Consistent and High Quality Espresso Shots Depend on Proper Tamping
When people talk about brewing the perfect espresso shot they often describe in detail such things as the particular coffee roast and blend being used, how the coffee should be ground, the length of the espresso extraction time, and many other details.
However, often very little attention is paid to the tamping of the ground and roasted coffee even though the tamping is clearly a very integral and crucial part of the espresso brewing process. When the grounds are given a proper tamping, the espresso develops just the right consistency.
The skilled barista learns to apply just the right tamp, which may be adjusted given all of the other variables involved including the pressure, temperature, coffee type, grind size, and even climactic conditions. This is the artistry and panache of the espresso barista!
Proper Tamping Pressure
Expert baristas often prefer a tamping pressure of about thirty pounds of downward force, although the precise amount of force may vary given the other variables.
If the coffee has been properly roasted and ground for espresso, and the portafilter and demitasse are preheated, then thirty pounds should be about the perfect amount of tamping pressure to produce about three ounces of espresso (a double shot) in about 25 seconds.
What does a thirty-pounds-of-pressure tamp look or feel like you ask? Well, it will be a nice, tight puck, very well compacted.
What is channeling during an espresso pulling?
Channeling is what may occur when you don't tamp the coffee grounds, or when tamp with too little pressure, say less than about twenty pounds of downward force and the water finds its way through the less compacted areas of the coffee grounds much faster than it goes through the compacted areas.
Some Espresso Tamping Tips
First of all make sure you are using freshly ground coffee right from the grinder, preferably a conical burr grinder. Then grind about seven grams of coffee for a single espresso shot or 14 grams for a double shot. Err on the side of more rather than less.
Next overload the basket just slightly and tap the basket and portafilter a few times so the grinds settle a bit before leveling. It is important to level off the ground coffee so it fills the basket evenly and with a consistent density previous to tamping - this is crucial to creating a sound puck.
The tamper fits tightly into the basket and is used to compact the grounds before pulling the espresso shot.
The goal is to “seal” the puck so that the water, when forced through the grounds at a high temperature and pressure, moves through the grounds evenly. The hot water should not be able to find any weak spots where it will penetrate too fast and gush though.
If the hot water moves too swiftly through a weak spot it will be at the expense of the puck's denser areas which will be insufficiently extracted thus detracting from the overall quality of the espresso shot.
Some Tamping Tips
Try to tamp very straight down with an even pressure and then just give it a very light twist which will help to settle and stray coffee grinds.
Some baristas like to apply a slight rolling or nutating motion, which is similar to the motion a coin makes when it is settling after being flipped.
This motion helps ensure that the coffee grinds on the edges of the basket are well tamped. This is less necessary if you are using a convexly curved tamper.