The Coffee Tamper is one of the most important tools you will ever buy. It is used to compress coffee. When using ground coffee beans to make espresso.
For most commercial machines the best tamper to have when utilising a double filter basket is one which has a 58mm diameter and has a convex bottom.
Occupying most of the space at the top of the basket is a good idea when tamping.
A convex based tamper allows for a correction in compression. Explained in more detail on the tamper FAQ sat on the blog.
Looking at the side of a filter basket, in most cases, the sides slope in towards the bottom.
So a tamper with a 58mm flat base is compressing the outside of the baskets contents. More so than the innards, there is more back pressure from the sides than anywhere else.
Bear in mind the whole point of tamping is to evenly compress the coffee grinds throughout the basket. Consequently obtaining an even extraction. The objective being water passing through ALL of the coffee at the same rate of speed. It is easy to see that a 58mm flat based tamper will not necessarily help achieve that particularly well.
The best thing to do is use a 57mm coffee tamper if a flat based model is required. Tapping the side of the portafilter so that any loose grinds on the outside are push inwards. Then lay the tamper on top of those and rotate or spin the tamper so creating a flat surface for the coffee to pass through.
Using the traditional dosing methods of 7 grams for a single and 14 grams for a double. A 58mm tamper may not go far enough down the basket to tamp at all!
So in conclusion the advice is this: If you mainly use a double basket go for the 58mm convex tamper, if you use doubles and singles and dose 7g of ground coffee in a single basket and 14g of ground coffee in a double basket go for the 57mm tamper.
If like us you now only use a triple basket again go for the 58mm convex.
Remember if you have a Spaziale, a San Marco, a domestic Pavoni or an early Iberital expression, you will have to buy a 53mm tamper as any bigger based ones will not fit.
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