Weight Of The Tamper To apply the right amount of pressure your tamper needs to weight around 1-2 pounds. Avoid tampers made of plastic and opt for one made with heavy material such as stainless steel. According to professional baristas, tampers around 1 pound seem to be the best.
Espresso is normally extracted using nine bar of pressure, delivered via the pump connected with the machine. This is equal to approximately 60 kgs of force per inch2.
One of the most important is the pressure applied to the grounds, which should be somewhere between 8 – 10 kg. Too little pressure and the espresso will be under-extracted and weak, while too much pressure can result in a bitter and overextracted espresso.
Tamping pressure shouldn't be too hard as it can lead to over-extracting and an extremely bitter taste of espresso. Polish the puck with a twisting motion. Avoid twisting as you push down though. Otherwise, you can ruin the packed coffee.
Apply 20-30 pounds of pressure, and polish
Baristas often recommend 30 pounds of pressure, but some do as little as 20 pounds. More and more are finding that tamping pressure is overrated—it's hard on the wrist and cause an over-extracted, bitter brew. Use a twisting motion as you pull up to “polish” the puck.
Some say, you need to tamp very hard, others say pressure really is not important. According to experts, tamp pressure is not that important, what is important is ensuring that the tamp pressure is consistent each time and that your tamping is flat and as level as possible. This ensures you have the best results.
Pressurized portafilters (generally) do not need tamping down. Brush the edges of the filter basket off so there are no stray coffee grounds to get into the threads of the brew head. I like to smooth the basket down with a light tamp to make sure the grounds are even within the basket.
Common reasons for a wet espresso puck include; too little espresso in the portafilter, wrong grind size, uneven distribution of grounds, and air pockets due to improper tamping.
Tamping wet soil or clay is not an effective way to compact it. Oftentimes, this will only lead to the material sticking to the tamper. To prep wet dirt for tamping, rake it out as much as possible and give it ample time to dry. Don't let it over-dry, though: Completely dry dirt will not compact well.
You don't necessarily need to wet gravel before compacting, however a light amount of water can help to keep dust levels down. Just be sure not to make the area too wet.
In short, we found that higher tamping pressure made no difference to the extraction. The extraction times weren't longer for the 30kg tamping, nor were they more consistent from shot to shot – they were exactly the same.
Tamper Size Standards
A 58mm tamper is often used with commercial and high-end espresso machines (espresso coffee makers), while smaller size options include 57 mm, 53mm, and 49mm tampers.
The purpose of tamping is to create a resistance using the compacted coffee and making the water work to push through it. This is how the flavor is extracted. Learning proper espresso tamping – how the ground coffee is packed into the portafilter (basket) – is key to getting this right (1).
If the tamper isn't level during an espresso tamp, it can make the espresso uneven inside the portafilter. And the water will flow toward the side of the espresso that is less compressed. This will cause an imbalance of flavor, adding an over-brewed hint of bitterness.
Damage can occur if you overtighten the portafilter when locking it in place to brew, and wear occurs just by using the machine normally.
If your grind is too coarse, the water will flow too quickly through the grounds, producing a weak and watery shot. Solution - adjust your grind to the fine side slowly. Always make sure you're adjusting your grinder as it's in operation. Failing to do this can lead to jamming.
While the tamped espresso was sweet with punchy acidity and a persistent crema, the non-tamped espresso was woody, with a bitter finish and crema that dissipated almost instantly.
The ideal level of BAR passing through your coffee grounds should be around 7-11 BARs of pressure, though some espresso machines will be able to hit higher BAR. Machines capable of hitting 9 BARs of pressure will have the ability to produce a rich and concentrated espresso shot.
Unlike tea which can be reused for the next, less intense brew, coffee powder however cannot be used more than once. The first extraction is the only enjoyable brew. Consequent extractions make the brew bitter and devoid of the bold flavor of coffee.