Tamper bottoms: Flat or convex?

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Which is better? Tampers with flat or convex bottoms?

Convex / domed
No preference
Total votes: 206

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#1: Post by HB »

(Images courtesy of Home-Espresso.com)
Dan Kehn

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#2: Post by ThaRiddla »

I'm a flat kinda guy.

I haven't ventured too much into the world of espresso tampers, but I'm doing some testing on new and experimental tampers now, so I might be changing my mind.

Whatever produces the best results.

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#3: Post by richard_bone »

Even though I don't have one at home and have almost no experience using them, I can't believe that a flat tamper would be better than a slightly convex one.

My reasoning (and it may be flawed), is that you'd have less of a tendency to channel on the edge of the puck because it would be pushed a bit against the wall of the basket...

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#4: Post by malachi »

Honestly, with good technique I've seen no real difference (either observed with the naked portafilter or tasted in the cup).

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#5: Post by PheasantCreek »

A lot of the channeling on the side I have seen and discussed with patrons have come from the tap method of tamping. People tend to tap the side of the portafilter too hard and it shocks the puck from the sides of the portafilter. You can see the shock waves from hitting a half-filled water bottle.
Geoff Corey

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HB (original poster)
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#6: Post by HB (original poster) »

I guess that I'm a flip-flopper. My first quality tamper was a flat Reg Barber (tall). The next was a Reg Barber convex (short). Then an Espro (flat). And now Ken Nye's convex.

It may be hairspitting, it may be my imagination, but my preference leans towards convex because side-channeling does seem less common (note that Reg Barber and espressocraft's are very gently domed). To be fair, the sort of channeling I'm referring to would be visually undetectable without a naked portafilter, i.e., nothing like this disaster:


I'm inclined to attribute a little of this occasional weepness at the edges to distribution faults, since I've noticed it occurs in pretty much the same location -- directly above handle. When I turn the portafilter 90 degrees while dosing, the weepy location changes. I won't swear to it (yet), but the lightly domed tamper bottom seems to reduce the edge-weepiness.

By the way, being a flip-flopper can't be all bad. David Schomer switched sides from 1999 to 2004.
Dan Kehn

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#7: Post by shadowfax »

I'm thinking about getting a convex espressocraft tamper to replace my rosewood Al tamper that I need to give to my sister. Are they still not selling them, or do I need to email them to get one ordered?

I'm also a little lost on the sizes (heights). I guess I should go measure my current one...

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#8: Post by framey »

I've got 4 flat and one convex tamper so I guess that puts me in the flat favouring camp :)

When I asked one of the more respected coffee houses here in Australia (Campos) why they chose convex tampers I was told that your tamper shape should match your basket shape, which in their case (Linea) was slightly convex. I'm not sure I've ever seen a convex basket?
Do baskets change shape with use ie the constant pressure of commercial coffee making?

I'm sure there was a very long and scientifically proven point on CG or Alt.C that a convex tamper will inevitabley place a great deal more pressure in the center of coffee and less toward the edges therefore giving technically an uneven tamp. The convex tamper I have is the Lava Deluxe and it seems to be quite rounded ie strongly convex. Anecdotally I haven't noticed any really difference between the Lava convex and my other flat tampers.


Ken Nye
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#9: Post by Ken Nye »

I just received an e-mail from Dan regarding this thread....so here are my two cents.

Regarding the flat vs convex issue, I still do not feel that one is truly better than the other. My own personal preference is mild convex. After speaking with many pro-baristi I beleive that the majority prefer convex as well, especially in Europe. If I had to put a number to it, I would say approx. 70% convex/30% flat.

I definitely notice better results with convex when working with triple baskets. They are more prone to channeling at the perimeter than doubles, and I feel that the convex provides a bit of reinforcement in that area. I have experiment with various degrees of convex pistons and feel strongly that a very mild convex with a smooth radius is best. No high points, etc. Currently we offer both flat and mild convex pistons at EC, but if I were to offer only one it would be mild convex.

There are many factors that play a bigger role in the tamping process than the shape of the piston. A level tamp, an even and full distribution of coffee in the filter basket, the distance between the puck and the group screen are all crucial to shot quality. Another often overlooked problem is the fit between tamper piston and filter basket. The majority of baskets that I have used, OEM or aftermarket, are slighty out of round and variances of as much as .5 mm (inside diameter) can be present. I generally like to see .5 - .7mm gap between piston and basket, depending on the amount of taper in the basket sidewall. Needless to say, if the fit is poor, the risk of channeling at the perimeter increases. This FB issue has become a pet peeve of mine, so much so that I have designed my own line of filter baskets with very specific tolerances (they will be out this summer).

I am unaware of any FBs that have a convex bottom when new. In a commercial environment baskets tend to stretch, and may appear convex. When our baskets stretch we replace them. Distortion in the bottom of the FB can cause irregularities in the filter holes which leads to uneven extractions.

Last but not least is handle length, shape, weight and balance. This mostly depends on hand size and tamping technique. We offer four "stock" lengths of handle, all evenly balanced and weighted. The shape that we choose took us over a year to design. Our goal was to design a line of tampers that could accommodate as many hand sizes and accepted tamping techniques as possible...not an easy task. Generally speaking, I find that tampers between 3.25"-3.50" in length suit the majority of people. We keep two sizes on the counter at our espresso bar and this seems to keep all of the baristi happy. It is also nice to go back and forth between sizes, this helps us practice different techniques and avoid too much repetition.

Hope this helps....
Feel free to post or e-mail with questions or input.

Ken Nye
Espressocraft, Inc.
Ninth Street Espresso

Abe Carmeli
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#10: Post by Abe Carmeli »

I have not fully tested it but I tend to think that if you use Staub, a flat tamper may be preferable. A convex in such case may produce an uneven "crater" in the middle of the puck
Abe Carmeli