Espresso extraction: how to make the perfect espresso
13. April 2020
Coffee-making experts will have already heard of espresso extraction. It is key to making the perfect tasting coffee. In this blog entry, we uncover the meaning of the term “espresso extraction” and let you in on the secret to preparing the perfect espresso.
What is espresso extraction?
When making coffee, extraction is the process of removing the aroma and flavour from the coffee grounds. Extraction occurs during brewing, whereby hot water acts as the extracting agent. The undissolved coffee grounds remain in the filter or strainer, while the aroma and flavour are released into the cup. If the extraction time is too short, then it is known as under-extraction. If the extraction time is too long, then the coffee is over-extracted.
When hot water and the grounds from roasted coffee beans come into contact, the extraction process begins and the water-soluble compounds dissolve in order of solubility. This occurs in three extraction phases.
The three extraction phases
The espresso extraction process can be divided into 3 phases, which each last approx. 8 seconds.
- Acids (seconds 1 to 8): In the first 8 seconds, the acids are extracted.
- Flavours and oil (seconds 8 to 16): In the next approx. 8 seconds, the aromatics are released.
- Bitter compounds (seconds 17 to 24): Then in the following 8 seconds, the bitter compounds are released and the crema appears. With its thick consistency and light brown colour, it is the first visual indication of a successful espresso.
The ideal espresso extraction time is between 20 and 30 seconds. The time that the espresso extraction process takes depends on the tamping, the quantity of coffee and the grind size.
Why is extraction so important in espresso preparation?
Coffee grounds are approx. 30% water-soluble. The remaining approx. 70% mainly consists of insoluble fibres. The espresso extraction process enables the right quantity of solubles to be removed from the coffee grounds. This quantity is called the extraction yield. The ideal extraction yield is about 18-22% of the soluble 30%. You might be wondering why making an espresso suddenly seems like a mathematical calculation. Here’s the answer to your question as to why espresso extraction is so important when preparing this classic variety of coffee. The espresso only achieves the right balance between bitter and sour tones when the extraction yield reaches the specified percentage. This balance gives the espresso its particularly delicious taste.
Espresso extraction step by step
- 1) Clean the portafilter: An espresso machine portafilter should always be clean and dry before preparing the next coffee. Used coffee ground residue negatively impacts on the flavour.
- 2) Grind fresh beans: There is a marked difference between using ready-ground coffee and beans that are freshly ground when required.
- 3) Distribute the coffee grounds evenly: The coffee should be distributed evenly in the filter basket. Otherwise, the espresso might be unevenly extracted.
- 4) Tamper: Use a tamper to evenly compress and compact the coffee grounds.
- 5) Clean the portafilter rim: The rim of the portafilter should be clean and free from coffee grounds before use. Otherwise, the excess coffee grounds can burn in the O-ring.
- 6) Clean the group head: The group head should be flushed through with water once and then wiped clean with a damp cloth before inserting the portafilter. This ensures that all of the excess coffee grounds are removed.
- 7) Insert the portafilter and start brewing: You can now insert the portafilter. Once the portafilter is inserted into the group head, the extraction process (i.e. brewing) should start straightaway. Otherwise, the ground coffee in the portafilter can burn, causing the espresso to taste bitter.
- 8) Observe the extraction time: The espresso should be extracted for between 20 and 30 seconds.
- 9) The right vessel: Selecting the right cup is also an important consideration! Our barista Daniel gives you a few quick tips in this youtube clip on how to choose the perfect espresso cup.
How to recognise espresso under-extraction and over-extraction
An under-extracted espresso can be identified by its watery taste, lack of flavour and a very thin layer of crema or pale crema that dissipates too quickly. Under-extraction occurs when the espresso has been brewed too quickly in the machine. In this case, 30 ml of espresso was delivered in less than 20 seconds. That is clearly not long enough. An espresso has been over-extracted if it tastes bitter, has a weak flavour and a thin dark brown crema that disperses quickly towards the edge of the cup. In this case, the extraction time was too long and 30 ml of espresso was delivered in more than 30 seconds producing over-extracted coffee.