What Causes Under-Extraction in Pour-Over Coffee: Solving the Root Problems

The Art of Pour-Over Coffee: A Journey into Perfect Extraction

What could be better than starting a new day with a delicious cup of coffee? When I first started making my own coffee, I was afraid it would become too bitter and difficult to swallow, so I settled for making coffee that was as weak as water. After drinking this type of coffee for a long time, I soon lost my desire for pour-over coffee. Therefore, to enjoy a good cup of coffee, basic knowledge of pour-over coffee is essential.

Understanding the Golden Cup Theory

The Golden Cup extraction theory is a concept known to many coffee enthusiasts but not well understood. According to SCAA Golden Cup standards, the optimal extraction range for coffee is between 18% and 22%, while the optimal concentration is between 1.15% and 1.35%. However, taste is quite subjective, and not everyone likes coffee that meets Golden Cup standards. This is merely a reference.

Before explaining the causes of under-extraction, FrontStreet Coffee would like to guide everyone through the process of making a cup of pour-over coffee. Let's take the Guohuai 5.0 from FrontStreet Coffee's bean menu as an example. As usual, we need to first understand the information behind this pour-over coffee bean:

The Story of Guohuai 5.0

Guohuai 5.0 is a natural single-origin coffee bean from the Hambela sub-region of the Sidamo region in Ethiopia. The Sidamo region is one of the main areas in Ethiopia that produces specialty coffee beans, with cultivation altitudes between 1,900 and 2,200 meters. Compared to washed beans, natural processed Sidamo coffee beans are more famous. Coffee enthusiasts often compare washed Yirgacheffe coffee with natural processed Sidamo coffee.

The Guohuai coffee bean won the championship in the natural category of the 2017 TOH green bean competition. A Beijing-based green bean merchant imported this coffee bean. African coffee beans are typically named after their production area or processing station. Due to the outstanding flavor of this coffee bean and the high expectations of the green bean merchant, it was named "Guohuai," meaning the leader of all flowers. In the same year, at the China region of the World Brewers Cup, when Geisha coffee beans dominated many competitions, contestant Li Jianfei used the same batch of Guohuai coffee beans to defeat multiple contestants and ultimately achieved second place. Since then, Guohuai has been named according to the year as Guohuai X.0. By the 2021 production season, it naturally became Guohuai 5.0.

FrontStreet Coffee Ethiopia Sidamo Guohuai 5.0
Region: Sidamo Region, Ethiopia
Processing Station: Buku Able
Altitude: 2,350 meters
Variety: Local native varieties
Processing Method: Natural processing

Brewing Parameters for Guohuai 5.0

When FrontStreet Coffee brews this Guohuai 5.0, considering that the coffee beans are lightly roasted, and the dissolution rate of substances in lightly roasted coffee beans is slower, higher water temperature is used to accelerate the dissolution of substances, and a finer grind is used to increase the contact area between coffee powder particles and water. At the same time, to avoid over-extraction due to too slow flow rate, a faster flow rate dripper such as Hario's V60 will be used.

Dripper: Hario V60
Water Temperature: 92 degrees Celsius
Coffee Amount: 15 grams
Coffee-to-Water Ratio: 1:15
Grind Size: 80% pass-through rate on China standard #20 sieve

First, pour 30 grams of water to completely wet the coffee grounds, then start from the center point with a small water stream and slowly circle until reaching 125 grams for segmentation. When the water level in the dripper drops to just about to expose the coffee bed, continue pouring water. The third segment of water also starts from the center point, then slowly circles until reaching 225 grams and stop pouring. When the water in the dripper has completely dripped into the sharing pot below, remove the dripper. The total extraction time is approximately 2 minutes.

Understanding Extraction Failures

A very important factor in extraction failure is the mismatch between coffee grind size and extraction time and method. The grind size of coffee can expose all volatile aromatic compounds in the coffee beans. Grind size will have a significant impact on your coffee extraction. Everyone knows that over-extracted coffee is bitter and astringent, making it difficult to swallow; while under-extracted coffee tastes as plain as water, with prominent sharp acidity and a disappointingly short aftertaste.

Although you can just throw roasted coffee beans into water and coffee will begin to extract, this takes quite a long time. However, as we grind the coffee particles finer, the surface area of the coffee particles will double, and the larger the contact area with water, the more substances that can be dissolved after water comes into contact with coffee, and the corresponding extraction rate will increase.

The first and most important point is the grind size. Different roast levels of coffee beans need to match different grinds. Finely ground coffee particles may lead to over-extraction of coffee, leading us to the next important factor in coffee extraction—time. Large particles of coffee powder release flavors more slowly, while smaller particles release flavors faster. For example, when making coffee with a French press, long immersion extraction requires coarser coffee powder for extraction; most filter coffees use medium-fine grind particles.

Determining the Ideal Grind Size

So, how should the coffee grind size be determined? FrontStreet Coffee divides the pour-over coffee beans on its menu into three categories based on roast level: light roast, medium roast, and dark roast. FrontStreet Coffee also mentioned earlier that as the coffee roast level becomes deeper, the dissolution rate of coffee substances becomes faster. Therefore, to inhibit the too-fast dissolution rate, a coarser grind size will be used. FrontStreet Coffee's usual standard is:

Light roast corresponds to medium-fine grind size, which is 80% pass-through rate on China standard #20 sieve.

Medium roast corresponds to medium grind size, which is 75% pass-through rate on China standard #20 sieve.

Dark roast corresponds to medium-coarse grind size, which is 70% pass-through rate on China standard #20 sieve.

The above are reference standards only for pour-over coffee. Since the grind scale standards of coffee grinders sold on the market are different, it's like how EK43's #10 corresponds to what on a small Fuji? It's difficult to have a standard, so FrontStreet Coffee uses standard sieves for testing before cupping or brewing a coffee bean.

The Importance of Bean Freshness

The second point is the freshness of the coffee beans. As time goes by, the longer the roasted coffee beans are stored, the flavor of the coffee will change over time, so the extraction plan also needs to be adjusted accordingly. In this situation, some people prefer to grind finer, while others increase the amount of coffee powder and grind slightly coarser to adjust. The former increases the coffee extraction rate, while the latter relates to coffee strength.

Finer grinding has more coffee particles, which will bring the surface area in contact with water, increasing the extraction rate. However, not all flavor compounds are pleasant, so a higher extraction rate is not always ideal. The flavors we don't like dissolve the slowest, so controlling the dissolution rate of coffee through the grind setting is also something we need to pay attention to.

Conclusion: The Path to Perfect Extraction

When extracting coffee, uniform grinding is crucial to avoid uneven extraction due to inconsistent extraction times. Under-extraction also includes technique; if the technique is improper, the interaction between coffee powder and water is less active, which will also change the final extraction structure. Therefore, many factors affect whether a cup of coffee is well-extracted, as the saying goes, one wrong step leads to all steps wrong.

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Important Notice :

前街咖啡 FrontStreet Coffee has moved to new addredd:

FrontStreet Coffee Address: 315,Donghua East Road,GuangZhou

Tel:020 38364473