Coffee Processing

Methods of Processing Coffee

Coffee processing is generally divided into two types of processing: wet processing (wet method processing; the washed method) and dry processing (unwashed; the natural method), though in recent years new processing methods (e.g., semi-washed method) have been gaining favor.

Wet Processing Coffee

Wet method processing involves washing the coffee beans to remove the fruit from the beans along with any impurities. Wet processing of coffee occurs in several stages that include pulping, fermentation, drying, and milling.

During wet processing, the coffee’s parchment is removed by first removing the pulp in the process called pulping (or de-pulping).

Pulping Coffee

Pulping is usually done within 24 hours of harvesting the coffee cherry (fruit), and involves removing the outer flesh of the coffee cherry (the red skin and the mucilaginous pulp). This is usually done with a machine known as a pulper which uses rough rollers to loosen and break up the outer part of the cherry.

Demucilaging, Drying, and Hulling the Coffee

Next the coffee cherry’s mucilage is removed through fermentation by placing the cherry in a fermentation tank for 12 to 24 hours.

The coffee beans are then dried using either forced-air drying or spread out onto decks or patios (see hoshidana) to dry naturally in the sunlight (see sun-drying). When the drying is completed, the moisture content of the coffee beans is typically about 10.5%.

Hulling/husking is done with a machine called a huller, which mills off the parchment and the silverskin, and also polishes the beans, which at this stage are known as green coffee beans (milled but not yet roasted).

Dry Processing Coffee

Dry processing involves drying the coffee cherry (the fruits of the coffee tree) in the sunlight (or in a mechanical dryer) until the moisture content is about 10.5% while repeatedly raking and turning the coffee beans to separate them from any dried fruit remnants. The resulting product is known as parchment (pergamino; perghamino).

A benefit of the dry processing method is that the brewed coffee will tend to have more body than wet-processed coffee due to the fruit remnants left in with the coffee beans.

However, the acidity level of dry-processed coffee will generally not be as desirable as that found in a wet-processed coffee, which typically has a clean taste and bright acidity.

Pulped Natural Coffee Processing

Often used in Brazil where strip-picking is the norm, the pulped natural method of coffee processing involves first pulping the coffee to remove the silverskin – though this is done without the fermentation stage – and then sun-drying the parchment with much of the mucilage still attached, on a raised drying bed or on a patio.

The pulped natural coffee processing method works best in regions where the humidity is low so the coffee’s mucilage can be dried quickly without fermentation occurring.

The pulped natural method exhibits characteristics of both wet processing method (good acidity) coffees and dry processed coffees (sweetness, body), with some of the full taste of dry processed coffee yet cleaner in the cup, similar to a wet processed coffee.

Aquapulp Coffee Processing

Aquapulp is the process of removing the freshly-picked coffee cherry’s sticky pulp, or mucilage, through mechanical demucilaging, which utilizes machines to scrub the cherry.

The aquapulp process has gradually been replacing the traditional wet processing methods of removing the mucilage through fermentation and washing.

After the parchment is removed the coffee beans are sorted and graded based on local standards which vary in different regions. In general the beans are sorted into quality grades based upon size, shape, and other factors. (Also see Grading Coffee Beans.)

Grading Coffee – Removing Defective Coffee Beans

Screens with graduated hole sizing helps complete the grading process. Vibrating air tables are also used, employing gravity to separate the beans by density and to isolate defective (e.g., hollow or nicked) coffee beans, which can harm the taste of the final product.

Green Coffee Beans With or Without Silverskin

Some coffee processors who sell whole green coffee beans leave the silverskin on the bean since it serves as a protective barrier and then crumbles off naturally as chaff during the coffee roasting process. Other coffee processors polish off the silverskin.

Bagging the Coffee Beans for the World Market

Once the coffee beans are processed they are usually bagged in 100-pound coffee sacks and sold on the world market as green coffee beans (milled, but not yet roasted).

Roasting the Coffee Beans – The Art of the Roastmaster

The final step in preparing coffee for consumption is roasting, which involves heating/cooking/drying coffee beans in a coffee roaster in order to transform the physical and chemical properties of the green coffee beans so the desired flavors and aromas of the final cup of brewed coffee can be achieved.

Coffee roasting eliminates most of the moisture in the coffee beans and begins a series of chemical reactions known as pyrolisis. These chemical reactions change the chemical composition of the coffee beans and develop the coffee compounds associated with the flavors and aromas of the brewed coffee.

Bringing Out the Fine Flavors of the Beans

The goal of the skilled roastmaster is to apply the proper roasting temperature for just the right amount of time to bring out the best flavors of the particular coffee beans being roasted.

Roastmasters pay close attention to the color level of the roasting coffee beans as they expand and their hue changes. The color of the roasting coffee beans ranges from very light to very dark, and as the coffee beans lose moisture their density also changes.

Coffee roasting, in various aspects and instances, creates, modifies, and/or stabilizes the fragrance of the coffee beans as well as the body, taste, sweetness/bitterness, acidity, and aroma of the brewed coffee.

Coffee Roasting Machines

Roasting coffee requires skill as well as a proper coffee roaster. Many common roasting machines are heated with propane gas, using electricity to drive a drum. Roasting temperatures range from 370 degrees Fahrenheit to 540 degrees Fahrenheit (188 degrees Celsius to 282 degrees Celsius).

Roasting times vary from about 12 to 30 minutes, and the beans shrink about 20% by weight as they gain a dark hue and fragrant aroma. 25 of green coffee beans typically take about 15 minutes to roast, and 8 pounds of coffee cherry will make about 1 pound of roasted coffee (100 pounds of coffee cherry equals approximately 12 pounds of roasted coffee).

Fluid Bed Roasters

A Fluid Bed Roaster is a type of coffee roaster that agitates and roasts the green coffee beans using a column of hot air. The Fluid Bed Roaster, also called a Sivetz Roaster after Michael Sivetz who invented it, operates much the same as a popcorn popper.

Determining Coffee Roasting Time

Total coffee roasting time varies depending upon several factors including the quality of the coffee beans, their moisture content, and the grade of the coffee beans. Also affecting roasting time is the age of the coffee beans as well as the weather conditions where the coffee roasting is being done.

A primary factor in determining coffee roasting time is the type of roast required, ranging from Light Roast to Medium Roast to Medium-Dark Roast to Dark Roast.

Subtleties of the Coffee Roasting Process

The skilled roastmaster pays attention to the roasting time and temperature as well as more subtle considerations such as the appearance and fragrance of the coffee beans during roasting.

The roastmaster listens for the popping or cracking sounds of the roasting coffee beans – these distinct “cracks” occur at particular times during roasting. (See Roasting Coffee.)

Grinding and Brewing the Roasted Coffee Beans

Once the coffee beans are roasted they are reading for grinding and then brewing.

Coffee and Espresso Brewing Tips

For tips on brewing the perfect cup of specialty coffee see the Espresso Coffee Guide’s section on Coffee Brewing. For detailed definitions of coffee terminology see the Coffee and Espresso Glossary. You can also read detailed specialty coffee flavor profiles see Gourmet Coffees and Espresso Drink Recipes.

For step-by-step instructions on how to make a whole variety of exquisite espresso drinks see Pulling A Perfect Espresso Shot as well as Barista Guide to Perfect Lattes and Cappuccinos.

Also check out the history of coffee and espresso recounted in detail in our World’s Best History of Coffee.