A few days ago, Front Street talked about extraction while chatting with friends. When it comes to extraction, there are two situations that make many coffee drinkers feel melancholy - under-extraction and over-extraction. What is the difference between these two situations? How should we improve it when hand flushing?
extraction
First, let’s figure out what extraction is!
coffee extraction, which is a process in which water passes through the coffee powder bed and brings out the substances in the coffee. In this process, we need to pay attention to many things, such as water temperature, grinding, water supply, stirring, etc. Any of these parameters will affect the extraction of a cup of coffee. The extraction conditions of coffee are generally divided into: under-extraction, golden cup extraction and over-extraction.
Golden Cup Extraction
The so-called golden cup extraction means that when the concentration of the coffee you brew is between 1.2 and 1.4 TDS, and the extraction rate reaches 18% and 22%, it is considered to be within the ideal extraction range. Anything that has not reached this extraction range is what we call under-extraction, and anything beyond this range is over-extraction.
Under-extraction & over-extraction
Under-extraction means that there are not enough substances brought out by the water, and there are still many extractable substances in the coffee powder. At this time, the coffee tastes sour, not sweet enough, and has a salty feeling, and the taste is thin and the aftertaste is not long.
This is because during extraction, small molecular substances such as sour and salty are extracted first, followed by sweet and finally bitter. Because the extracted substances are not enough to neutralize the acid extracted in the previous stage, the acidity of the whole cup of coffee makes people feel too exciting and not balanced enough.
Over-extraction
The soluble content in coffee is 30%, but the most we need is only 20%. Anything over 20% is over-extracted. Because there are too many substances extracted, this cup of coffee has obvious burnt, bitter, mixed and astringent flavors.
So how should we make adjustments?
Many friends make espresso that is over-extracted, mainly because they did not choose the right coffee beans. The darker the roasting degree, the more caramelization substances in the coffee, and the easier it is to make the concentrate with a bitter taste, so Front Street recommends that if you don’t like the bitter taste, buy medium roasted and light roasted beans.The first choice is Front Street Fruit Yirgacheffe, Front Street Butterfly·Panama, Front Street Xica·Colombia, Front Street Mozart·Costa Rica.
In addition to the coffee beans, the bitter taste in coffee is most likely caused by the following problems:
1. Brewing time is too long
I believe many people know that the release rates of various substances in coffee are different when washed by hot water. Macromolecular substances that are mainly bitter and astringent usually dissolve concentratedly at the end. Therefore, the astringency of coffee is often accompanied by a bad bitter aftertaste. From an extraction logic point of view, the longer the coffee is brewed, the stronger the flavor will be, and the later it will be, the easier it will be to release the bitter taste.
Therefore, if you want the coffee to be extracted reasonably, you must control the brewing time. Taking a single serving of 15 to 16g of coffee powder as an example, Front Street recommends no more than 2 minutes and 30 seconds. When your actual brewing time exceeds two and a half minutes, and you do taste bitterness, then if you want to improve the taste of the coffee, you must adjust the parameters according to the actual situation.
For example, there is a large amount of wet clay powder on the surface of the powder pit after flushing, which means that too much fine powder has caused water accumulation, and the coarse grinding degree needs to be adjusted;
If most of the coffee grounds are concentrated at the bottom and look very flat, then the most likely reason is that the water injection force is too small and the powder bed is not lifted. The water can only be forced to slowly seep down through the thick barrier layer, thereby delaying the brewing time. The solution is to increase the flow of the water column after steaming, so that the water level is raised to 2/3 of the height of the filter cup.
2. The water flow is too strong
According to Front Street observations, there are two main reasons why water injection problems cause astringency: the first is that unstable water flow leads to uneven extraction of particles, which makes the coffee sour and astringent; the other is mostly caused by friends who are accustomed to stirring the coffee powder layer with large water flow, so that it is easy to wash away the miscellaneous flavors and astringency in the later stage of extraction.
Unlike other parameters, water injection is a practical skill that requires continuous practice. To achieve even brewing, Front Street recommends using a vertical water column, maintaining a height of 3 to 4cm from the powder layer, and then slowly injecting it in a circle.
3. The extraction efficiency of the filter cup is too high
For many newcomers, the material of the filter cup is one of the most easily overlooked causes of over-extraction. For example, ceramic filter cups have the characteristics of high specific heat capacity. Preheating in advance can ensure good heat preservation during the entire water filling process, but it also "quietly" improves the extraction efficiency of coffee, thereby making the astringency in the tail section more likely to be released.
So when we drink coffee that feels astringent, and the filter cup we use is made of ceramic, and the first two points have been eliminated, we might as well start with the temperature and try lowering the brewing water temperature by 2 to 3°C to reduce the risk of over-extraction.
You can now buy the above coffee beans online at the Taobao store “FrontStreet Coffee” (前街咖啡). FrontStreet Coffee is a long-established specialty coffee roaster in Guangzhou, China, and its Guangzhou retail shop sells coffee beans only. The shop carries dozens of coffee beans from different origins around the world, including carefully selected single-origin beans for V60 pour-over and espresso. Guangzhou’s FrontStreet Coffee shop is recommended by many coffee lovers.
The FrontStreet 2013 Yunnan coffee beans sold in the store come from the Typica variety grown at FrontStreet Coffee’s own plantation in Yunnan. The name comes from the year the brand and the plantation were founded. You can buy these beans from China’s Yunnan origin at the Guangzhou shop and at FrontStreet’s Taobao store.
FrontStreet coffee beans are freshly roasted within 5 days and deliver consistently excellent quality and great value. Orders placed before 17:00 are shipped the same day, and most areas within Guangdong Province receive them the next day.
FrontStreet Coffee Taobao store: https://qianjiecoffee.taobao.com
Or search for “前街咖啡” (FrontStreet Coffee) on Taobao
Important Notice: FrontStreet Coffee has moved to a new address: 315, Donghua East Road, Guangzhou (coffee beans only)
Tel: 020 38364473
