![]() In doing so, any micro-cracks and holes in the puck are sealed. The coffee grounds press against each other, and against the walls of the portafilter. When this happens, the puck absorbs the water and expands. We now know that during pre-infusion, the coffee puck in the portafilter is evenly soaked with water. After all, when a barista pumps out 300+ espressos a day, fatigue and strain is bound to set in occasionally. Even professional baristas can slip up during tamping. ![]() This isn’t just something that affects rookie baristas. In short, it will taste absolutely terrible. The result is an unevenly extracted espresso. What happens if this occurs? The coffee around the channel that the water flows through will get over-extracted, whilst the rest of the bed will be under-extracted. Or, if your coffee puck is thicker on the left side, the water will flow through the right half. So if there is a weak spot in the coffee puck, such as a crack, the high-pressured water will punch a hole in it and flow out through that channel. It will always take the path of least resistance. If the full 9 bars of water pressure directly hits a coffee puck with these issues, a phenomenon called “channeling” will occur.Ĭhanneling is when high-pressured water finds a path of least resistance in the coffee puck to flow through, instead of evenly passing through the entire area. Or, if you’ve tamped unevenly, there could be a spot in the puck that’s less dense than the surrounding areas. The concept of pre-infusion was to help mitigate problems that could occur whilst tamping.įor example, if you’ve failed to properly collapse and distribute your coffee grounds, there could be cracks or air pockets in the coffee puck. The first drops of liquid espresso start falling into your cup.īut why do we need it? What’s the purpose of pre-infusion? Why Do We Need Pre-Infusion? The high-pressured water then starts the actual extraction of the espresso. Then, after the coffee puck is fully saturated with water, we hit that 9 bars just like before. ![]() This is what we call the pre-infusion stage. This water flows into the portafilter and soaks the bed of ground coffee until it is completely wet. More often than not, it’s just your normal, everyday tap water pressure. This can be anywhere from 1-5 bars of pressure. When you push start, low pressure water is first allowed to gently flow in. Now, with pre-infusion, it’ll look like this: If you brew your espresso for 30 seconds, the pump forces the water out at 9 bars for the full 30 seconds. This version has been super-simplified, but as you can see, the 9 bars of pressure are at a constant. It’s called a pressure profile graph, which shows you how the water pressure changes according to time. You might have seen a graph like this before. ![]() Traditionally, the 9 bars of water pressure is maintained throughout the entire extraction time – from the moment you push start, the pump activates, until the last drop of espresso drips into your cup. To achieve this, an espresso machine utilizes a powerful pump to build up that immense pressure to force it through the coffee puck. Don’t fret – I’ll explain.įor normal espresso extraction, 9 bars of water pressure (130 psi) is required. If that sounds complicated, that’s because it is (sort of). This minimizes channeling, promotes a more even extraction and achieves a better tasting espresso. Pre-infusion is the initial process of using low-pressure water to gently wet and expand the coffee puck in the portafilter, before using the full 9 bars of pressure for espresso extraction.
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