Hey guys,

I've been anticipating the arrival of a new tamper (which happens to be flat) so I've been practicing with my flat tamper rather than my convex.

For the life of me I can't get consistent shot results with the flat tamper. Some are pretty good, some okay and some not so good tasting. The best ones happen to look the best and the others show obvious extraction flaws.

I can use my convex and things straighten out and the shots are quite good and more importantly consistent.

I don't get whats going on here, can convex really be that much more forgiving or has the convex led me to develop sloppy habits that the flat is now showing me?

Anyone else see anything like this?

I do.
Pulling doubles I use convex, pulling singles I use flat, tried the opposite way and results were not so good with doubles and pretty bad with singles - always the puck was sticking out from the walls.
By the way, I made myself a singles-week recently and also tried the different light tamp techniques, only coming to (the same - I tried it also at the very beginning) conclusion that 10g and normal hard tamp works best - otherwise the shots are simply spoiled by light streams and taste pale and bitter.

Hi Tim. I agree, convex pistons tend to be more forgiving than flat pistons. I don't really understand why. It may be that a convex piston pushes grinds away from the center of the basket towards the outer rim, which helps to prevent donut extractions. But it's a subtle effect, and I also get good extractions using a flat piston.

I believe most of the motions used when tamping which actually affect shot quality have little to do with compacting the puck, and more with distributing the grinds and sealing the rim. It may be worthwhile looking at your ritual from this perspective, and seeing how the tamper change will affect it. For instance, I level (with grinds out of a doser, no warranty for doserless, clumpy grinds) by nutating the tamper (the wobble motion as a tossed coin settles). This works a lot better with a curved tamper than a flat one.

What's the thickness of the piston?

The piston with the better reference to the basket rim produces a better shot more easily.
That's my FlatConvexCombinedVariousDiameter HO.

I have found that nutating or polishing motion and the use of the convex tamper reduce the chance of creating suction that dislodges the puck from the sidewalls of the basket when removing the tamper and believe this is the primary reason that these these motions and device modifications are useful in the tamping protocol.
Adrian

My approach is I dose the basket and level. I then use the finger tip tripod method (finger tips on edge of piston and basket to feel the tamper compress). I'm sure the tamps are level, although I have a harder time getting a perfectly level tamp with the flat tamper . I've been doing WDT to help rule out distribution.

The tampers are both cheapos. The flat is a solid stainless tamper and the convex is the budget lava tamp (bought on clearance and frankly a very comfortable tamper).

The pistons don't appear to be much different in size (mind you I lack calipers). If anything though the convex feels as it may be slightly smaller, but again I lack any meaningful way to measure this.

While I've not done any scientific experimentation on this situation I have been as methodical with my technique as possible and still can't explain what I'm seeing.

I'll keep playing around with the tampers and see what happens. Thanks to you all for the feedback. I'm not overly worried about it, just its been a while since I've used the flat and I was surprised to see the things I was seeing.

In my coffee lab all the additional variables got eliminated on the very begining! My flat is Espro Flat and my convex is Espro Convex (but mind you it's not just ordinary convex)

Tomorrow will make 6 weeks straight without a bad pull. I use a bottomless PF and in that time I have seen two or maybe three micro-sprites that lasted only a very short time— usually less than one second. Not bragging, but just establishing that my preparation procedure works well for me. I am still using the flat, 58mm one-piece aluminum tamper I bought when I got Silvia 7 years 10½ months ago.

I believe that no one method or set of tools will work for everyone in every situation. For example, if your coffee tends to clump with the grinder you are using you will need to deal with the dose/distribution/tamp differently than if you have a grinder that is clump-free(er).

I am with Jim on this one, mostly. I think the biggest difference is in the distribution of the coffee in the basket. The convex tamper will mush the grounds down and out somewhat evening out the distribution. A flat tamper simply mashes everything in place. If your distribution is off, then the density of the puck will be off. Something that is evident with a bottomless portafilter. I do also believe that some machines will favor a particular tamp curve. When I had the tamper road show at my house I tried many different tampers. At the time I was using a two group Faema that was very unforgiving. I did happen across a tamper shape that seemed to magically make the machine behave better. The same grind/dose/distribution, the only difference was the brand and shape of the tamper. But I must also say that I have used machines that it did not make any difference on.

Personally, I tend to use a flat piston for a machine with a flat shower screen and a curved piston for a curved shower screen. That way I have an even headspace across the entire puck. A good tamp will not make up for a bad distribution, but a bad tamp will ruin a good distribution. Then there is the school of no tamp at all. You just have to try a couple and see what works best for you. The nice thing, once you own a tamper, you can just purchase a new base for it to try different styles.