Coffee Characteristics: What Affects The Quality of Coffee Before You Brew It
Coffee seems deceptively simple to prepare. Simply soak ground coffee beans in hot water and, voilà, you have coffee – or something that approximates it. However, coffee is remarkably delicate and finicky, both as a plant and as a beverage. Coffee from the same farm can taste dramatically different from one year to the next, and coffees harvested the same year from two nearby farms can have very different qualities. When you consider the many ways coffee can go wrong during growing, harvesting, processing and shipping, it’s even more amazing when you find a cup that makes you sit up and take notice. Here we’ll cover a few of the variables that affect the flavor and quality of your coffee before it reaches your brewer.
Species and Cultivar
There are dozens of species under the genus name Coffea, but only three of them that are routinely grown for the purposes of making our favorite beverage, coffee: Arabica, Robusta and Liberica. Nearly all coffee available from specialty roasters is Arabica, though some add high-quality Robusta beans to certain espresso blends. Dozens of cultivars (cultivated varieties) exist within the Arabica species, and each has its own qualities and characteristics. While soil, climate and other factors influence the manifestation of those inherent qualities, the cultivar determines what will be possible in the cup with a given coffee.
Soil provides many of the minerals and nutrients that the coffee plant absorbs, and these in turn affect flavor, body and acidity. Bourbon coffee grown in Kenya’s volcanic soil, for example, is very different from the same coffee grown in the limestone and clay-rich soils of Guatemala’s Cobán growing region, but has a great deal in common with Bourbon grown in Guatemala’s Antigua region, where the soil is similar to Kenya’s.
Coffee plants demand the perfect balance of sunlight, rain and temperature to produce the highest-quality beans. The particular climate of a region controls the length of the growing season as well as whether the trees flower, set fruit and ripen at the optimal times. Even small variations in temperature and rainfall can make a big difference in the quality of the harvest—a reality that has become more evident as coffee importers increasingly source coffee from specific regions and farms rather than from coffee mills, which often combine beans from numerous areas into larger lots and thereby obscure the distinctive flavors that differentiate one coffee from another.
Shade-grown coffee is growing in popularity for a number of reasons, not the least of which is that it tastes better than coffee grown in full sun. Cloudy skies, forest canopy and tall mountains all provide shade that protects coffee plants from the harsh heat of the sun, which can burn leaves. The cooler temperatures allow the cherries to ripen more slowly, developing fuller flavor. Meanwhile, the diversity of plants in the shade canopy encourages a similarly diverse population of birds and insects, many of which protect coffee plants from pests that can damage the crops, encouraging a higher, better-quality yield.
The best coffees almost invariably come from regions where coffee farmers have implemented farming practices and techniques that coax the best flavors from the bean. Proper fertilization, irrigation, pruning and care encourage the development of high-quality coffee.
Coffee trees get old and tired, so it’s important for farmers to replenish their trees continuously. A tree doesn’t produce coffee cherries until it is 4 years old and can’t be harvested for another year. It is at its most productive–and yields the best coffee–between years 7 and 20. Farms that do a good job of tree management are rewarded with better harvests and higher-quality beans.
Coffee cherries reach peak ripeness at different times. Mechanical harvesters have no way to differentiate between ripe and unripe coffee cherries; they simply strip the trees of cherries and dump them all, ripe and unripe, into a big batch. Plantations that harvest by hand instead can pick and choose, only harvesting cherries that are perfectly ripe for the best flavor. Once coffee cherries are harvested, they must be processed immediately to avoid mold or rotting.
There are three main ways of processing coffee cherries, and each contributes very different qualities to the finished coffee.
Dry (or natural) processing is the more traditional method, and is often used by smaller farms in rural areas. The coffee cherries are spread out to dry on rooftops or platforms in the sun for seven to ten days. During the drying phase, the cherries must be raked and turned regularly to prevent the development of mold, which would contribute “off” flavors. Once the skin and fruit have become brittle, they are removed from the bean, usually by hand. Dry-processed coffees tend to have fuller body, thicker viscosity and more restrained acidity than wet-processed, or washed, coffees, and are more likely to taste earthy. They are also far more likely to exhibit wild, rich fruit flavors that are seldom found in washed coffees.
Wet-processed (or washed) coffee is more common in areas where water is plentiful. Coffee cherries are placed in vats of water to soften, usually overnight, then run through a machine that removes most of the fruit from the seeds. The pulped beans are allowed to ferment in water vats to make it easier to mechanically remove any remaining fruit and mucilage before they are dried, either naturally or in a mechanical dryer. Wet-processed coffees generally have a cleaner profile with brighter acidity and light to medium body. If they’re not handled carefully, though, there’s a greater chance of mold developing on the beans while they are drying or, conversely, a risk of drying the beans too quickly. Both of these can lead to unsavory tastes in the cup.
Pulp natural (or semi-washed/honey-prep) processing is a hybrid method used in some regions. With pulp natural, the coffee cherries go through the first step of the washing process to remove the outer skin, but are allowed to dry with the fruit pulp clinging to the parchment layer covering the bean instead of immediately undergoing fermentation and washing . Pulp natural coffees tend to taste cleaner than dry-processed coffees but are perceived to have more body and muted acidity than fully washed coffees. They frequently exhibit sweetness, especially honey, brown sugar and caramel flavors, and a level of fruitiness that falls between that of wet- and dry-processed coffees.
For more details on coffee processing, including variations on the above three methods, please check out our “farm to table” article.
Coffee is sorted at several stages between harvesting and shipping, and each sort can improve the quality of the finished product. The coffee cherries are sorted immediately after harvest to remove unripe, misshapen or otherwise substandard berries. During wet processing, beans that float are removed and discarded, adding a second layer of sorting. Regardless of the processing method used, beans may be sorted again for size, shape and color before milling and packaging. Each sort removes coffee beans that don’t meet particular standards, leaving only the highest-quality beans to make it into your cup.
While green coffee beans don’t stale as quickly as roasted coffee beans, they will lose flavor over time. The way they are stored before, during and after shipping can significantly affect cup quality. Traditional shipping in burlap bags, for example, exposes coffee beans to moisture, air and the odors of any products or substances nearby. For this reason, many importers prefer coffee shipped in alternative containers, such as multi-layer plastic GrainPro bags, which protect the beans from moisture, odors and other outside factors that can affect the flavor.
Coffee stored in a warehouse for months or, in some cases, a year or more, will not be as flavorful as coffee that is fresh from harvest. It’s still difficult for consumers to know when their coffee was harvested, but many roasters and green coffee bean suppliers are getting much more particular about and forthcoming with this information. Direct Trade, Fair Trade and events like the annual Cup of Excellence auctions make it easier to keep track of when and where coffees were harvested by rewarding growers of quality coffees with higher prices and encouraging greater transparency in coffee sourcing.
Roasting affects coffee flavor profoundly. Heat causes chemical changes within the coffee bean, caramelizing the sugars and bringing out the flavors of the acids and other elements present. The same coffee will taste completely different at a light roast level than it does at a medium or dark roast level. In fact, roast makes such a difference that there are entire books devoted to proper roasting techniques, and many coffee roasters closely guard the precise roasting profiles for the beans they sell.
Once coffee is roasted, its flavor changes dramatically and rapidly. Most coffees reach peak flavor between 4 and 7 days after roasting, though this varies somewhat from bean to bean and there is disagreement over the details. All specialty roasters whose coffee we carry print the roast date on the coffee they sell so that consumers themselves can judge freshness.
For more information on keeping coffee fresh at home, see our guidelines for coffee storage. In addition, we feature brewing guides for you to enjoy and give feedback on.
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