Have you ever struggled to keep your espresso extraction time consistent? Perhaps you’ve checked the machine to confirm the pressure and temperature are steady. You’re dosing correctly. And you’re careful to tamp well. But no matter how closely you follow these best practices, your extraction time keeps varying.
So, what’s the problem?
Well, it could be your flow consistency. One of espresso’s most overlooked variables, flow rate can affect consistency and even be used to better control extraction.
To learn more, I spoke to two Dalla Corte Coffee Pros: Danilo Lodi, a World Barista Championship judge from Brazil, and Simone Guidi, who is an Authorized SCA Trainer (AST) and coffee roaster in Italy.
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Pulling an espresso shot on the Dalla Corte Mina. Credit: Dalla Corte
What Is Flow Rate?
Let’s start by defining flow rate: it’s simply the amount of water flowing out of your group head over the amount of time in which the pump is activated.
In other words, it measures how quickly or slowly the water flows during espresso-making.
And if you don’t have a consistent water flow, not only will the extraction time vary but the espresso flavor profile will do too. As Simone Guidi says: “If I give more or less water to the coffee, it releases more, less, or in a different way, the aroma.”
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Which means that even just one group with an inconsistent or randomly varying water flow can cause significant problems.
Shot of espresso. Credit: Jeremy Ricketts
When Flow Rate Is Inconsistent, Everything Goes Wrong
So, what happens if your flow rate is inconsistent? Danilo gives me this example: “You’ve set up your grinder in your coffee [shop] for a specific amount of time and weight, so you want your extraction, for example, to be 20 grams in/38 grams out in around 20 seconds. Let’s say that one of your groups has a lower flow than the other, or in your fifth extraction after you do that, you have a higher flow.”
Here’s what will happen:
With a lower rate: “You’re going to increase the amount of time that the coffee and the water will be in contact and you will decrease the pressure inside the portafilter, forget about the pump pressure, but the resistant pressure inside the portafilter chamber.”
With a higher rate: “You will decrease the [extraction]… plus the pressure on the portafilter chamber will change.”
In each case, the altered contact time and pressure affect the flavor and quality of the espresso. This negates all the hard work you put into dialling in and finding the best recipe, and also leads to inconsistent coffees – something your regulars will notice.
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Coffee Beans, espresso, and espresso based beverage. Credit: Nathan Dumlao
What Causes an Inconsistent Flow Rate?
There are many issues that can affect your flow consistency: pump malfunctions, worn-down parts that need replacing, or even old and outdated machines.
But it’s not just about your equipment. It’s also about how you’re using and maintaining it. Danilo tells me, “Especially on high-standard machines… it’s not a problem with the pump. Sometimes the users are not properly cleaning one group or are only using one group all the time.”
Remember, if you’re going to invest in high-quality equipment, you need to look after it.
The Dalla Corte XT Espresso Machine. Credit: Dalla Corte
Easy Ways to Calculate Your Flow Rate
Danilo recommends that everyone who has an espresso machine, either in a café or at home, calculates their flow rate. Do it at least twice for each group, without the portafilter.
“You put a precision scale at the bottom of the machine and a pitcher under the group head, and then you start the group pump and a timer at the same time, and you do it for 20 seconds…” he advises.
“After you’ve finished, let’s say you have 200g of water, so you know that you are extracting 10 grams/second. Because you went through 20 seconds and 200 grams.”
Espresso ready to be enjoyed. Credit: Jonas Jacobsson
Can a Varying Flow Rate Ever Lead to Better Espresso?
But keeping it consistent is only the start of using flow rate to produce better espresso. Yes, you want a controlled and repeatable rate – but that doesn’t mean it has to be the same throughout the extraction. And in fact, controlled variations in flow rate could allow you to pull even better, more delicious shots.
Simone uses the Dalla Corte Mina, a professional single group machine that allows you to alter the flow rate mid-extraction, following a profile you created beforehand. He says, “We found that, by changing the flow rate during a certain time or period during the extraction, we are able to make the coffee soluble in different ways. So [we can] extract in different ways the aromas from the coffee.”
He remembers going to World of Coffee 2017: Budapest and inviting roasters from all over the world to try their coffees, which he had brewed with different flow profiles. “It was funny,” he says, “because when I gave the cup to them they didn’t recognize it. They said, ‘This is not my coffee. It’s better!’”
Pulling an espresso shot from the Dalla Corte XT Espresso Machine. Credit: Dalla Corte
How to Manipulate Flow Rate for Better Espresso
So, what can you achieve by manipulating the flow rate? Simone says, “I can reduce the bitterness, I can reduce the acidity, I can reduce astringency, because sometimes that happens. I can reduce the dryness and I can improve the sweetness.”
Like all things coffee-related, there’s no simple recipe for flow rate. It always depends on the coffee in question. But Simone was willing to offer some guidelines for those beginning to play with this variable.
“We can’t give a general answer to this,” he stresses, “but I’ve seen from my personal experience that by being more gentle, which means a lower flow, at the beginning, you are more able to extract sweetness and the acidity is more complex. So, the cup becomes more balanced and more bright, [thanks to] being gentle during the pre-infusion.”
Using the Dalla Corte app to control the flow rate profile for an espresso shot. Credit: Dalla Corte
Flow rate: it’s espresso’s forgotten variable, but it can have a dramatic impact on quality and consistency. So, what are you waiting for? Go check the flow rate on your machine!
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Written by Ivan Petrich.
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