Flow control - What is it & how to use it.

It’s big buzz in the coffee world at the moment. It seems like every man and their dog is talking about flow control (or maybe for me it’s like when you are looking at a new car and all of a sudden you seem to notice them everywhere on the road. Like did everyone just go out and buy the exact model of car I’m looking at? or was there always this many). I have recently fitted a flow controller on my E-61 machine, thanks to ECM for coming up with a needle valve and gage that I can retrofit to my Expobar machine ☺️.

Let’s quickly cover what flow control is. Flow profiling or flow control if you rather, is the ability and process of being able to control the rate at which the water flows from the group head. This can be used during pre-infusion and throughout the whole extraction (we will cover more about that later). Ramping up or ramping down the flow rate of water throughout the extraction at different points can have very different effects on the coffee, allowing baristas to have more control over the extraction.

I want to highlight one more thing before we delve into flow control and how it can be used. Flow profiling or control and pressure profiling are not the same thing, all be it they are related and can be used to try and achieve some similar outcomes. Pressure profiling aims to keep a set pressure (this pressure usually changes throughout the shot, ie. 3-4 bar at the start for a pre-infusion, then ramped to 9 bar for the end of the extraction ect). The machine will read pressure and increase the pumps power or reduce it to maintain the desired pressure. Where as flow control can have an effect on pressure, yet is not dictated by it. With flow control we are adjusting the millilitres per second (ml/s) whether or not pressure is being applied.

A simple way to use flow control, especially when starting out, is to use it at the beginning of the shot for pre-infusion. Starting at the beginning of your shot with a lower flow rate for around 5-10 seconds (3ml/s for light - med light roasts), (6ml/s for medium - medium dark roasts), then ramp up flow fairly quickly and finish extraction at desired yield. This method allows for an even, slow wetting of the coffee bed, allowing the coffee to bloom. This creates an even extraction, minimising the chance of channeling and also reduces acidity in the final cup (reducing acidity can be a good or bad thing depending on what you are trying to achieve. The important thing is knowing this and using it as a strength to manipulate the flavour profile when needed).

It is also good to know that infusing a coffee puck with a slow flow of 3ml/s, allows you to use a finer grind size than hitting it with a more traditional flow rate of around 9ml/s. This is especially true if you very gradually increase water flow and pressure, instead of a rapid increase from 3ml/s to 9ml/s. The reason

behind this is all to do with the smaller particles of coffee within the basket. When you apply a high flow of water into your coffee bed quickly, the flow and pressure move the small particles toward the bottom of the basket before they have time to swell up, causing a choking effect (for lack of a better term) slowing down your extraction towards the end of the shot. This means you need to keep the grind size courser to compensate. On the other hand when the flow rate is slower and more gentle in its ramp up, the coffee particles have time to swell and lock in place where they are originally distributed.

Another way of using flow control is to reduce the flow rate from the around 9ml/s to 6ml/s towards the end of the shot. This technique is to help alleviate channeling towards the end of the extraction. As water erodes away the coffee bed, channels can begin to open at the back end of the shot (no matter how hard we try to stop this, it is still a factor in extraction. I am more on the belief that all shots channel, you can never have perfect distribution, it’s just statistically improbable, what we are really aiming to do with a espresso extraction is keeping it to a minimum with no obvious large channels). Reducing flow rate at this stage allows coffee particles to settle back in to the potential channel, closing it up for the remainder of the shot.

Something I am a big fan of with flow control is the ability to increase water contact time and grind finer so that you can extract denser light roast coffees. These types of coffees can often be very hard to extract as espresso, the water just wants to flow through too fast. In turn, under extracting the coffee, resulting in a thin sour cup. This longer contact time coupled with a finer grind can highlight these sharper fruit flavours and acids while still allowing a balanced extraction, opening up the opportunity to taste the coffee in a way out of reach with more conventional styles of espresso brewing.

Using a combination of the pre-infusion technique, quickly ramping up to full flow and then backing off slightly at the end can produce are really amazing shot of coffee. Well rounded, balanced with a smooth body. This technique works best with light to medium roasted coffee.

For darker roast profiles, start the espresso with full flow rate at the start then ramp down the second half of the shot to reduce bitterness while keeping the more favourable characteristics of dark roasts. (I tend to mainly work with light and medium roast coffee’s, this is something I have only explored lightly with some quick testing and research).

Flow control has a lot of people in the coffee world really excited. People are hoping to find new exciting ways to brew with this, I don’t think this is where it will lead (although there is a cool theory I came across a while ago that I want to try, using a courser filter grind and a consistent low flow rate to produce a filter like coffee), I think what it will do is increase our ability to extract an even tasty coffee and increase our TDS without necessarily over extracting the coffee.

I do have some concern with bringing in another variable to coffee. My approach is always about aiming to brew consistent coffee to an agreed standard instead of aiming for one perfect shot in between 5 average ones. The best way to do this is to keep the processes used for making coffee, simple, straightforward and as minimum as required to brew coffee to your accepted and agreed standard. For this reason in a fast paced coffee setting ie. commercial volume, I do not think it is best practice to use variable flow control, unless it is a machine with set parameters that can easily be replicated without constant adjusting and attention from the barista.

At least for now, I think this process is more for slow coffee situations where you can take the time and care that is needed to get the most out of it and enjoy the whole process.

Happy experimental brewing,

Lars 😎☕️