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Coffee from Farm to Table

August 29, 2013

The journey of coffee from plant to beverage is a long one fraught with peril at every stage. Before they reach you, coffee beans must be planted, harvested, processed, dried and milled, rested, roasted and packaged for shipping to you. At every one of these stages, minor differences, errors and variations can introduce faults – or conversely, contribute benefits – to the flavor, aroma, body and acidity that will show up in the finished cup. Even after the beans reach your doorstep, the grind-and-brew method you choose can affect the quality and flavor of your coffee. For more on how taste is affected prior to purchase by the consumer, please see our “coffee characteristics” article; here we’ll focus more on what happens when all along the way to your table. 







First Things First





The coffee bean is actually the seed of the coffee tree, which grows small fruits commonly referred to as cherries. The seeds generally grow in pairs inside the cherry, but 5 to 10% of the cherries harvested will have a single round coffee bean instead of a pair of flattened beans. Those beans, called peaberries, are removed during sorting. In some cases, they are discarded, but in many regions peaberry coffee is considered richer and more flavorful and is sold separately for a higher price.





Coffee beans are surrounded by five protective layers, most of which will be removed before the coffee is ready to ship. The skin, also called the pericarp or exocarp, surrounds the entire package. Directly beneath the skin is the pulp, or mesocarp. Inside the fruit pulp is a layer of pectin, the sticky mucilage, which surrounds the parchment. The parchment encloses the coffee bean, which is coated with silver skin, a fine, thin skin similar to a peanut skin. All of these layers will be removed by processing before the coffee ships. But before we talk about processing, there are a few other important parts of the coffee journey to understand.







Growing





From choosing the right coffee varieties to deliberating over irrigation methods and crop management, coffee growers make hundreds of small decisions that affect the quality of the coffee they grow. The farmer must decide which coffees to grow, where to plant them, how to fertilize them and when to water them. Every coffee variety offers benefits and drawbacks for the farmer, and each will flourish under differing conditions. Fertilization, shade cover and proper irrigation all affect the flavor and yield of the coffee crop.





Most trees on plantations are grown from propagated seedlings. The coffee tree won’t set fruit for at least four years, and may not produce a reliable yield of coffee cherries until it is closer to seven years old.





A mature coffee tree will flower about eight days after the first big rain following the last coffee harvest, with hundreds of the delicate white blossoms covering the branches of all the trees on the plantation. Each blossom will last just about 12 hours. Rain during those twelve hours can interfere with fertilization. Insufficient moisture can cause the flowers to wither and drop off the tree before they open.





If everything goes right, though, and an obliging butterfly, bee or stray breeze drops pollen on the bloom, the fertilized flower will wither. Six to eight weeks later, a tiny fruit will develop there. In another six weeks, the coffee trees will be covered with glossy green coffee cherries growing in clusters on the branches. The cherries will change color from green to red – or in some cases yellow or orange – between 30 and 35 weeks after the initial flowering.





A single coffee tree will generally produce 1 to 1½ pounds of roasted coffee beans annually. An Arabica tree will reliably produce harvests for 10 to 15 years. Because of the length of time required to bring coffee trees to production age, coffee farmers must continuously monitor and replace older trees with young trees to maintain a fruitful yield.





There are, however, many factors outside the control of the coffee farmer. An ill-timed hurricane can devastate an entire harvest. Rain at the wrong time can keep flowers from setting fruit, and a windstorm can sweep blossoms off the branches before they’re fertilized or have set fruit. An infestation of coffee borer or infection with coffee leaf rust may destroy a whole orchard and sweep away years of work. Over the past several years, extreme weather events and changing climate factors have affected the coffee harvest in nearly all of the coffee-growing regions of the world.







Picking/Harvesting





Coffee is harvested in one of two ways: strip picking and selective picking.





Strip-picked coffee is harvested all at once, either by hand or using a mechanical harvester. In lowland regions with fairly flat coffee orchards, plantation owners employ harvesting machines that make short work of picking coffee. On hilly land, the picking is done by hand, but pickers simply strip all the cherries from the branches without consideration for their degree of ripeness.





Unlike many fruits, coffee cherries don’t continue to ripen after they’re picked. Because of that, they should be picked at peak ripeness to ensure fully developed flavors in the coffee bean. In addition, on lowland plantations with rainy climates, flowering and fruiting continues throughout the year. In those regions, it’s not unusual to find ripe coffee cherries, unripe coffee cherries, open flowers and flower buds not just on the same tree, but even on the same branchlet. This makes it impossible to reliably harvest only ripe cherries by strip picking.





Selectively harvested coffee is always handled by experienced pickers who only choose cherries at peak ripeness. The process is far more time-consuming and labor-intensive but ensures that coffee is harvested at the optimal time; thus, it’s most commonly reserved for high-quality Arabica coffee. The harvesters make a pass searching for cherries at peak ripeness about every 8 to 10 days, and a good picker can harvest between 100 and 200 pounds of cherries a day. Those cherries will produce between 20 and 40 pounds of coffee.





At the end of the day, the coffee cherries are hand-sorted to remove any unripe fruit, leaves and branches. Sorted cherries are then either packaged for transport to a processing center or processed on the premises.







Processing





Cherries are processed as soon as possible after harvest to reduce the chance of spoilage. The method of processing generally depends upon the region and the resources available. Most coffee-growing regions use one processing method almost exclusively, but small farm holders are increasingly experimenting with different types of processing. Because processing style makes a distinct difference in terms of cup profile, many roasters now state it on their coffee labels.





Washed (Wet)



In areas with plentiful water, the cherries are most often processed using the wet method, and the resulting coffee beans are called “washed” coffee. Washed coffees typically have a clean cup profile with fine acidity and lighter body.





Washing consists of several steps. The cherries are dumped into a tank, which is then filled with water. The water carries the cherries through a trough with a grate at the bottom. The heavier cherries drop through the grate to the bottom of the trough. Unripe or damaged cherries, which are lighter, are carried away by the water and discarded. From there, the good cherries are carried through a de-pulping machine, which uses water to force them through a series of holes to remove the skin and pulp from the bean. The pulped cherries are agitated in the water to remove as much of the fruit pulp as possible. The pulp is carried off by the water and will eventually be dried to use as mulch.





The coffee seeds proceed to a fermentation tank, where they will be allowed to ferment for 24 to 48 hours, until the sticky mucilage dissolves. This process is closely monitored so that it can be stopped at precisely the right point. If the beans soak too long, the coffee will have an unpleasant, harsh, fermented taste.





At this point, the moisture content of the coffee beans is about 57%. Before processing can continue, that must be reduced to between 11% and 12.5%. The beans may be dried in the sun, in a mechanical dryer or using a combination of the two methods. Whichever method of drying is used, the final product is parchment coffee, beans stripped of their pulp.





Sun-drying



Workers spread the beans on flat concrete or brick patios in layers no deeper than 10 cm. For the next 8 to 10 days, workers will rake and turn the coffee beans several times a day to make sure that they dry evenly. On many farms, the patios have been replaced with raised or parabolic drying beds. Raised drying beds are waist-high tables with mesh floors that allow for better air circulation and faster drying. Parabolic drying beds are raised drying beds under a protective covering similar to a hoop house. They’re common in rainy climates.





Mechanical Drying



Hot-air drying machines dry the coffee beans in 12 to 24 hours. They’re typically used on larger plantations, where the patios or drying beds aren’t sufficient to effectively process the entire harvest at once. Mechanical drying reduces some of the risks associated with sun-drying but increases the risk of over-drying the beans.





The washed/wet processing method produces a cleaner cup profile with more pronounced acidity and light to medium body. Because it involves removing the fruit pulp before drying, the flavors that remain are more or less those that are intrinsic to the bean. Washed coffees, therefore, have a more predictable flavor profile than natural-processed coffees, which we turn to now.





Natural (Dry)



Natural processing is the most traditional method of coffee processing and is often used in countries and regions that have fewer resources.





Immediately after picking, workers sort and clean the cherries to remove dirt, twigs and leaves, as well as berries that are unripe, overripe or damaged. The cleaned, sorted cherries are spread in the sun to dry on patios or on raised, matted platforms. Depending on the climate and the weather, it can take up to four weeks for the cherries to dry to the point where the skin and fruit can be easily removed. During that time, workers rake or turn the cherries by hand to prevent the formation of mildew and to ensure that the fruit dries evenly.





On larger farms, particularly on farms in damp climates, the cherries may be dried in machines instead of in the sun. Machines reduce the drying time to days rather than weeks but increase the risk of over-drying the coffee cherries. Over-drying results in too many broken beans, while under-dried coffee is prone to attack by fungi and bacteria.





When the cherries have dried sufficiently, they are sent to the mill, where the outer layers of the cherry will be removed all at once by a hulling machine before the beans continue on to be milled, sorted and graded.





Natural-processed coffee is common in Ethiopia, Haiti, Brazil, India and Ecuador but is not confined to those countries. Drying the bean in the fruit produces a heavier body with lower acidity and contributes intense, exotic berry and fruit flavors. Because of this, many estates throughout the world are experimenting with methods of processing coffee in their attempts to produce superior coffee with distinctive flavors.





Semi-washed



Semi-washed coffees, also described as pulp natural and honey process, are processed using a combination of the wet and dry processing methods. The mature cherries go through the first step of the washing process, where the skin and fruit pulp are removed. At that point, instead of moving the beans to a fermenting tank to dissolve the mucilage, the beans are spread on drying tables or patios and allowed to dry with the mucilage still clinging to the bean. The natural sugars and alcohols in the mucilage will contribute to the flavor, sweetness and acidity in the cup.





Because this mucilage will damage mechanical dryers, semi-washed coffee must be dried in the sun on flat, even surfaces. The drying process is even more crucial in semi-washed coffee because any unevenness in the drying surface can cause the mucilage to condense on the bed and promote rot. Workers rake the beans frequently to ensure even drying and prevent fermentation. The remaining mucilage dries into the bean, changing the flavor profile considerably.





Semi-washed coffees are characterized by intense sweetness, rich mouth feel and rounded acidity.







Resting





After processing, the coffee bean should remain in parchment for 15-90 days, with the ideal time depending on many factors. This period is called resting, or reposa. The parchment helps protect the coffee bean from unwanted flavors and inconsistent moisture while the cell structure strengthens. Coffee that isn’t rested long enough before milling will age faster and can pick up off flavors during shipment and storage.





On the surface, resting seems relatively uncomplicated: store the processed coffee beans in a cool, dry, shaded area for a length of time. In practice, it can be far more complex. In hot, humid regions or in regions where the temperature and humidity fluctuate, it can be a challenge to maintain stable temperature and humidity levels. In addition, resting coffee needs good ventilation, and moving air contributes to temperature instability. Coffee that is subjected to such fluctuations tends to have a baggy or stale flavor.





The resources of the farm or washing station, the climate and the processing methods typical of the origin will all influence the ways that farmers balance ventilation, temperature and humidity control during this rest period.







Milling





Milling, sometimes referred to as dry milling to distinguish it from earlier parts of the process that remove the skin and fruit, includes a series of steps: parchment removal, then sorting and grading the coffee for quality.





Hulling



The first step in milling is to remove any remaining material from the bean, including the dried parchment alone, parchment and mucilage or the entire dried fruit. This may be done by putting the beans through a millstone, which will rub away the outer layers, or using more sophisticated machines that remove the outer layers in other ways.





Polishing



Some coffees may be put through a polishing machine after hulling to remove any remaining silver skin. This both improves the appearance of the green coffee beans and reduces the amount of chaff during roasting. Some experts believe that polishing raises the temperature of the coffee bean, which can cause changes in its chemical makeup and affects its flavor.





Cleaning and Sorting



From here, the coffee goes through a series of machines and processes that will sort the coffee by density and size while removing any debris that may have survived earlier processing stages. The sorting methods include gravity, sieving and vibration, to sort out the heaviest, densest and best beans. Finally, the beans are sorted by color. Most high-quality coffees are color-sorted by hand, with experienced workers picking out discolored and defective beans as they pass by on a conveyor belt. Specialty coffees may go through two or three rounds of color-picking to ensure high quality. There are machines that can do color-sorting using computerized parameters. The machines are expensive, however, and are not widely used in the specialty coffee industry.





Grading



Finally, the coffees are graded according to various criteria. The criteria vary from region to region, as does the consistency of their application. Possible grading criteria include bean size, the elevation at which the coffee was grown, how it was picked, how it was processed, the number of imperfections and the cup quality.







Aging





A few coffees are aged using various methods. The most notable of these are Sumatran and Indian Mysore coffees, which are often stored for 1 to 3 years under specific conditions meant to change the flavor profile of the resulting coffee. The best-known of these processes is monsooning, which is meant to duplicate the conditions experienced by 18th century coffees shipped by sea in burlap bags. Monsooned coffees are stored in burlap or jute bags in specially built warehouses that expose them to the winds and rains of the monsoon season. The process flattens the acidity and heightens the sweetness of the coffee, resulting in a cup profile with heavy body, low acidity and intense sweetness infused with earthy, musty or funky flavors that are highly prized by some coffee connoisseurs. Another method gaining popularity involves conditioning green coffees in wine, port or whiskey barrels for a period of time in order to impart flavors usually associated with dry processing. Monsooned coffees, and aged coffees in general, are generally recognized as an acquired taste.





 



Shipping





Conditions during shipping, even including the type of container in which a coffee is shipped, can affect flavor. Coffee beans are remarkably absorbent of other odors and flavors around them. Traditionally, coffee beans were shipped in burlap or jute bags, which allow odors and flavors to penetrate and infuse the beans. Over the past several years, many specialty coffee importers have started using bags lined with a gas-impermeable layer (e.g. GrainPro) to prevent this.





Due to cost considerations, most coffees are shipped by sea, which can take anywhere from two weeks to three months. Conscientious coffee roasters are starting to take the shipping time, along with resting time, into consideration when choosing specialty coffee.







Roasting





Roasting is the process that transforms hard, waxy green coffee beans into aromatic nuggets of concentrated coffee flavor. This is accomplished by subjecting the green beans to heat, which produces pyrolysis, resulting in chemical changes that release coffee oils and caramelize coffee sugars. Coffees are generally roasted in the importing countries rather than at origin because freshly roasted beans stale rapidly and, thus, must reach the consumer as quickly as possible.





The roasting process can be summarized in a single sentence: heat green coffee beans evenly until their color changes from green to the desired shade of brown. In practice, though, there are so many variables that even expert roastmasters aren’t assured of getting it right. The many factors that affect a coffee roast include bean variety, origin, moisture content, ambient temperature, ambient humidity, age of the bean, roasting temperature, roasting time and profile (temperature plotted against time)–and those are only the most obvious. Artisanal coffee roasters take all of these factors into account and more when roasting a new coffee, and will often work with it repeatedly until they create a roast profile that most consistently draws out the best flavors from that particular coffee bean.





After the coffee is roasted, the beans must be cooled rapidly to stop the roasting process, and then the beans rest for a period of time that varies from a few hours to a day. During this time, the beans release carbon dioxide, a process called outgassing. The largest degree of outgassing takes place within the first few hours. During that time, oxygen won’t damage the coffee. After that, the flavor of the coffee begins to decay as oxygen robs the bean of volatile elements that contribute to taste. Packaging the roasted coffee beans in bags with one-way valves allows the beans to continue to outgas safely in a mostly oxygen-free environment.





While coffee roasters must concern themselves with all of the variables discussed above, consumers are generally most interested in the roast date and roast level, i.e. how darkly the coffee is roasted.





About roast date, most coffees reach optimal flavor between 4 and 7 days post-roast. Beyond that time, the flavor begins to deteriorate unless it is stored in a way that retards staling. See our information on home storage of roasted coffee for more details.





Each roast level has particular flavor characteristics, and each coffee exhibits different flavors at different roast levels. Most experienced coffee drinkers know what to expect from coffee roasted to various levels; for a primer, see our article on the subject.







Grinding





Going from perfectly roasted bean to flavorful coffee requires an intermediary step: grinding the beans. The relative coarseness and evenness of the grind makes a profound difference in the quality of the finished cup. In addition, each brewing method has a sweet spot for a particular grind, and some coffees require more grind-related fine-tuning than others for best results. There are a number of ways to get your grind on.





Buy Ground Coffee from the Roaster



Most coffee roasters sell their coffee either as whole bean or ground to order. Many offer at least two grind levels: drip grind or espresso grind. Choose ground coffee based on your method of brewing.





In general, this is the least preferred method of obtaining ground coffee, which goes stale much more quickly than whole-bean coffee. People who are particularly sensitive can taste the difference in coffee ground immediately before brewing and coffee made from grounds that sat just half an hour before brewing. Among the very best investments you can make to improve the quality of your coffee is a high-quality coffee grinder.





Blade Grinder



Many manufacturers market blade grinders as coffee grinders. In reality, these are choppers, not grinders. They break the beans up into smaller pieces, but don’t offer you much control over the process at all. There’s no way to achieve a truly even grind with a chopper, and attempts to get finely ground coffee from one can heat the coffee, leading to flavor deterioration. While blade grinders are an inexpensive way to pulverize coffee beans, nearly every coffee aficionado recommends that you avoid them. These days, you’ll find a considerable assortment of burr grinders on the market for nearly every budget level.





Burr Grinder



Burr grinders are the preferred method of grinding coffee for home use. They work by crushing coffee beans between flat burrs (sometimes referred to as plates) or conical burrs, reducing them to an evenly ground pile of particles. Burr grinders allow you to set the desired coarseness for your grind. The more expensive grinders allow you to choose from among dozens of grind settings, giving you a high degree of control—something especially valuable for espresso extraction. The best of these even allow you to save grind profiles so that you can instantly reproduce the perfect grind for various coffees and coffee-making methods. See here to read more about coffee grinders and grinding coffee.







Brewing



The final step in the journey from farm to cup is brewing. At this point, with all of the quality controls exerted at each step along the journey, you’d think little could go wrong to spoil your cup. In fact, the brewing method you choose – and how well you use it – has a major effect on cup flavor and quality. There are literally dozens of coffee brewing methods, and it’s possible to produce excellent coffee from high-quality specialty coffees with any of them. As you experiment, though, you’ll find that different brewing methods produce strikingly different flavor profiles even when holding the coffee constant. Check out our coffee brewing section to learn more about the various methods of brewing coffee and experiment to find the profiles you most enjoy.








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