up stocks of coffee, add it to their inventory, then sell it on to the next man for their inventory, then sell it on to the next man for an increased price. Brokers basically do the same thing but without ever taking physical possession of the coffee; they are in effect just connecting sellers with buyers and skimming their cut off the top. Many speciality roasters have now established direct-trade relationships with farms to better understand where their coffee has come from and to ensure the farm receives fair payment for their work. It is more about transparency, when a farmer, miller, exporter, importer, and roaster all work together towards a more sustainable industry model.


Once the coffee arrives at the mill, it is first passed along a vibrating platform that removes any dry debris that may have been loaded into the bag. Next it is hulled of its parchment in a large blender like contraption, and it’s at this stage that the green bean itself is now finally visible. Coffee sizes are measured in fractions of an inch, but commonly referred to as a single number: e.g. 16/64 inch is simply a size 16. Particularly small beans may be rejected and sold at the local market. Once sorted, samples will be taken and visually examined for defects, then roasted in a small ‘sample roaster’ to assess the quality of a finished cup. The mill will be looking for such things as evidence of coffee weevil activity, manifested by small boring holes in beans. The sheer quantity of small growers means that some exporters and buyers will sample roast, grind, brew and cup up to 1000 samples of coffee a day. Some of these samples may be identified as being of especially high quality, and the goal of the exporter will be to separate these from the lower-quality samples that may be blended together for bulk sales.
Transportation Green coffee has, in the past, always been transported in the familiar 70-kg/155-lb jute, hessian or burlap sacks and they continue to be the bag of choice for most exporters (and many a bean-bag manufacturer) as they are cheap, renewable and, practically speaking, easy to take samples from. The downside of jute is that it provides absolutely no protection from water, and as such, meets only the most fundamental requirements of a bag. Green coffee, while much harder than roasted coffee, does age and deteriorate over time and the jute sack does little to prevent this. In recent years, a couple of newer options have become popular with roasters that pay particular attention to the quality and freshness of their greens. One of the much-heralded alternatives is the vacuum sack, which effectively removes all of the air from around the product and protects it against moisture and exterior odors. There are other plastic options that have made an appearance recently, too, such as the products created by US company Grain Pro Inc., which offer some of the benefits of vacuum packing, but without the need of specialist equipment.


Truthfully, though, decaffeinated doesn’t have to mean bad. It’s just a fact of life that it generally is. Most baristas apply less care and attention to making decaffeinated espresso, and certainly most roasters consider its processing and packaging an afterthought. Better quality decaffeinated coffee is becoming more available, however, made from fresh, good-quality green beans and roasted in the correct manner, and these rare examples we find that flavor has not been compromised at all. These days, decaffeination is still conducted before the coffee is roasted and generally removes 90-95 per cent of the caffeine from the product. Priority number is to remove as much caffeine as possible from the coffee, while priority number two is to leave behind components of the bean that are necessary for flavor development during roasting. The Swiss water process is a little more gentle, and involves first soaking the beans in water to open up their cell structure. The beans are then washed with a water-based liquid that also contains a concentrated extract of green coffee – the theory being that any positive attributes that are removed by the water are immediately replenished by the extract. At this stage, the CO2 is in a supercritical state, meaning that its temperature states it should be a gas, but its pressure forces it to behave somewhere in between a gas and a liquid. The caffeine dissolves into the CO2 over a few hours, then the pressure in the system is reduced, allowing the CO2 to evaporate, stripping the caffeine away in the process.
On a final note, in 2008, a naturally caffeine-free species of coffee, Coffea Charrieriana, was discovered in Cameroon, which could be a huge development.

Instant Coffee

Contrary to what you might think, instant coffee is made from real coffee. It generally tastes nothing like the real thing, but once upon a time, like any other coffee drink, it was a seed on a green tree. It’s the arduous inorganic process that instant coffee undergoes that strips away any hint of nuance that may or may not have once existed in what was most likely a poor and wretched coffee bean. A brewed cup of coffee is a delicate thing; its complex aromatics are fleeting, and its merits remain for only the briefest of moments. The advantages of instant coffee are undeniable, though. The coffee would always be consistent, foolproof to prepare, easy to adjust according to strength preferences and it would never go stale — not to mention the fact that it would take up much less space in the kitchen. That, no doubt, was the plan when David Strang launched Strang’s Coffee, the first soluble coffee granule back in 1890. Strang used a ‘Dry Hot-Air’ method to evaporate the moisture out of the brewed coffee, leaving behind a crusty coffee residue that could be broken up into mostly soluble nuggets. One such product was George Constant Washington’s ‘Red E Coffee’, which launched in 1910 and dominated the market until the arrival of Nescafe. Perhaps the biggest name in instant coffee, Nescafe, was launched in 1983 after the Brazilian government approached the Nestle food company, seeking a solution for its huge surplus of coffee beans. The product itself was a combination of sugar and dried coffee residue, and was an immediate success, thanks to largely to World War II, as it became a hit with the military for its longevity and convenience. After the war, it became a staple product in kitchen cupboards around the world, over one-third of all the coffee imported into the USA being turned into instant. After World War II, high-vacuum freeze-drying was introduced, which meant that coffee could be dried at a lower temperature, more quickly, meaning this flavor was better preserved. This technology, along with spray drying, is how instant coffee is made today. In all methods the coffee is first roasted and ground. Next water is pumped through a series of 5-7 judge percolation columns. Each column contains coffee at varying stages of extraction, and as the water passes from the freshest through to the oldest, the temperature decreases, ensuring that nothing is left behind. Spray-drying entails moving a superfine mist of coffee concentrate through a column of hot air – think hairspray and hair dryer. The mist is so fine that the tiny coffee particles dry into big piles of brown flour. Freeze-drying is slightly more sympathetic to the coffee. The concentrate is cooled down to -40°C/-40°F usually very rapidly (in the region of 1-2 minutes). The very low temperature means that the coffee concentrate is below its triple point — the lowest temperature possible for solid and liquid concentrate phases to co-exist. The dried coffee will still contain around one per cent moisture, but compared to most earthly objects that is very low indeed, and the cause for its fragile and brittle nature. It’s this low water content that also gives instant coffee one of its greatest strengths: preservation. It’s not clear whether it is the technology used to manufacture instant coffee, or the quality of the coffee in the first place, which is responsible for the insipid instants that we know and recognize. The experience with freeze-dryers leads us to think that there is perhaps a future for genuinely great instant coffee.
Right now, though, the speciality coffee movement and the supermarket shelf are at odds with each other. The instant coffee consumer will see little value in an instant costing five times the price of the industry standard, and the gourmets themselves will not lower up to the romantically vacuous realms of instant – even if it did taste any good.

Coffee As A Commodity

Since the 1940s, there have been ongoing arrangements between producing countries (many of which rely on coffee as the chief export) and consuming countries that have aimed to stabilize production quotas to limit overproduction and the economy-shattering price drops they can cause. The inter-American Coffee Agreement, first signed in 1940 and the International Coffee Agreement (ICA) of 1962, like so much of coffee’s history, have their roots in politics, born out of the concern that Latin-American countries may be tempted into extreme left or right wing political tendencies if their export values weren’t guaranteed. Today the ICA is managed by the International Coffee Organization (ICO) and now includes members from 42 producing countries, equating to about 97 percent of all the coffee grown in the world, according to the ICO website. In effect, the agreement means that each producing country has a production quota, and when the price per pound falls, the quota is reduced and the price, in theory, goes up. What is “C-price”?
It actually only refers to the price of coffee on the New York Exchange (NYSE), so it isn’t indicative of the price being paid everywhere (since only a small percentage of coffee passes through NYSE), but it does act as a reference point for other market. Up until the later part of the 20th century, the stark reality of poverty, exploitation, violence and political corruption that the coffee industry has aggravated, in many countries over the years had been quite well covered up. The ICA, which was renegotiated every five years, expired in 1989 after failing to agree on new export quotas, and parties failed to establish new terms quickly enough. What ensued was a ‘coffee crisis’ that saw the supply of coffee vastly outweigh the demand. This drove down the price of coffee to only $0.77/50 pence per pound as the market became saturated, which spelled bad news for millions of farmers across the world. The Fair Trade Certification, under its original name, ‘Max Havelaar’ – the hero of a 19th century Dutch novel that critiques in practices of the Dutch East India Company in Java – was launched in the Netherlands, and aimed to standardize pricing, no matter what the availability of coffee at the time. On the whole, Fair Trade has to be a good thing if, as it claims, it is giving more money to coffee producers. The critics of Fair Trade will argue that there is insufficient transparency in the process, traceability is poor and that the simple freezing or tracking of prices does little to encourage farmers to improve the quality of their coffee. The other two official certifications of note are Organic and Rainforest Alliance. An organic certification has no bearing on quality, though. A Rainforest Alliance certification is often (but both always) partnered with an organic certification, as it goes a step further, requiring certain agricultural practices that promote sustainability, safeguarding of the environment, as well as welfare standards for producing families and their communities.

Speciality Coffee

Speciality Coffee is a term that has been used since the mid-1970s to describe coffee of high quality and value that is in some way representive of its origin, variety or growing and processing practices. Speciality Coffee is also sometimes sold at auction in the country of its origin, where roasters and importers bid for specific ‘lots’. The price paid for speciality coffee varies according to the C-price and its country of origin, but also, of course, according to its quality. Some roasters have, in recent years, begun building relationships with growers and in some cases dealing directly with them, known as a ‘Direct Trade’ relationships. The obvious benefits of Direct Trade, are that the farmer gets a fair price, the roaster has improved traceability of his product, and in some cases the ability to work with the farm on improving future seasons’ crops.
‘Relationship Coffee’ is another term that is sometimes used by speciality roasters. It usually means that there is an ongoing dialogue between the roaster and the grower in an effort to improve coffee quality and traceability.

The Role of The Roaster

We all know that roasting the coffee beans is an essential stage on the road to a mug of coffee. But its necessity aside, this keenly observed and succinct process that gracefully traverses the line between science and art, is nothing short of meteoric in its lasting effect on the character of the coffee. Decisions made at the roasting stage (as with most things in coffee) are irreversible, and it is for the home brewer, perhaps the most important stage of the entire chain of events that takes us from farm to cup. To better illustrate this, let’s compare coffee to wine for a moment. In wine production, the winemaker manages most, if not all, of the quality control points of the product, from growing, harvesting, juicing and fermenting through to filtering and bottling. The quality of the way it is served, however, is secured only by the consumer pouring the liquid at the appropriate temperature and finishing it within a sensible period of time. Any of the key people in the formation could claim that their reputation is in the hands of the other key players as, in normal circumstances, their powers only stretch as far as who they buy their product from, what they do with it once they have it, and who they sell it to. But it is the roaster who plays the most obvious middleman role between the beginning and end, and it’s the roaster that we, the consumer, best associate with.

The Skill of The Roaster

Roasters will buy coffee based on a number of factors; flavor is, of course, one of the most important, and this will in part be a reflection of how and when the coffee was picked, processed, graded, packaged and imported, and how these factors balance with price. Sustainability and ethics also play a part these days, so questions arise about how much a farm is being paid per pound of coffee, how sustainable the agricultural methods of the farm or estate is, and how the growers are being paid, if the coffee is the product of a co-operative effort from numerous smaller growers.
Once the coffee is in hand, then it’s the skill of the roaster that shapes the final character of the coffee and connects the dots between origin, terroir and specific variety with those of brewing method and cup quality. But it’s important to remember that bad green coffee can be tamed, but not entirely saved, by the hands of a great roaster, just as a bad roaster can very easily corrupt even the finest speciality beans. Mastering the roast is an art form that can be likened to few others. The complex chemistry and physics of roasting coffee have been the subject of hundreds of books and research papers, as scientists attempt to identify the flavorful and aromatic constitutes of good roasted coffee, and work out where they came from. Today, our understanding of roasted coffee is better than it has ever been, but the growing realization that coffee is enormously complex has only really cemented a feeling of acceptance as to how powerless we are to truly affect and select its attributes on a molecular scale. Part of coffee’s beauty is its ambiguity; it’s not roasted to an exact recipe of aldehydes, acids, sugars, carbonyls, caramels, caroenoids and other aromatic molecules in a perfect digital formula of saturation, contrast and brightness. Roasters are more like impressionist painters, where the artistry may be vague, imbalanced and imprecise, but the resulting composition as a whole can depict a richer, more emotional story through its imperfections.

The Evolution of The Coffee Roaster

The modern coffee roaster represents over 500 years of acquired knowledge. Improvements in design only became necessary once it had been established what was wrong with the equipment available at the time. A better design meant a better product, which would command a higher price for both the machine and the coffee it produced. Looking through the evolution of the roaster, there are three fundamental issues that the inventors have fought with. First is the even distribution of heat through the coffee bean mass, which we know gives a consistent and better quality roast. Second is the speeding up of the process of loading and unloading the roaster, which increases throughput and decreases labor cost. Third is the ability to monitor the roast by way of visual, or physical access to the coffee beans, which results in clearer precision and ultimately a better product.

Early Roasting

We will probably never know exactly when the first coffee roasters came into existence, since they almost certainly evolved organically from the regular cooking equipment of the day. Stone bowls and clay cups were certainly popular options, left to sit over hot coals or an open fire, and occasionally stirred to ensure even bean browning. The first known dedicated coffee roaster made an appearance in Persia in the early 1400s. This roasting plate was like a large perforated spoon, designed to sit above an open fire pit or brazier and roast small quantities of coffee at a time. The concave nature of the early roasting spoons also points to a general understanding of the importance of movement during roasting, to better aid even cooking. Cylindrical coffee roasters were the first major breakthrough. They came about in the mid 17-th century and were probably of Turkish origin. Mounted over an open fire and generally constructed from tin plate or tin-coated copper, these roasters were sealed units, turned by hand, in efforts to keep the beans moving and, they believed keep the aroma well contained. By 1660, these cylinder roasters were popping up in London, one example being Elford’s white iron machine, which was ‘turned on a spit by a jack’ and considered a huge technological leap forward, since the use of human labor was no longer required. It was perhaps the Dutch who took the most serious approach to coffee roasting equipment, as attested by humphrey Broadbent, ‘the London coffee man’ in 1722: ” I hold it best to roast coffee berries in an iron vessel full of little holes, keeping them continually turning, and sometimes shaking them that they do not burn, and when they are taken out of the vessel, spread ’em on some tin or iron plate ’till the vehemence of the heat is vanished.” This type of roaster subsequently evolved to become a free-standing contraption of larger proportions, also sporting a metal hood to help heat retention, more commonly used by coffee shops.

The Emergence of Commercial Roasting

Much of the coffee roasting that was taking place in Europe at the time was in the family home, in part because it wasn’t considered a skilled practice, and partly because it was an assurance of authenticity. Also, up until the end of the 18th century, roasters had pretty much all been small-scale pieces of kit, capable of processing no more than a few kilos of beans at a time.
Home roasting was a slow means to an end, though, sometimes taking up to an hour, which yielded coffee that had a baked character, lacking in acidity and bite. But this was the era of innovation across all industries, from dairy farming and distilling to textiles and paper-making, with new technology successfully cutting back the required workforce and improving quality and throughput. Coffee roasting was no exception. The tentative first steps came in 1824, when Richard Evans patented the first large-scale commercial coffee roaster. Besides its size, the cylindrical roaster had a
few added benefits over anything that had come before, including the facility to easily up-end the entire roaster to remove the beans from the roasting chamber. In the mid-19th century, quick unloading and reloading was an ongoing challenge that many inventors sought to provide a solution for, along with design modifications intended to help the roaster determine when the coffee was ready. Dating back to 1846, Dausse designed a roaster on the principle that coffee loses around 15-20 percent of its weight during roasting. Beans were weighed before loading, than a target weight, relative to the desired degree of roast and the country of origin of the beans, was calculated. But as consumers placed greater faith in the convenience of ‘pre-roasted’ coffee, bigger roasters were needed, and who better to supersize a roaster than America? James W. Carter of Boston patented the design for his pull-out roaster in 1846, a system that became the commercial roaster of choice for the following two decades. The Carter roaster was basically a manually turned sheet-iron drum, about the size of large wine barrel, that was fixed into a brink coal furnace. It had one major difference, though: loading and unloading of the coffee was performed by ejecting the whole drum from the furnace and opening a door on the side. Entire banks (or batteries) of Carter roasters were installed in the largest coffee companies of the time – such as the Dwinell-Wright Company of Boston.

Types of Heat Roasters

Almost all coffee roasters cook beans through a combination of different types of heat transfer: conduction, convection and radiation. Heating by conduction is very simple to understand. It is a transfer of energy that takes place when a hot, solid object makes contact with a cooler solid object: for example, when you pick up a cup of hot coffee and your hand warms up. The same thing happens during the roasting of coffee beans when cool beans touch the hot surface of the roaster, and also when a slightly hotter bean touches a slightly cooler bean.
Convection occurs where a liquid or gaseous heat source – in the case of a coffee roaster this is the air – moves as a continuous current, rapidly transferring energy as it goas. A convection (or fan) oven works in this way, which is why it cooks faster even at lower temperatures than a traditional gas oven. Heat transfer by convection is the preferred method of cooking for coffee roasters, because it requires lower temperature and less energy, yet rather conveniently, convection is also quicker. But when all is said and done, coffee beans cook mostly by the conduction, since once convective heat, rapidly permeates the outer layer of the coffee, it can then only transfer through the static structure of the bean through conduction from one solid layer to another. Convection speeds up this process

The Importance of Roast Date and Storage

Freshly roasted coffee doesn’t taste nice. By the way we are not talking about coffee freshly bought from the store, but coffee fresh off the cooling tray. After all, the coffee has just undergone a wholly unnatural experience; moisture stores and solid matter have been vaporized; sugars and acids have splintered into a diverse mixture of newly formed chemicals; caramelization and browning reactions have ensued, and the overall structure of the bean has been dramatically transformed, resulting in a near doubling of size and changes to porosity, color, density and weight. The coffee must be allowed to rest before it is ready to be turned into a tasty beverage. The most important element of resting is the process of ‘outgassing’, or the process of releasing carbon dioxide from the bean. Secondary to that are the minor chemical changes that also take place minutes, hours and even days following the roast. Freshly roasted coffee is approximately two per cent carbon dioxide by weight, and if left in a non-pressurized environment, it will release this gas more slowly as time goes on. This is all down to the internal pressure of the bean which – like an inflated balloon – forces carbon dioxide and other gases outwardly after roasting. Now, carbon dioxide is flavorless by itself, but when mixed with water – in, say, a French press – the hot liquid acts an effective solvent for the carbon dioxide, which quickly dissolves in and subsequently, out, of the water, creating lots of bubbles. The effect is like pouring a glass of fizzy cola over a sherbet, and as fun as that may sound, it doesn’t make for a great tasting cup. It has also been suggested that carbon dioxide is bad for brewing due to distribution it causes to the mechanics of brewing, where wet coffee grounds that are rapidly releasing carbon dioxide have the effect of propelling brewing water away from the flavorful solubles that rest within the hallowed inner walls of the coffee cell structure. One of the main problems, is that when carbon dioxide and water mix they produce carbonic acid. The subtle ‘tang’ that you experience from a glass of soda that has been left to go flat is the taste of carbonic acid. The point is that carbonic acid isn’t very delicious, it leaves a ‘licked-battery’ kind of sensation on the tongue, and it can become quite apparent in very fresh brews. The amount of time that coffee must be allowed to rest and outgas will depend on the approach to roasting and storage. Broadly speaking, darker and hotter roasts will have a higher internal pressure, so will they will outgas slightly quicker and more completely. Lighter and cooler roasts will do the opposite. Faster outgassing points towards a more porous bean structure, which is also more likely to go stale quickly. It would seem that a direct correlation can be made between the rate and extent of outgassing and the volatilization (departure) of aromatic compounds in the first week or so after roasting. A coffee’s aroma tends to be more noticeable in lighter roasts; in darker roasts, the destruction of volatile aromatics (or at least the good ones) eventually outpaces the formation.[/vc_column_text][/vc_column][/vc_row]