Front Street Coffee (FrontStreet Coffee) has always emphasized that the extraction parameters of pour-over coffee have a great impact on a cup of coffee, and forespressothe impact on extraction is even greater. You should know that factors such as the concentration and extraction time of espresso are more demanding than those of pour-over coffee. A slight deviation will be magnified exponentially in the flavor of a cup of espresso. Therefore, understanding the extraction parameters of espresso is truly very important.
 
First, just like the extraction parameters of pour-over coffee, espresso pays even more attention to extraction parameters. The following will separately explain and analyze coffee dose, brew ratio, extraction time, flow rate, extraction pressure, and extraction temperature.

 
Coffee dose
The amount of coffee grounds is determined by the capacity of the filter basket. Some coffee machine manufacturers provide double filter baskets in several capacity specifications such as 16g, 18g, 20g, and 22g, and these specifications are recommended capacities, with the maximum allowable filling dose error being less than 1g. For example, with an 18g filter basket, a reasonable dose range can be 17-19g.
 
Front Street does not recommend a dose much smaller or much larger than the filter basket size. The dose affects the density of the coffee puck. Under the same tamping force, too little coffee grounds will be looser, causing the flow rate to be faster and leading to under-extraction. Conversely, too much will make the density more compact, the flow rate slower, or even make it difficult to extract coffee liquid.

Brew ratio
Espressouses the ratio of coffee grounds to espresso liquid, because you cannot calculate how much water was used for extraction. Of course, some new coffee machines install a flow meter at the water inlet to display the water volume. The earliest extraction ratio was the single-shot espresso standard, extracting 25-30ml of espresso liquid from 7-8g of coffee grounds. The former is a unit of weight, and the latter is a unit of capacity (volume). Only when the density is consistent are the two equivalent. But we all know that the extracted espresso has golden crema, and the thickness of this crema depends on the roast level and freshness of the coffee. Therefore, using this measurement method will cause inconsistency in the final product.
 
Thus the ratio of coffee dose to liquid yield appeared. It is generally between 1:1.5 and 1:2.5, and a 1:2 ratio is more commonly used, such as extracting 40g of espresso liquid from 20g of coffee grounds. The ratio is affected by two factors: one is the dose, and the other is the water amount. Too low a ratio will make the coffee taste very rich and heavy, and it is prone to the bitter taste brought by over-extraction. Conversely, too high a ratio will make it taste weak and insipid, as well as sharply sour due to under-extraction.

Extraction time  
Time refers to the entire extraction time from locking in the portafilter and pressing the extraction button to the end of extraction. The factors affecting extraction time are one, the grind size, and the other, the ratio. The ratio is easier to understand: with a higher ratio, more water is needed for extraction, so the time naturally becomes longer. Grind size affects the coarseness or fineness of the coffee grounds, and the degree of coarseness or fineness directly affects the compactness of the coffee puck. The finer the coffee grounds, the denser the puck after tamping, making it difficult for water to pass through, and the time will be prolonged, easily leading to over-extraction. Generally speaking, the time to extract one espresso is about 20-30 seconds.

Flow rate
Flow rate is the speed at which the coffee liquid flows down. The ultimate goal of our extraction parameters is actually the result of the flow rate. For normal espresso, the first drop of coffee liquid should begin to fall about five seconds after pressing the extraction button, and the subsequent flow rate should be relatively even. The speed of the flow rate directly reflects whether the grind size and ratio are appropriate. If it takes more than 10 seconds (excluding pre-infusion) for the first drop of coffee liquid to appear, then the coffee may be too fine, or the tamping may be too compact. If the flow rate is too fast or there is spraying, then the coffee is too coarse, or channeling has occurred.
 

Extraction pressure
Generally speaking, the extraction pressure of a semi-automatic coffee machine is around 9 bar, which is determined by the performance of the coffee machine. Some coffee machines now have pressure-profiling extraction functions. Low pressure leads to low extraction efficiency, while high pressure leads to high extraction efficiency.

Extraction temperature
The water temperature for extracting espresso is generally between 90 and 94 degrees Celsius. If the water temperature is too high, over-extraction is likely, and the coffee taste is prone to bitterness. If the water temperature is too low, under-extraction is likely, resulting in a sharply sour coffee taste.
 
So what details should be paid attention to when making espresso?
Makingespressocan be roughly divided into several main parts: weighing the grounds, distributing the grounds, tamping, machine extraction, and cleaning. Front Street has also mentioned before that distributing and tamping are very important for a cup of espresso. Other factors have secondary influence on a cup of espresso, but they also have an impact that cannot be ignored.

 
There are two points to note in weighing the grounds: one is the influence of retained grounds, and the other is the accuracy of the dose. Carefully observe your espresso grinder. Whether it is a hopper type or direct-output type, there is a channel between the burrs and the discharge port, and this channel accumulates previously ground coffee. If too much time has passed since the last grinding, the flavor of the coffee grounds in the channel is almost gone. At this time, you should use a tool to empty the coffee grounds in the channel, or start the grinder and let the subsequent coffee grounds push out the previous coffee grounds, then discard them. Then grind and dose.

Taking the Faema 900N grinder used by Front Street Coffee (FrontStreet Coffee) as an example, the coffee retained in its channel weighs as much as 2 grams. If a double espresso uses 20 grams of coffee grounds as an example, this accounts for one-tenth of the dose, showing how great the impact is.
 
Then there is the issue of weighing accuracy. Taking the Faema 900N as an example, the version used by Front Street is non-quantitative, which requires a highly sensitive electronic scale for assistance. In order to produce accurately and consistently, the grounds should be weighed for every extraction. Front Street recommends that the maximum error be within plus or minus 0.1 grams.

If you are using a quantitative grinder, please do not ignore this issue either. At present, most quantitative grinders use timing as their principle (though there are exceptions), and the problem caused by timing is that inconsistent rotation speed, different hopper pressure, and varying coffee bean size and density create errors in the grinding amount.
 
Inconsistent rotation speed: The reason for inconsistent rotation speed is related to voltage. Domestic voltage fluctuates at 220V plus or minus 10V. When the voltage is high, the rotation speed is fast; when the voltage is low, the rotation speed is slower.
 
Different hopper pressure: Each time you grind, a different amount of coffee beans stored in the hopper will lead to inconsistent hopper pressure. When the hopper pressure is unstable, it will also affect differences in the output dose.
 
Varying coffee bean size and density: There are differences in size and hardness among the varieties in a blend. Each time you grind, the proportion of varieties is different, and this situation will also cause differences in dose.

Extraction should be methodical, from grinding the beans to receiving the grounds, distributing the grounds, tamping, then locking on the portafilter and pressing the extraction button. Theoretically, this set of actions is continuous and should not be interrupted. Therefore, before grinding, think clearly about what you are going to do next and what has not been prepared yet. If you are still unfamiliar with the operation, you can practice it multiple times; practice makes perfect.
 
Develop the good habit of cleaning. First, a clean environment gives people a sense of comfort. Second, cleaning key parts will affect the quality of the next cup of coffee, such as the retained grounds in the grinder chamber mentioned above. Also there are retained grounds on the distribution tool and tamper. Moreover, ensure that the distribution tool, tamper, filter basket, and other utensils that directly contact coffee grounds are dry (in plain terms, do not let water remain on these utensils), and rinse and clean them after each use.

After extracting a cup of espresso, remember to clean the portafilter and group head as you go (no matter how busy you are). These seemingly unimportant coffee grounds will affect the quality of the next cup of espresso.

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