How does an espresso machine work across nine extraction variables?

Consistent espresso comes down to controlling nine variables: water pressure, boiler pressure, water temperature, tamping force, grind size, dose, extraction time, extraction yield and crema. Modern machines typically brew near 92°C, while the first commercial models ran far hotter and at lower pressure, which is why old recipes do not transfer directly.

The article traces machine evolution from the 1901 Bezzara patent with multiple brewing heads to the 1905 Ideale, then moves to modern semi-automatic equipment. A working example uses 20 g of coffee to produce 40 ml of espresso, with the classic Italian blend as the reference, so crema and balance stay repeatable shot to shot.

Espresso may seem simple, but it hides many variables and depths of knowledge. From the perspective of Front Street Coffee, this article reviews the evolution of espresso machines from the first generation in 1901 to modern semi-automatic equipment, and provides a detailed breakdown of the nine major influencing factors: water pressure, boiler pressure, water temperature, tamping force, grind size, dose, extraction time, extraction yield, and crema. At the same time, using the classic Italian blend as an example, it gives specific operating steps and parameter standards for extracting 40 ml of espresso from 20 g of coffee, helping coffee lovers understand how to consistently make a cup of Espresso with rich crema and balanced flavor.

For more specialty coffee knowledge, please follow: Front Street Coffee (Frontsteet Coffee)

Many people's first impression of espresso is that it is heavily bitter and noticeably astringent, but in fact these problems often arise during preparation. Enthusiasts often ask Front Street Coffee, isn't making a shot of espresso something anyone can do? Indeed, the actions themselves are not complicated, but to consistently achieve a satisfying result, there are quite a few variables involved. Below, Front Street Coffee will talk with everyone about what exactly goes into extracting a shot of espresso.

First-Generation Espresso Machines The European Industrial Revolution brought a wave of technological innovation, and machine-made first-generation espresso appeared around 1901. The original starting point for designing espresso machines was very simple: to allow coffee to be made quickly.

Milanese inventor Luigi Bezzara patented a machine equipped with multiple independent brewing heads, allowing portafilters filled with coffee grounds to be attached one by one. This was the first time humans used a machine to quickly serve coffee to customers. In 1905, Desidero Pavoni bought the patent and put the first commercial espresso machine into production: Ideale.

According to materials reviewed by Front Street Coffee, the parameters of the first commercial espresso machine were very different from today's common equipment. Its brewing head temperature was as high as 140°C, pressure was 7.5 bar, and extraction time was about 45 seconds.

Here, Front Street needs to add a note on how modern espresso machines work: hot water at 92 degrees Celsius passes through a finely ground bed of coffee under 9 bar of high pressure, thereby extracting the coffee. The beautiful layer of crema on the surface of espresso is precisely the product of 9 bar pressure. Yet the world's first commercial espresso machine had only 7.5 bar of pressure, which means that the espresso of that time was closer in strength and taste to today's drip coffee.

With the appearance and spread of the new machines, the word "espresso" was added to Italian dictionaries around 1920. The definition given by the dictionary was "coffee made with a pressure machine or filter, now very common."

Modern Espresso Machines In the 1930s and 1940s, Italian coffee consumption declined, but technical improvements to espresso machines did not stop. In 1947, the manual pressure espresso machine was born, extracting more oils and colloidal substances from the coffee grounds, and crema has since become the soul of espresso. In 1961, the Faema E61 espresso machine was launched. The Faema E61 was the world's first semi-automatic machine and is also regarded as the father of modern espresso.

After discussing the history, next Front Street will demonstrate how to make a shot of espresso, using Front Street's classic Italian blend for extraction. This recipe is composed of beans from three origins: Brazil, Indonesia, and Vietnam. It uses a dark roast, which can maximize the coffee's rich aroma and also makes it easy to extract abundant, dense crema. Whether making an Americano diluted with water or a latte paired with milk, it is very suitable.

Front Street uses the Lelite V3 espresso machine: Temperature: 90.5~96 degrees Celsius Time: 25~33 seconds Coffee-to-water ratio: 1:1.7~1:2 Dose: 20 g Extracted espresso yield: 20 ml (single) 40 ml (double)

Step one, turn on the grinder and let the coffee grounds fall into the portafilter basket. The dose is determined by the capacity of the basket. For example, if Front Street uses filling 20 grams of coffee grounds as the standard, then each extraction should maintain 20 grams of coffee grounds (accurate to 0.1 grams).

Step two, distribute the grounds. After the coffee is ground, this is the process of manually placing it into the portafilter basket and distributing it evenly. The purpose of distribution is to spread the coffee evenly across the entire basket before tamping, so that not only is the surface level, but the interior and edges of the basket are also even with no gaps.

Step three, lock the portafilter basket into place, then begin extraction.

Doesn't it look simple? Not so fast, there is a great deal of knowledge behind it. There are nine factors that can affect the taste of a cup of espresso.

[Water Pressure]

Front Street Coffee has always talked about the principle of extracting a cup of espresso. The ideal water pressure for Espresso is generally around 9 BAR, and this is also the most ideal pressure widely recognized.

[Boiler Pressure]

Boiler pressure is related to the water temperature for making coffee and the force of the steam. The higher the boiler pressure, the higher the water temperature and the greater the force of the steam; conversely, the lower the water temperature and the weaker the steam. Boiler pressure is generally around 1 BAR. Of course, there is still much debate about this value, and every barista understands it differently.

[Water Temperature]

The water temperature needs to be determined according to the requirements of different coffee bean varieties. Some are constrained by boiler pressure, while others can be set more flexibly and precisely. According to the experience of most baristas, the water temperature is between 90 and 92 degrees Celsius. Every barista can adjust flexibly according to their own understanding and needs, and can make their own style of Espresso with their own hands.

[Tamping Force]

There are various styles of tamping, and in this world almost no two people tamp exactly the same way. Generally speaking, if it is a heavy tamp, the required pressure would be something like 25 kg/m2, but tamping is indeed the most freely chosen parameter among the golden rules. Because we use a calibrated tamper, the tamping force is basically consistent.

[Coffee Bean Grind Size]

Grind size is related to many factors such as climate, coffee bean roast level, freshness, humidity, and the age of the grinder. There is a saying long circulated in the industry: "The correct thing is that the grind size is always changing; the wrong thing is keeping the grind unchanged."

[Dose]

The reasonable capacity of Front Street Coffee's portafilter basket size is 20 grams. If the dose is too small, the extraction time is too short, which easily causes under-extraction; if the dose is too large, besides possibly not fitting, even if it does fit, the basket volume is only so large. After the coffee is tamped, the gaps between particles are reduced, the flow rate slows down, and the extraction time becomes too long, leading to over-extraction.

[Extraction Time]

The extraction time in the golden rules is set at 25~28 seconds, but extraction time is actually the combined expression of tamping, dose, and grind size, and needs to be adjusted by the barista based on their understanding.

[Extraction Yield]

Taking Front Street Coffee's espresso extraction as an example, 20 grams of coffee grounds extract 40 grams of espresso liquid, for a coffee-to-liquid ratio of 1:2. The ratio is not absolute and specifically depends on the desired flavor. If more coffee liquid is extracted, the coffee will appear thinner and the bitterness more obvious. If less coffee liquid is extracted, the coffee will appear viscous, rich, with more concentrated flavor but incomplete.

[Crema]

The complexity of coffee crema cannot be explained in just a few words. Simply put, a good Espresso needs rich crema that is golden with a brownish tint. Front Street believes that Crema has an irreplaceable place in a cup of espresso. As a symbol, it marks the characteristics of a cup of espresso, and the appearance of the Crema in a good-tasting espresso is also one judging factor. The state of the crema also tells the barista how the extraction of this cup turned out. For example, beans, freshness, roast level, and grind size will all produce crema in different states.

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