If you often read Front Street’s articles, you should be familiar with the brewing time of “2 minutes”. It is a reference value based on countless past extraction experiences and can help us judge the speed of the flow rate.
Recently, a friend bought a bunch of different types of beans at a Front Street store and curiously asked: He extracts according to the parameters we provide every time, but why some coffee beans flow very fast when brewing, and all the liquid has dripped into the pot in less than 2 minutes; some coffee beans are like the "enemy", and they will accumulate water for a long time every time they are brewed. I don't know whether to cut off the flow or wait until the water runs out.
Let’s first take a look at the main factors that affect the flow rate of different coffee beans:
1. Baking degree
The lighter the roasting degree, the shorter the heating time of the coffee beans and the higher the internal density. This results in a tighter powder layer structure and smaller gaps for hot water to flow through during extraction, which makes them easier to block. In addition, the texture of lightly roasted coffee beans is crisper, and at the same grinding scale, more ultra-fine powder will be "exploded". This is also one of the important reasons why hand-made shallow roasted beans are always "flooded".
As the roasting degree deepens, the coffee beans continue to expand, and the density of the internal structure becomes lower. The ground powder layer is loose and even, providing a larger gap for hot water, which allows the coffee liquid to pass smoothly to the lower pot, so the overall extraction time of medium to dark roasted beans will be better than that of light roasted beans.
2. Treatment method
Washing, sun-drying, and honey processing are classified as three traditional processing methods. The coffee beans do not receive much external intervention during the processing, so the structure retains the original density. In contrast, the "non-traditional processing methods" are typically represented by the anaerobic fermentation process.
Anaerobically treated coffee beans will be fermented in a sealed barrel under controlled temperature. The decomposition rate of pulp and pectin is reduced, which prolongs the fermentation time, thereby allowing the coffee beans to derive more fruit flavor and fermented wine aroma. Compared with the three major traditional coffees, the anaerobic process will reduce the tightness of the coffee bean cell wall, so the internal structure will become very loose after roasting, and it can rotate easily and smoothly when grinding.
The Front Street Chiclaw coffee that uses double anaerobic sun-drying is a very successful performance. The low-temperature fermentation step greatly improves the sweetness of the Chiclaw, making the aroma of passion fruit, grapes, and dried blueberries clearer. Although Front Street Xizu also uses medium-light roasting, it can be found that the extraction speed is obviously much faster than ordinary sun-dried beans and washed beans, and it is easy to under-extract if you are not careful.
3. Planting altitude
In the introduction of all single-origin coffee beans, the place of origin, manor, processing method, altitude, variety... These basic information are often affected by the purchase demand, and few people pay attention to the reference indicator of "planting altitude". But Front Street wants to tell you that if you want to comprehensively analyze the flow rate problem, the answer may be hidden in the altitude.
Friends who have studied geography know that for every 100 meters of elevation, the temperature drops by 0.6°C. Therefore, the higher the altitude of coffee trees, the lower the temperature will be, and the growth and maturity of the fruits will also be delayed. This not only helps the coffee beans store more aroma precursors, but also makes them harder.
For example, the Ethiopian production areas that Front Street likes very much are mostly produced at altitudes above 2,000 meters, such as Front Street Guodingding (2,100 meters), Front Street Gesha Village Red Label (2,069 meters), Front Street Oiran (2,350 meters), and other medium-light roasted beans that feature floral aroma and fruit acidity. Due to their high hardness, the flow rate during brewing slows down, and coffee that is seriously "overtime" will either be over-extracted or have unclear flavor.
After talking about the reasons, let’s analyze the solutions:
Now that everyone knows that the hand-brew flow rate of different coffee beans is affected by the above three aspects, then to set the extraction time to the ideal value only requires detailed analysis of the specific situation.
Flow rate too fast: anaerobic treatment, dark roasting
If you brew anaerobic coffee beans at a ridiculously fast speed and have little aroma, there is a high probability that the extraction is insufficient. It is best to adjust the grinding speed directly. Front Street coffee brewing usually only uses 2 to 3 grinding scales, with light roasting being the finest and dark roasting being the coarsest. In order to lock in hot water, anaerobic coffee will be 0.5 grid finer than light roasted beans (hand grinding can be finer by 1 to 2 grids). At the same time, in order to make the extraction time more sufficient, Front Street will control the water flow to be smaller when filling the water, so there is no need to raise the powder layer too high. In this way, the coffee brewed will have a richer and fuller flavor.
When you are brewing dark roasted beans, the time is always less than 1 minute and 40 seconds, and the taste lacks mellowness. The problem is probably the lack of support from the tail material. Considering that dark-roasted beans contain more caramel-like substances, finer grinding will easily release too much bitterness. Therefore, Front Street recommends dividing the total water volume into four sections. After steaming, use small water flow to inject in a circle throughout the process. Friends who have the conditions can replace the slow-flow filter cups such as KONO, cake cups, and Kalita, which can lengthen the overall soaking time. If you feel that it is over-extracted, you can lower the water temperature by 1~2℃ and try again.
Flow rate too slow: Lightly roasted beans at high altitude
On weekdays, Front Street recommends using a combination of "high water temperature, fine grinding, and fast flow rate" when shallow roasting beans. In this case, fine grinding is the main culprit of slow flow rate. There are two solutions to the problem here, either adjust the coarse grinding degree, or change the method and then lower the water temperature.
If you spend an exaggerated amount of time every time you brew shallow roasted beans, and the taste is mainly astringent, thin, and pungent, Front Street recommends that you adjust the grinding scale by 3 to 4 notches. This can directly change the particle size and reduce the distribution of extremely fine powder. It also reduces the contact area with hot water, allowing the coffee liquid to flow faster.
Without changing the grinding degree, if you want to speed up light roast coffee, you can also rely on adjustment techniques. Generally, after steaming, the Front Street continues to increase the circle range when filling water until the powder layer is piled up to 4/5 of the filter cup. The purpose is to let the large particles drive the fine powder to distribute on the edge of the filter cup first, providing a smooth channel for the subsequent injection of hot water. Wait until all the coffee liquid is almost finished before continuing to inject the third section of hot water. This reduces the probability of clogging and is more conducive to subsequent even extraction.
Finally, if adjusting the grinding degree and technique cannot improve the water accumulation problem of hand brewing, Front Street recommends that you do not interfere with the brewing time, but try the effect by lowering the water temperature. For example, whenever brewing Front Street Gesha Village Gold Label, if you use fine grinding, it is easy to over-extract due to "timeout", so Front Street had an idea and adjusted the water temperature to 86℃, the extraction was completed in 2 minutes and 32 seconds. Not only did the coffee have no negative taste, it also showed rich fresh citrus aroma and black tea flavor. It can be seen that there is no universal formula for hand brewing, only proper extraction management.
