Portafilter needs to be turned towards a point whereby it is snug and fit, NOT tight. There is not a need to push the portafilter towards to the extreme tightness all the way.
Too much coffee may be dosed into the portafilter.
If there is too much coffee in the portafilter, it can press into the shower screen and prevent the portafilter tightening all the way. Reduce the amount of coffee in the portafilter and try again.
As different portafilter baskets can hold varying amounts of coffee, you'll need to dose accurately depending on your basket size. If you underfill the basket and the puck sits too low, the water will flow around the top, rather than evenly through it.
Keeping the portafilter warm (and receiving / tamping a dose within a warm portafilter) is supposed to result in additional oils being released in the extraction, which in theory leads to a fuller pull and more crema. It's also supposed to add to the benefits of pre-infusion.
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.
Damage can occur if you overtighten the portafilter when locking it in place to brew, and wear occurs just by using the machine normally.
Portafilter needs to be turned towards a point whereby it is snug and fit, NOT tight. There is not a need to push the portafilter towards to the extreme tightness all the way.
Preheating: It is important that the cup you are extracting into is preheated as well as the portafilter handle otherwise they will suck the heat out of your coffee - destabilizing the temperature aspect. The coffee will be colder, potentially bitter and thoroughly unsatisfying.
If you tamp low-quality coffee grounds too hard, your espresso becomes over-extracted and thus extremely bitter. Besides pressing too hard or too light, a lot of beginning baristas tamp unevenly. While this mistake is underrated, it occurs frequently.
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.
Generally, darker-roasted coffees perform well with a smaller ratio, while lighter-roasted coffees perform better with a larger one. Borrowing language from Italian espresso nomenclature, a 1:1 to a 1:2 is a Ristretto espresso, 1:2 to a 1:3 is a Normale espresso, and a 1:3 to a 1:4 is a Lungo espresso.
If your coffee puck is too soft or muddy, then you are dosing too low (Picture #3). A low dose means that you may have had channelling through your coffee, causing an uneven extraction (see the holes in Picture #3). Also, your espresso will lack body and sweetness, making it taste a little thin and over extracted.
Having wet and soggy puck means that the pressure is off on one or more elements, causing excess water to be left in the portafilter.
2. Overfilling Filter Basket. Filling the portafilter with too much espresso during an espresso tamp creates uneven extraction from the grounds, and filling it with not enough espresso creates uneven extraction as well. Too much grounds results in a stronger and over-brewed coffee.
You can leave it on the machine but I recommend if you do that taking the portafilter off and wiping it dry prior to putting coffee in there because you really want a dry portafilter for the best tamping results.
Is A Bigger Portafilter Better? A bigger portafilter does not necessarily mean it is better. The size of the portafilter depends on the espresso machine and the type of coffee being brewed. Some espresso machines require a specific size of portafilter to work properly.
Tamp twice. For the first tamp, apply a light amount of pressure to form a puck shape and for the second use give it a bit more force and press heavily down to remove any obvious spaces between the grinds.
The water sprays through the grounds, making something weak and unpleasant-tasting. On the flipside, tamping too hard leads to the opposite happening. Water struggles to get through the puck, and because it spends more time seeping through, your espresso becomes over-extracted.
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.
That's why you should always aim to let your espresso extract for 25 – 30 seconds. The perfect extraction time for an espresso is 25 – 30 seconds. This is true for pressurised and non-pressurised baskets.
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.
Dirty portafilters and baskets can also cause coffee to taste ashy and bitter if not cleaned properly. You should regularly clean these parts during service. Give them a good soak in hot soapy water at the end of the day, before scrubbing, rinsing and putting back into the machine.