How Does Kenya's Coffee Grading System Fit K72 Washed Beans?

Kenyan coffee stands out for bright fruit acidity and a clean mouthfeel, and the K72 washed processing method and the SL28 and SL34 varieties are central to that. K72 is a 72-hour cyclic fermentation: cherries are pulped, fermented 24 hours, rinsed with clean river water, then fermented and rinsed again across three cycles.

Kenya's highland growing conditions and its coffee grading system help explain the distinctive cherry tomato acidity buyers associate with the country. Beyond SL28 and SL34, improved varieties such as Ruiru11 and Batian are also planted. Processing starts on harvest day with water-based density sorting, where heavier, denser, fully ripe cherries sink and lighter ones float before fermentation.

Kenyan coffee is famous for its bright fruit acidity and clean mouthfeel, and the K72 washed processing method along with the SL28 and SL34 varieties play an indispensable role in this. From the perspective of Front Street Coffee, this article sorts out the 72-hour cyclic fermentation process of the K72 processing method, analyzes Kenya's highland growing conditions, the origins of the SL series varieties and their flavor differences, and introduces improved varieties such as Ruiru11 and Batian. It also organizes Kenya's coffee grading system, and includes the roasting and brewing data for Front Street Kenya Asalia and Sachini PB, helping coffee enthusiasts understand the causes behind Kenyan coffee's unique cherry tomato acidity.

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The specialty coffee market continues to expand, and the processing methods coffee fans encounter are no longer limited to natural and washed. The Kenyan K72 washed processing method, improved on the basis of traditional washing, is quite distinctive. In this article, Front Street Coffee (FrontStreet Coffee) will explain the specific operational process of Kenya's K72 processing method.

What is Kenya's K72 washed processing method?

As Front Street Coffee (FrontStreet Coffee) mentioned above, this processing method originated from improvements on traditional washing. Kenya was the first to adopt the practice of washing after fermentation and repeating the cycle: processing begins on the day of harvest, the best coffee cherries are selected, pulped, and fermented. The first round of fermentation lasts 24 hours, after which they are rinsed with clean river water. Then they are fermented again with clean river water for 24 hours and rinsed, repeating three cycles for a total duration of 72 hours, hence the name Kenyan-style 72-hour fermentation washed processing method, or K72 for short.

K72 fermentation washed processing method process:

① First washing and fermentation

After the coffee cherries are harvested, they first undergo water-based density sorting, using differences in fruit density and mass to screen them; beans with high density, that is, heavier beans, sink in the water, while those with low density float. Fully ripe fruit of excellent quality has higher density, and these are selected for subsequent processing.

After selecting high-quality, sufficiently ripe fruit, the skin is removed and they are washed and soaked, causing the mucilage attached to the outer layer of the green beans to ferment. The mucilage contains natural sugars and alcohols, which are key to the development of coffee sweetness, acidity, and overall flavor. The first round of fermentation lasts as long as 24 hours, removing 80% to 90% of the mucilage and preserving only the flavor within the bean.

② Second washing and fermentation

Next comes the second round of washing and fermentation, in which the cleaned coffee beans from the previous stage are soaked in water again for 24 to 48 hours. This process increases proteins and amino acids, giving the coffee acidity a complex and delicate layering. Finally, the remaining mucilage is removed, and the beans are moved to raised drying racks for sun drying.

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

Front Street believes that coffee beans processed with Kenya's 72-hour fermentation washed method are fermented at low temperatures for a long time and then dried and dehydrated to completion, which can give the beans a brighter, cleaner, and fuller flavor.

Kenya's coffee growing conditions

Of course, the quality of a coffee bean cannot be determined by the processing method alone; more critical is whether the bean itself is robust enough. Front Street Coffee (FrontStreet Coffee) has often mentioned in previous articles that coffee flavor depends on origin, variety, and processing method, which is to say that the role of the processing method is built on the premise of high-quality fruit.

Kenya is located in eastern Africa, with the equator crossing its center and the East African Rift Valley running north to south through the country. 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 is mostly highlands, with an average elevation of 1,500 meters. Mount Kirinyaga in the center, namely Mount Kenya, has an elevation of 5,199 meters and snow on its summit, making it the second highest peak in Africa.

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

Front Street Coffee (FrontStreet Coffee) also often says that the growing conditions of Arabica coffee beans are inevitably limited by altitude. The higher the altitude, the better the flavor and the richer the acidity, which is why Kenyan coffee is known 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 (FrontStreet Coffee) in-store Front Street Ethiopian coffee beans are known for their bright citrus-lemon acidity, while Front Street Kenya's acidity is more of a cherry tomato acidity, which brings us to the flavor of its coffee varieties.

Kenyan coffee bean varieties

The main varieties grown in Kenya are SL-28, SL-34, Ruiru11, and Batian. According to Front Street Coffee's (FrontStreet Coffee) understanding, these varieties are all research achievements of the Kenya Coffee Research Institute.

SL-28, SL-34

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

The SL series was bred from the ancient Yemen Mocha variety and the Bourbon variety of Reunion Island, and now accounts for the majority of Kenya's coffee production. Relatively speaking, SL-28 has gained a higher reputation, while SL-34 has larger yields and is grown at slightly lower altitudes. According to SL laboratory botanists, SL28 and SL34 are genetic variants. Among them, SL28 has mixed ancestry of Mocha and Yemen 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 volume, because of its bronze leaf color and broad-bean-shaped beans with excellent sweetness, balance, complex and varied 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 Kenyan coffee is rich in pleasant acidity.

SL34 is similar in flavor to SL28. In addition to complex and varied acidity and a wonderful sweet finish, its mouthfeel is heavier and more intense than SL28, and also cleaner. SL34 has Bourbon and more Typica ancestry. Its bean appearance is similar to SL28, but it is more able to survive, 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 breed 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 offered by Kenya. It was the result of further experimentation 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 eliminated the problematic Robusta coffee bean elements, thereby improving cup quality.

Kenyan coffee bean grading system

Kenya grades coffee by bean size and cup test results. According to bean size, shape, and hardness, from high to low they are AA or AA+, AB, PB, C, E, TT, T. For AA-grade and AB-grade green coffee beans, a special grading based on cup test results is added (not officially recognized by the Kenyan state, but set by exporters), from high to low: TOP, PLUS (+), FAQ.

AA Plus (AA+): AA grade with particularly excellent cup quality (flavor, mouthfeel).

AA beans: size (Screen Size) 17–18 mesh.

AB beans: size (Screen Size) 15–16 mesh, accounting for most of production.

C beans: size (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: a large mutated bean formed by two beans joined together, also called elephant ear.

PB Peaberry: classified by appearance, unrelated to flavor or weight.

As Front Street Coffee (FrontStreet Coffee) says, whether it is the processing method, coffee origin, or variety, all have more or less influence on the flavor of coffee beans, and the Kenyan origin itself is very suitable for growing coffee beans. The developed K72 washed processing also adds even more brilliance to the flavor of the coffee beans, and multiple washings also make the coffee bean flavor cleaner and brighter. This is also why Kenyan coffee beans all have bright fruit acidity similar to cherry tomatoes.

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

Front Street Coffee (FrontStreet 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 (FrontStreet Coffee) Kenya Asalia coffee bean roasting record

This Front Street Kenyan bean has a plump and round body. In order for Front Street Coffee (FrontStreet Coffee) to fully express its bright and mellow acidity, the roast level used by Front Street Coffee (FrontStreet Coffee) is a light roast. Yangjia 800N semi-direct fire, bean charge 480g: charge at a furnace temperature of 160°C, air damper set to 3, firepower 120. Turning point: 1'28". When the temperature rises to 130°C, set the air damper to 4. Roast until 6'00'', temperature 154.6°C, the bean surface turns yellow, the grassy smell completely disappears, and dehydration is complete.

When ugly wrinkles and dark streaks appear on the bean surface, and the toast aroma clearly turns into coffee fragrance, this can be defined as the prelude to first crack. At this time, listen carefully for the sound of the first crack point. First crack begins at 9'28'', the air damper remains unchanged, first crack development time is 2'20'', and the beans are dropped at 193.8°C.

Front Street Coffee (FrontStreet Coffee) brewing recommendation

Dripper: Hario V60

Water temperature: 90°C

Dose: 15 grams

Coffee-to-water ratio: 1:15

Grind size: fine granulated sugar (80% passing through Chinese standard No. 20 sieve)

Front Street Coffee (FrontStreet Coffee) brewing method: use 30 grams of water for a 30-second bloom, then pour in a small stream in circles until 125 grams for a staged pour. When the water level drops and is about to expose the coffee bed, continue pouring until 225 grams and stop pouring. When the water level drops and is about to expose the coffee bed, remove the dripper. (Timing starts at the beginning of the bloom) Extraction time is 2'00".

[Front Street Coffee (FrontStreet Coffee) Kenya Asalia] Flavor description: the wet aroma has ripe tomato and floral notes; on the palate there are flavors of cherry tomato and smoked plum, with bright acidity and a clean, rich mouthfeel. The mid-palate has prominent sweetness with a juicy feel, and the finish has berry aroma, yellow sugar sweetness, and green tea fragrance.

Front Street Coffee (FrontStreet Coffee) Kenya Sachini Estate PB coffee beans

Country: Kenya

Region: Sachini Estate

Altitude: 1680m

Variety: SL28, SL24, ruiru

Processing method: 72-hour washed processing

Flavor: cherry tomato, almond, smoked plum, honey, grape

Front Street Coffee (FrontStreet Coffee) Kenya Sachini PB coffee bean roasting analysis

This rich Front Street Kenyan coffee bean, due to its higher altitude, has a relatively hard bean quality. It climbs with a relatively high temperature rise at the beginning, with the yellowing point at around 5 minutes, then lowers firepower to enter the Maillard reaction, and at 166°C lowers firepower 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 a relatively long time, which helps reduce acidity and develop flavor.

Roaster Yangjia 800N (roast batch 300 grams)

Charge at a furnace temperature of 170°C, firepower 100, air damper set to 3; turning point 1'42". When the furnace temperature is 140°C, open the air damper to 3.5, firepower unchanged; when the furnace temperature is 149°C, the bean surface turns yellow, the grassy smell completely disappears, and it enters the dehydration stage;

At 7'14'' dehydration is complete, firepower and air damper remain unchanged. At 7'30'' wrinkles and dark streaks appear on the bean surface, and the toast aroma turns into coffee fragrance, as the prelude to first crack. At this time, pay attention to listening for the sound of first crack. First crack begins at 8'20'', open the air damper to 4, and lower firepower to 50. After first crack, development time is 1'50''. At 188°C lower firepower to 30 to flatten the temperature rise, and drop the beans at 193.3°C.

Front Street Coffee (FrontStreet Coffee) brewing recommendation

Dripper: V60 or cake cup

Water temperature: 90-91°C

Coffee-to-water ratio: 1:15

Grind size: fine grind (80% passing through Chinese standard No. 20 sieve)

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

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

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

For more specialty coffee beans, please add the private WeChat of Front Street Coffee (FrontStreet Coffee), WeChat ID: kaixinguoguo0925

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