How is Espresso Brewed?

By Coffeenated Stories | 9 min read

Updated On: NOV 18 2023

Disclaimer: CoffeenatedStories.com is a member of the Amazon Associates Program, and as an Amazon Associate, we earn from qualifying purchases.

Initially invented in Italy, espresso is a small and intense cup of coffee brewed under pressure. The coffee yielded with this method is dark black and syrupy with a lovely crema on top. Over the years, espresso has become one of the most popular ways to drink and brew coffee from roasted and grounded coffee beans.

In the process of making espresso, hot water, under pressure, typically between 6 to 9 bars, flows through a basket of 7 g of ground coffee that is nicely compacted or tamped for about 25 to 30 seconds to produce about 25 g of espresso or a single shot of espresso.

The data in the table below shows the most important technical parameters of a Certified Italian Espresso, published by the Italian Espresso Institute.

Technical Parameters to make a Certified Italian Espresso
Necessary portion of ground coffee7 g ± 0,5
Exit temperature of water from the unit88°C ± 2°C / 190° F
Temperature of the drink in the cup67°C ± 3°C / 152° F
Entry water pressure9 bar ± 1
Percolation time25 seconds ± 5 seconds
Viscosity at 45°C> 1,5 mPa s
Total fat> 2 mg/ml
Caffeine< 100 mg/cup
Milliliters or grams in the cup 25 ± 2,5

Often you will see recipes calling for a larger dose of ground coffee, maybe something like 14, 18, or 20 g of ground coffee. That is because they are brewing inside a double basket.

Today, many modern coffee shops serve double espresso as their standard, and many traditional coffee shops serve single espresso. When making espresso, regardless of a single or double espresso shot, you often need to measure some parameters and establish ratios.

Espresso Ratio

The most apparent ratio in making espresso is the weight of ground coffee on one side compared to the grams (g) or milliliters (ml) of brewed espresso. For example, brewing a shot with 15 g of ground coffee and yielding 30 g of espresso is a 1:2 ratio.

Changing this ratio will produce a different type of espresso. The "ratio" is a beneficial way of thinking and brewing coffee, especially espresso. It would be best to keep in mind that the more yield we make from a fixed amount of ground coffee, the weaker that drink will be.

When passing through the ground coffee, hot water dissolves the soluble materials from the coffee. That is essentially what happens when brewing. The more water we use, the more extraction we'll get, but we'll decrease the strength of the coffee. If we do that, when making espresso, we will lose the espresso's texture, body, and richness.

In terms of proportion, the weight of ground coffee to yield espresso, there are three main types of espresso:

  • Ristretto, meaning restricted or short espresso, is a coffee drink with a ratio of 1:1 or 1:1.5 ground coffee to yield liquid. Ristretto will be an overwhelmingly intense drink with estimated dissolved solids brewed from the coffee at around 13% or 14%, with the rest of the cup being water.
  • Espresso typically is made with a ratio of 1:1.5 to 1:2.5. Increase the yield to make an espresso, and you'll get more texture and tones of flavor in your cup with about 10% dissolved solids in the cup when brewed rightly.
  • Lungo, meaning long espresso, is made with a ratio of 1:2.5 to 1:4. Lungo contains 6% to 8% dissolved solids from the coffee in strength, and with Lungo, we will get a more balanced but less textured experience than espresso.

Espresso Ratios
Espresso Ratio
CoffeenatedStories.com Archive

When ordering or brewing these drinks, we need to remember that it is all about personal preference and choice. None of the three drinks is necessarily better than the other.

These ratio values are not definitive or final on how we should make espresso. There are here just for guidance and to provide us with some definition of what espresso and its variations are.

Espresso ratios are just abstract ideas of what espresso is. We consider these ratios only as a starting point at the beginning of brewing our espresso.

After brewing the first espresso with any of these ratios, we'll have to make adjustments and tweaks to our grinder and maybe the water temperature.

Start considering the roast level, the origin, the altitude of the place where the coffee has grown, the size and quality of the basket in your machine, and the espresso machine itself.

In some cases, we might consider lowering the dose of ground coffee in the basket. Typically with high-altitude grown, lightly roasted beans, we want to brew a slightly lower amount.

Espresso Grind Size

When making coffee with any method, the grind of our coffee is essential. The size of ground coffee particles has a massive impact on the coffee you are brewing.

With espresso, even the tiniest changes in the grind size will directly affect the shot. In some cases, it might be the most critical change to move from a good to a great cup of espresso.

The grinder is arguably essential in the espresso brewing process and is also the most frustrating part for many reasons.

Coffee Grinder
Coffee Grinder
Nguyen Tong Hai Van by Unsplash - https://unsplash.com/photos/pkj935eY62A

When we put finely but inconsistently ground coffee in the basket, the harder it is for water to flow evenly through the coffee. Many of today's coffee grinders are not perfect. Namely, because they don't output the same amount of coffee we put inside them, they retain some of the coffee it grinds.

When we change the grinding step, the new coffee will push the retained coffee from the previous grind into the newly ground coffee, mixing the two different grounds. And we will end up with inconsistently ground coffee in the basket.

So whenever we change our ground setting, we need to purge some coffee until the coffee grounded with the new set comes through, which is frustrating because we will waste the purged coffee.

The finer our coffee grounds are, the more surface area we'll expose, and when tamped, the grounds fit more inside the basket, which will make it more difficult for water to flow through them.

So this one change will decrease our flow rate and increase the pressure and the contact time between the water and the coffee.

When the pressure rises inside the basket, from 6 to 9 bars, water might find a channel to run unevenly through the puck. When brewing finner grounds, the pressure build-up in the basket will break the puck and create a channeling.

Channeling in Espresso Brewing

Channeling means more water will pass through one area, essentially over-extracting the coffee there. And not enough water will pass through another part of the basket, resulting in the under-extraction of that area. The result of that will not be a delightful cup of espresso.

So what we need to do is grind the beans fine enough to expose a fair amount of surface area. Evenly distribute them across the basket, tamp them down enough to extract all the goodness from the coffee, and have water flow evenly through the basket without breaking the puck and creating channeling. Please read our article to learn more about what causes channeling in espresso.

A good grinder will help you by grounding your coffee into even particles and making the water flow through the basket even when brewing. The best grinders for this job are burr grinders.

Best value
Fellow Opus

Fellow Opus

The Fellow Opus electric burr grinder is an excellent entry-level option.

Premium Choice
Comandante C40 MK4

Comandante C40 MK4

The Comandante C40 MK4 is a high-quality hand coffee grinder that sets new standards among premium hand mills for coffee.

Besides good grinds to achieve even extraction, a technique called preinfusion we can use before the brewing process starts.

Preinfusion in Espresso Brewing

Preinfusion is when a small amount of water goes slowly into your coffee grinds and soaks them before we begin brewing our shot of espresso. The water saturates the coffee and makes it swell and even out in the basket.

When brewing espresso, it would be best if we had preinfusion because when we hit the puck of dry coffee with 9 bars of pressure, it is very likely that some water will go squirting through some parts of the puck and create channels.

Without preinfusion, making a dry coffee puck that is even and can withstand 9 bars of pressure without creating channeling is hard.

So, preinfusion is a technique that many modern espresso machines use to prepare the puck of coffee in the basket.

After preinfusion, when the brewing starts, the pressure gently rises and compresses the coffee puck, and we'll get a much more even extraction from the coffee. And even if channeling does acquire, it will happen at a later stage of the brewing process and will not impact the espresso considerably.

Water Temperature in Espresso Brewing

Next to coffee beans, water is the other half of your espresso. Besides using clean and fresh water, we should consider the temperature of the water when brewing espresso.

Generally, the higher the water temperature is, the more extraction will make from the coffee. So, the lighter the roast of the coffee beans is, we should use higher-temperature water to brew our espresso.

Using high-temperature water with a darker roast would not necessarily ruin our shot, but in some cases, we might have over-extracted espresso in our cup.

Changing the water temperature should be done to make minor tweaks or improvements when brewing some types of roasts of coffee and make them taste great in the cup.

Water Pressure in Brewing Espresso

When brewing espresso, we are trying to run a small amount of water through a finely ground and compact basket of coffee. So, to do that, we need some pressure on the water.

Typically, most espresso machines will have a water pump to force the water through the coffee with a pressure of 9 bars or more.

Using pressure higher than 9 bars compresses the coffee in the basket, and the water flow slows down. Too finely ground coffee may even stop the water flow through the puck, which is not the effect we want to achieve when brewing espresso.

On the contrary, low pressure will not make the water flow through the coffee. So the brewing pressure of 6 to 9 bars is considered an industry standard and is a sweet spot for most espresso machines.

Espresso Baskets

Inside the basket, the grounded coffee and the tamping causes the majority of the resistance to the water flow. But also, the basket itself plays a role in that it too resists the water and decreases the flow rate.

The espresso basket is a predominantly solid surface with tiny holes punched through its bottom. That resistance and flow rate restriction coming from the basket should not be the same for every dose of coffee.

For example, we would not want the same resistance for brewing 16 g and 20 g of coffee. Because if we have the same resistance for brewing 20 g of coffee, we would need to grind the coffee coarser to have the same flow rate as if brewing with 16g of coffee.

Seeing that, the manufacturers of baskets create different baskets for various doses of coffee. The differences in the baskets are mainly in their height and the number and size of the holes.

What we typically see on the side of the basket is the printed dosage for that basket. We should respect the recommended dosage of a basket in terms of not overdosing on a basket, but underdosing a basket is perfectly fine.

There will be more space between the coffee puck and the group head if we underdose a basket. When the pressure drops at the end of the brewing, the puck will expand in that space, and we will end up with a runny, soupy coffee puck.

We can find pre-ground coffee recommended for brewing espresso in the Super Markets worldwide. The pre-grounded coffee is usually grounded too coarse to brew coffee with these baskets.

So manufacturers have made a so-called pressurized basket. Pressurized baskets on the inside are the same as non-pressurized baskets, but there is only one tiny hole for espresso to come out on the outside. That is to increase the pressure in the basket when brewing the coarsely pre-grounded coffee.