Our head barista trainer Jackson writes about how to tamp coffee properly. What is it? Why is it important and what are your options?
Tamping is often viewed as one of those mythical rituals that you see your barista performing on the other side of the counter. A shrug of your baristas shoulders as they appear to lean on a tool that is clearly doing something to your freshly ground coffee before it is clicked into place in the coffee machine. But what is really happening here and as a barista, what do you need to know about how to tamp coffee properly?
First of all, what are you trying to achieve?
Knowing how to tamp coffee properly is important because producing good espresso coffee is all about achieving the perfect extraction and producing good espresso coffee all the time is about achieving perfect extraction consistently. Tamping coffee properly is all about consistency and evenness of extraction. By tamping, you are trying to create an even ‘bed’ of coffee that, when inserted into your commercial coffee machine, will allow water to pass through it evenly.
For water to pass through evenly, at pressures of up to 9bar, the coffee bed must be perfectly flat, and without any cracks or discrepancies of density. Water at this kind of pressure will exploit any fault in a coffee bed and will pass through the path of least resistance. This will cause areas of your coffee to be over-extracted and other parts to be under-extracted leading to a poor-quality coffee.
Problems of unevenness
An uneven bed will mean that the majority of water will be forced through the thinnest part of the coffee bed. This means that all the time and effort spent perfecting the perfect brew ratio will be out the window as now, a small percentage of your coffee will be exposed to a high percentage of your water.
As shown by the diagram, water is applied evenly to the coffee bed but more water passes through the shallower section of the bed, over extracting this coffee and under extracting the rest.
Problems of cracking
Cracking’ refers to weaknesses in the coffee bed that, when exposed to pressurised water, become a channel for the water to pass through. Again, this will mean that your coffee is not exposed to the brewing water evenly and in extreme cases, some parts of the coffee will hardly be extracted at all.
As shown by the diagram, water is applied evenly to the coffee bed but travels through the crack in the coffee bed and so most of the water travels through this part of the coffee bed and the rest of the coffee is under-extracted.
Problems of uneven density
Even if your bed of coffee appears perfectly flat, if one side is more densely compacted than the other, the same issues of unevenness apply. This can occur when the coffee has not been evenly spread out before tamping.
As shown by the diagram, water is applied evenly to the coffee bed but more water passes through the less densely packed section of the bed, over extracting this coffee and under extracting the rest.
How to tamp coffee properly and consistently
Consistency starts with the grinder, you need one that is able to produce an even grind at a fineness appropriate for espresso extraction (to see the Caffeine Limited range of grinders, click here).
To achieve the perfect extraction, your coffee must be level, and evenly distributed without any cracking or channelling.
Once your coffee has been ground into your portafilter, the first stage of tamping requires you to roughly level out the coffee grounds. I do this by lightly shaking the portafilter, others use a finger to distribute the grounds. It is important not to compact the coffee at this stage if distributing with a finger, and it is important not to knock or shake the grounds too much as this will cause the larger grinds to gather together (Never knock the portafilter with the tamper!)
Next, resting your portafilter on your tamping matt, rest the tamper on top of the ground coffee (it is important to use the right size tamper for your portafilter! It should fit snuggly inside it). visually check that the tamper is level and adjust if not. Gently spin the tamper over the coffee to smooth the surface before applying some pressure directly down through the tamping handle. Try to ensure that this pressure is applied evenly.
The optimum pressure needed for tamping is often debated but I have found that the pressure needed to adequately compact the coffee is between 4kg and 5kg, but this doesn’t mean much without practising on a scale. I often describe the pressure to my trainees as firm but you should be able to recreate the pressure on the back of my hand without worrying about hurting me.
The Final Touch (or lack thereof)
Once you have applied your pressure evenly and have created a flat bed of compacted coffee, do not tamp again! This may cause cracking and therefore channelling. Equally, take care not to knock your portafilter against the coffee machine as this can have the same effect. Instead, wipe and coffee grounds from the edge of the basket and insert into your coffee machine for the perfect extraction!
If you are worried about the complexity of producing quality coffee on a barista coffee machine, you should consider a Schaerer Bean to Cup machine from Caffeine Limited. You can see our entire range by clicking here. The Schaerer Barista in particular, retains the drama and theatre of barista coffee preparation but doses and tamps the coffee automatically, ensuring quality every time.