What is a coffee tamper and what does it do?
A coffee tamper is used to compress ground coffee in the process of making espresso coffee
Why is it necessary?
As a rule of thumb, you should be aiming to brew about 30mls of espresso in 25 seconds (from a single coffee basket) to get 'good espresso', and to do this you need to get several factors right all at the same time. Espresso machines produce very high pressure water (typically between 900 - 1500kpa, or 9-15 bar) which is required to properly extract the flavour from the ground coffee, and with no restriction a 15bar pump will flow much more than this amount of water. Therefore, the ground coffee must present a significant amount of resistance to the water flow to reach the above figure. To achieve this,
- the coffee beans must be ground to the correct size, and
- the ground coffee must be compressed tightly with a coffee tamper
Imagine you want to pour a bucket of water into a metal sieve but you only want a slow trickle of water to come out the other side. If the sieve contains large pebbles, the water will just run straight through (which correlates to having the coffee ground too coarse). Nothing you can do to the pebbles will significantly slow the flow. A similar result might occur if the sieve was full of loose flour. However, if you packed that flour into the sieve very tightly (which correlates to correctly ground and tamped coffee), the water would take a lot longer to get through, and this is the purpose of a coffee tamper - it compresses the ground coffee to increase the water resistance, and doing this helps achieve optimum extraction of the coffee.
What is the single most important thing to look for?
With the above information, it should be clear that the coffee needs to be compressed evenly. Imagine if you only packed down half the sieve of flour? The water would pick the path of least resistance and just run through the loose part. In coffee terms, this means the loose part would be 'overextracted', which tastes very bitter, and the packed part would be 'underextracted', or barely touched by the water. Therefore, probably the single most important factor is that, to pack the coffee down evenly, the coffee tamper needs to be the right size for your filter basket. If the tamper is too big, it won't fit your filter basket; if it's too small, it will only tamp some of the coffee and you'll need to tamp several times. It's normally impossible to exactly repeat a multi-tamp process, so an undersized tamper should be avoided. A correctly sized tamper will compress all the coffee in a single tamp, and leave no untamped coffee around the edges of the basket.
There are many different sizes on the market and the correct size tamper depends on your machine. Your machine manufacturer should be able to tell you what size you need, although this will only be an approximate figure. Your coffee tamper supplier may be able to help, and at least one reputable coffee tamper supplier in Australia will actually offer to measure your filter baskets to ensure you get the right size tamper. This really is the only way to get the right size tamper for your machine.
What sorts of tampers are on the market?Most tampers are hand-operated, as the one shown in the picture, where you use manual force to compress the coffee. However there are also machine-mounted or grinder-mounted tampers. These don't take any extra bench space so may be good when space is very tight, but they require a lot more force as tamping upwards is against gravity and is an unnatural motion for most people. There are also some mechanical tampers which resemble a small drill press. As hand tampers are the most common, this guide looks mainly at this type.
There are tampers on the market made from plastic, aluminium, stainless steel, brass, copper, wood, and a mixture of these materials. As you can imagine, prices vary significantly depending on what they're made from and the build quality of the unit. So long as it's the right size, any of these will do the job, though some will do it much better than others. Which is best for you depends on your personal style preferences, how much you're prepared to spend and how comfortable you want it to be during use. A good tamper will fit correctly, look the part, be comfortable to use and last for many years, whereas a cheap one may be uncomfortable, look ugly and only last a couple of years. The choice is yours depending on what's important to you.
Another difference is that some tampers have flat bases and some have curved bases. There are many discussions on the internet about which is better - to me a flat base will pack more evenly than a curved base, but I'll leave you to make up your own mind.
But my coffee machine came with a coffee tamper - do I need another one?
Most coffee machines will come with a tamper, but it's often very loose, which means you have to tamp many times, or tamp in an 'around the clock' motion to compress all the coffee. Both these methods lead to unrepeatable results. If your tamper has hardly any wobble when it's in the filter basket, chances are you don't need to replace it, although you may feel a cheap black plastic tamper doesn't match your expensive espresso machine. However if your tamper has a lot of wobble in it, you would definitely notice an improvement with a correctly sized tamper.