How Does Kenya's Coffee Grading System Relate to K72 Processing?

K72 is Kenya's 72-hour washed process: cherries are depulped, fermented for 24 hours, rinsed with clean river water, then soaked and fermented again for 24 hours and rinsed, repeated three times for 72 hours total. Kenya coffee is prized for bright, clean acidity, and lots such as Asalia and Sachini Estate PB show how the method shapes flavor.

The coffee grading system sorts beans by size and quality after processing, and K72 lots are typically graded before export and roasting. Varieties SL28 and SL34, grown at high altitude, contribute much of the flavor associated with Kenyan coffee. The article also shares roasting curves and brewing parameters for two Kenyan beans, from origin to cup.

In the landscape of specialty coffee, Kenyan coffee stands out with its bright, clean acidity and full-bodied flavors, and the K72 washed processing method is its signature craft. This circulating fermentation system, developed on the basis of traditional washing, completes processing through three rounds of soaking and rinsing, each lasting 24 hours, totaling 72 hours—hence the name K72. This article will systematically outline the specific operational steps of K72, analyze the flavor origins of Kenya's high-altitude producing regions and varieties such as SL28 and SL34, and introduce Kenya's coffee grading system. At the same time, the roasting curves, brewing parameters, and flavor performance of two Kenyan beans from Front Street Coffee—Asalia and Sachini Estate PB—will also be shared, providing coffee enthusiasts with a complete reference from origin to cup.

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As the specialty coffee market continues to expand, beyond natural and washed processing, more and more processing methods are entering coffee lovers' view. Among them, Kenya's K72, developed on the basis of traditional washing, is highly recognizable. In this article, Front Street Coffee will walk everyone through the complete process of Kenya's K72 processing method.

What is Kenya's K72 washed processing method?

As Front Street Coffee mentioned above, this method was born from traditional washing techniques and improved upon them. Kenyans first adopted the idea of fermenting, then washing, and repeating the cycle: on the day of harvest, post-processing begins immediately. The highest-quality coffee cherries are selected first, depulped, then fermented for 24 hours, and rinsed with clean river water. Then they are soaked and fermented again in clean water for 24 hours, rinsed again, and this cycle is repeated three times, totaling 72 hours. Thus it became known as the Kenyan-style 72-hour fermentation washed processing method, or K72 for short.

K72 fermentation washed processing method flow:

① First washing and fermentation After the coffee cherries are harvested, they are first selected by water flotation based on density. The principle lies in the differences in density and mass of the coffee fruit itself: dense, heavy beans sink to the bottom, while low-density ones float on the surface. Highly ripe, good-quality fruit has greater density and will be selected to enter the next step of processing.

After selecting high-quality, sufficiently ripe fruit, the skin is removed, and they undergo washing and soaking, allowing the residual pectin mucilage on the green bean surface to initiate fermentation. Pectin contains natural sugars and alcohol compounds, which play a key role in the development of coffee's sweetness, acidity, and overall flavor. This fermentation lasts 24 hours, after which 80% to 90% of the pectin can be removed, leaving only the flavor substances inside the bean.

② Second washing and fermentation Next comes the second round of washing and fermentation. The coffee beans cleaned in the previous step are soaked in water again for 24 to 48 hours. This process increases protein and amino acid content, and the coffee's acidity thereby presents complex and delicate layers. Finally, all remaining pectin is removed, and the coffee beans are transferred to raised drying beds for sun drying.

The fermentation lasts as long as 24 hours, and after fermentation 80–90% of the pectin can be removed, leaving only the flavors inside the coffee beans. Finally, all remaining pectin is removed, and the coffee beans are moved to raised drying beds for sun drying. The drying time depends on weather conditions, generally taking about 5–10 days to complete.

Front Street believes that coffee beans processed with Kenya's 72-hour fermentation washed method undergo long fermentation at low temperatures and are finally dried through dehydration before completion, which gives the beans a brighter, cleaner yet fuller flavor.

Kenya coffee growing conditions

Of course, the quality of a coffee bean cannot depend solely on whether the processing method is good or bad. More importantly, it depends on whether the coffee bean itself is strong enough. Front Street Coffee has also often said in previous articles that the flavor of a coffee bean depends on its coffee producing region, variety, and processing method. In other words, the quality of the processing method is built on the premise of high-quality coffee fruit.

Kenya is located in eastern Africa, with the equator crossing its center and the East African Rift Valley running north to south. It borders Somalia to the east, Tanzania to the south, Uganda to the west, Ethiopia and Sudan to the north, and the Indian Ocean to the southeast. The country has many plateaus, with an average altitude of 1,500 meters. Mount Kirinyaga (Mount Kenya) in the center has an altitude of 5,199 meters, with snow on its summit, and is the second-highest peak in Africa.

Kenya belongs to a tropical producing region, with two rainy seasons each year and two harvests: 60% concentrated from October to December, and the other 40% from June to August. Coffee is mainly grown in volcanic areas at altitudes of 1,600–2,100 meters around the capital Nairobi and the Kenyan mountains. This altitude is suitable for coffee beans to develop flavor because lower temperatures in mountainous areas slow growth, allowing the aromatic components of the coffee beans to fully develop, making the fruity acidity more pronounced and the texture harder. This fertile, crescent-shaped coffee zone is the main producing area for Kenya's specialty beans.

Front Street Coffee also often says that Arabica coffee beans must have altitude restrictions for their growing conditions. The higher the altitude, the better the flavor, and the richer its acidity. No wonder Kenyan coffee is famous for its excellent acidity.

But Kenya's acidity is completely different from that of neighboring Ethiopia's coffee. Coffee fans all know that Front Street Coffee's Ethiopia coffee beans are famous for their bright citrus-lemon acidity, while Front Street Kenya's acidity is more of a cherry tomato acidity, which brings us to its coffee variety flavors.

Kenyan coffee bean varieties

The main varieties grown in Kenya are SL-28, SL-34, Ruiru11, and Batian. According to Front Street Coffee's understanding, these varieties are all products researched by the Kenya Coffee Research Institute.

SL-28, SL-34

SL actually stands for Scott Labs, Scott Laboratories. In the 1930s, Scott Laboratories was commissioned by the Kenyan government to conduct research on coffee breeding and classification, attempting to find varieties that could adapt to Kenya's terroir, be used for large-scale planting, and have commercial value. SL-28 and SL-34 were two of many research results. The organization was active from the 1930s to the 1960s, but no longer exists today.

The SL series was researched and bred based on the ancient Yemeni Mocha variety and the Bourbon variety from Réunion Island. Today it accounts for most of Kenya's coffee production. Relatively speaking, SL-28 has gained higher prestige, while SL-34 has larger yields and is planted at slightly lower altitudes. According to SL laboratory botanists, SL28 and SL34 are genetic variants. Among them, SL28 has a mixed lineage of Mocha and Yemeni Typica. The original goal of cultivating SL28 was to mass-produce coffee beans that combined high quality with resistance to pests and diseases.

Although SL28's yield later did not reach the expected high volume, because of its bronze leaf color and broad-bean-shaped seeds with excellent sweetness, balance, complex and changeable flavors, and notable citrus and smoked plum characteristics, it has been passed down to this day. This is also the main reason why Front Street Kenya coffee is rich in pleasant acidity.

SL34 is similar in flavor to SL28. In addition to complex and changeable acidity and a great sweet finish, its mouthfeel is heavier, richer, and cleaner than SL28. SL34 has Bourbon and more Typica lineage. Its bean appearance is similar to SL28, but it survives better, for example adapting to sudden heavy rain.

Ruiru11

Ruiru appeared after SL28 and SL34. According to Front Street's understanding, in the 1970s, the Ruiru station began trying to cultivate different CBD and rust-resistant varieties. The result was Ruiru11, released in the 1980s. High yield, along with CBD and rust resistance, seemed to be the solution to all of Kenya's coffee production problems.

Batian

The Batian variety was released by the Coffee Research Institute (CRI) on September 8, 2010, and is also the newest variety provided by Kenya. It was a further experiment based on lessons learned from Ruiru11. Genetically, it is essentially selected from backcrosses of SL28 and SL34, and is also closer to SL28 than Ruiru 11. This thereby eliminated the problematic Robusta variety coffee bean elements, improving cupping quality.

Kenyan coffee bean grading system Kenya grades coffee by bean size and cupping results. According to coffee bean size, shape, and hardness, from high to low they are AA or AA+, AB, PB, C, E, TT, T. For green coffee beans of the AA and AB grades, an additional special grading based on cupping results is added (not officially recognized by the Kenyan state, but established by exporters), from high to low as TOP, PLUS (+), FAQ.

AA Plus (AA+): AA grade with particularly excellent cup quality (flavor, mouthfeel). AA beans: Screen Size 17–18 mesh. AB beans: Screen Size 15–16 mesh, accounting for most of production. C beans: Screen Size smaller than AB. TT: From AA and AB grade beans, lighter-weight beans blown out by an airflow sorter. T: From C grade beans, lighter-weight beans blown out by an airflow sorter. E Elephant Bean: Large mutated beans formed by two beans fused into one, also called Elephant ear. PB Peaberry: Classified by appearance, unrelated to flavor or weight.

As Front Street Coffee said above, whether it is the processing method or the coffee producing region and variety, all have more or less influence on the flavor of coffee beans. The Kenyan producing region itself is very suitable for growing coffee beans, and the developed K72 washed processing further adds to the flavor of the coffee beans. Multiple washings also make the coffee bean flavor cleaner and brighter. This is also why Kenyan coffee beans all have bright fruity acidity similar to cherry tomatoes.

Next, Front Street will introduce to all coffee fans the current Front Street Kenyan coffee beans and the roasting and brewing data analysis from Front Street Coffee.

Front Street Coffee Kenya Asalia Coffee Beans

Country: Kenya Region: Asali (Honey Processing Station) Altitude: 1550-1750m Variety: SL28, SL34 Processing method: 72-hour washed processing Flavor: Snow pear, smoked plum, yellow sugar, cherry tomato, plum

Front Street Coffee Kenya Asalia Coffee Bean Roasting Record

This Front Street Kenya bean is full and round. In order for Front Street Coffee to fully express its bright, mellow acidity, the roast level used by Front Street Coffee is a light roast. Yangjia 800N semi-direct fire, bean charge 480g: charge at a drum temperature of 160°C, airflow opening 3, heat 120. Turning point: 1'28". When the temperature rises to 130°C, airflow opening 4. Roast to 6'00'', temperature 154.6°C, bean surface turns yellow, grassy smell completely disappears, dehydration completed. When the bean surface shows ugly wrinkles and dark streaks, and the toast smell clearly turns into coffee aroma, it can be defined as the prelude to first crack. At this time, listen clearly for the sound of first crack. First crack begins at 9'28'', airflow unchanged, first crack development time 2'20'', drop at 193.8°C.

Front Street Coffee Brewing Suggestions

Dripper: Hario V60 Water temperature: 90°C Dose: 15 grams Coffee-to-water ratio: 1:15 Grind size: fine granulated sugar (80% passing through China standard No. 20 sieve)

Front Street Coffee brewing method: Use 30 grams of water for a 30-second bloom, pour in a small stream in circles to 125 grams for a split, and when the water level is about to expose the coffee bed, continue pouring to 225 grams and stop. When the water level is about to expose the coffee bed again, remove the dripper. (Start timing from the beginning of the bloom.) Extraction time is 2'00".

[ Front Street Coffee Kenya Asalia] Flavor description: Wet aroma has ripe tomato and floral notes. On the palate, flavors of cherry tomato and smoked plum, bright acidity, clean and rich mouthfeel, prominent sweetness in the middle, juicy, with a finish of berry aroma and yellow sugar sweetness, plus green tea aroma.

Front Street Coffee Kenya Sachini Estate PB Coffee Beans

Country: Kenya Region: Sachini Estate Altitude: 1680m Variety: SL28, SL24, riuru Processing method: 72-hour washed processing Flavor: Cherry tomato, almond, smoked plum, honey, grape

Front Street Coffee Kenya Sachini PB Coffee Beans Roasting Analysis

Because this rich Front Street Kenya coffee bean comes from a higher altitude, its bean quality is harder. It initially climbs with a relatively high rate of temperature rise, with the yellowing point at around 5 minutes, then lowers heat to enter the Maillard reaction. At 166°C, heat is lowered again to extend the Maillard reaction time. When first crack begins, heat absorption is stronger, so it is recommended to maintain heat at this stage to prevent stalling. First crack development takes more time, which helps reduce acidity and develop flavor.

Roaster Yangjia 800N (roasting amount 300 grams)

Charge at a drum temperature of 170°C, heat 100, airflow opening 3; turning point 1'42", when drum temperature is 140°C open airflow to 3.5, heat unchanged; when drum temperature is 149°C the bean surface turns yellow, grassy smell completely disappears, entering the dehydration stage;

7'14'' dehydration completed. Heat and airflow unchanged. At 7'30'' wrinkles and dark streaks appear on the bean surface, and the toast smell turns into coffee aroma, as the prelude to first crack. At this time, pay attention and listen for the sound of first crack. First crack begins at 8'20'', airflow opening 4, heat lowered to 50. Post-first-crack development time 1'50'', at 188°C heat lowered to 30 to flatten the rate of temperature rise, drop at 193.3°C.

Front Street Coffee Brewing Suggestions

Dripper: V60 or cake cup Water temperature: 90-91°C Coffee-to-water ratio: 1:15 Grind size: fine grind (80% passing through China standard No. 20 sieve)

Brewing method: staged extraction. Use 30 grams of water for a 30-second bloom, pour in a small stream in circles to 124 grams for a split, and when the water level is about to expose the coffee bed, continue pouring to 228 grams and stop. When the water level is about to expose the coffee bed again, remove the dripper. (Start timing from the beginning of the bloom.) Extraction time is 1'55".

[ Front Street Coffee Kenya Sachini PB] Flavor and mouthfeel:

When brewed with a V60 dripper, it smells floral. On the palate there is acidity of cherry tomato, citrus, and nuts. In the middle there is creamy aroma, brown sugar sweetness, and a finish of cocoa and oolong tea. The flavor layers are relatively rich and the floral aroma is obvious. When brewed with a cake dripper, it smells of herbal plant aroma and cherry tomato aroma, with an overall obvious juicy feel and a relatively lively acidity.

The above content is compiled by CoffeeHunters, a coffee news website.