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Green-Coffee Processing and Storage
This chapter was cowritten by Ryan Brown.
Green-coffee processing affects cup quality as well as how one should roast beans. Once a bean has been processed, a roaster must carefully control its packaging and storage conditions to prevent degradation of quality before it’s roasted.
Primary Processing Methods
Washed, natural, and pulped natural are the three primary processing methods of specialty coffee.
Wet/Washed
The Washed, or wet, process consists of the following steps:
1. Pulping of the cherry to remove the skin.
2. Removal of the sticky mucilage layer by fermentation or mechanical means. 3. Washing of the beans to remove loosened mucilage. 4. Drying of the beans in parchment, either mechanically for 1-2 days or in the sun for 3-16 days.
Dry/Natural
The natural, or dry, process consists of partially or completely drying the coffee cherries on the tree and then husking the cherries to remove their skins. Alternatively, the cherries are picked when ripe and then dried before husking.
Pulped/Natural
In the pulped/natural process, the cherries are pulped to remove their skin and set to dry with the mucilage layer intact. This method delivers a sweeter, cleaner cup than does the traditional natural process.
Washed processing produces cleaner, more acidic, more consistent, and generally more-prized coffee than natural processing does. Washed coffees also tend to be denser and require more aggressive roasting. The dry process can take several weeks and yields coffee with less acidity, more body, and earthier flavors than washed coffee. Arid growing areas often use the natural process because it requires much less water than the washed process. Natural-processed coffees burn more easily during roasting, so one should use lower charge temperatures and gas settings when roasting those beans.
Green Coffee Storage Until recent years, all coffee was packaged in burlap (jute) sacks and shipped in containers, arriving at roasters months after the coffee was processed. Roasters and importers frequently had the experience of cupping a coffee at origin, and perhaps cupping and approving a “pre-shipment sample,” only to receive coffee ruined by exposure to poor atmospheric conditions in storage or in transit.
In the past ten years, several small, quality-driven roasters have spearheaded a revolution in green-coffee packaging and transport. Many roasting companies, even some of the smallest ones, now buy coffee directly from farmers, share cupping and green-grading information with the farmers, and demand speedy delivery of coffee in packaging designed to preserve its freshness and quality. Such packaging is costly but justified, given the ever-increasing premiums paid for specialty coffees.
The following is a survey of the more prominent packaging options:
Burlap (jute) bags are the most common and economical option for packaging and transporting greencoffee. Jute is a renewable resource, and the bags are cheap; their use requires no special skills or equipment beyond those that are standard at any dry mill or exporting operation. Burlap sacks do not protect coffee from moisture or odors, however, so the coffee is vulnerable to damage during transport and storage.
Burlap bags are the most economical option for packaging and transporting green coffee.
Both vacuum-sealed bags (left photo) and GrainPro bags (right photo) protect beans from moisture and odors.
Vacuum sealing is the best available packaging for green coffee. Vacuum-sealed bags protect beansfrom moisture, odors, and oxygen, dramatically slowing the respiration, and therefore the aging, of green coffee. Before vacuum sealing, care must be taken to measure beans’ water activity to prevent development of mold during storage. Vacuum packaging costs approximately USD 0.15-0.25 per pound (EUR 0.45-0.75 per kilogram), requires special equipment and skill to implement, and often delays shipment of green coffee, so it is not without its costs and risks.
GrainPro and other hermetically sealed bags protect coffee against moisture and odors and arecheaper and easier to use than vacuum packaging. GrainPro bags preserve coffee significantly longer than burlap sacks but perhaps half as long as vac-sealed bags do. At a cost of about USD 0.05-0.10 per pound (EUR 0.15-0.30 per kilogram), GrainPro bags are often the best and most practical option for quality-conscious roasters. As with vacuum sealing, to prevent development of mold and other microorganisms during storage, it is important to measure beans’ water activity before packaging them in GrainPro bags.
Freezing —that is, storing green coffee in vacuum-sealed bags at a temperature below 32°F (0°C)—preserves flavor almost perfectly for years. Some roasters freeze special lots of beans and offer them as “vintage” coffees years after harvest, but there is not much consumer demand for such coffees at the moment. While it’s impressive to experience five-year-old beans that taste as good as last month’s crop, freezing is expensive and, arguably, wasteful. Freezing is an alternative worth considering in hot climates, however, as storage in extreme heat for a few days will ruin most green coffees.
Regardless of the packaging type she chooses, a roaster should take steps to ensure that her warehouse provides stable storage conditions all year round. Excessively warm or humid conditions; storing beans high off the ground, where the temperature may be hotter than realized; and storing beans too close to a hot roasting machine can all degrade green-coffee quality.
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