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Permalink Reply by Fraser Jamieson on February 1, 2010 at 12:33pm

The short answer is: I don't know.

However, I changed to a Reg Barber C-Ripple a few months ago, from a Reg Barber C-Flat, and without me saying anything to anyone, customers began telling me that the espresso was better than ever.

OK, so maybe I had started paying more attention; maybe other factors came into play. Whatever. All I know is that my the two tampers look identical when sitting on the machine so the only person who know about it was me.

I'm guessing that the ripple idea actually works.

The machine I'm using does pre-infusion on the single settings but not on the doubles. For lattes, I tend to use the semi-auto keys because I can't see into the large cups we use; for espressos, though, I dose manually and will typically start and stop the water quickly, then restart and run to the length the customer enjoys.

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Permalink Reply by scott@herkimercoffee.com on February 1, 2010 at 3:50pm

Since you've asked, this is something we've spend a ton of time on...

I've been looking for the perfect tamper for quite some time as I don't have a C and C machine to make my own. Basically I want the tamper to match the shape of the diffusion screen as closely as possible. The reason for this is simple: to allow even expansion at the initiation of flow. This means that if all things are operating properly (the screen is clean and in good shape-not dented or flattened from use) the water column will contact the entire surface of the coffee all at one time. This allows the coffee to expand as a whole unit and rise to meet the screen uniformly. A small amount of room for expansion allows the surface area (grind) to do the work of providing resistance against flow. 1 to 1.5mm is all that is necessary. More than that -(2mm or greater)- allows too much rise resulting in a large quantity of particle migration (fines dropping to the bottom) causing overextraction and interupted flow. No room for expansion (an overpacked basket) requires a coarser grind to allow any flow to occur resulting in either an underextracted shot or any overly long flow duration (to balance sugar and colloids with acid) which causes the sugars to fall apart making the texture and aftertaste suffer.

Different infusion methods will yield slightly different results. Full pressure infusion (8.5 to 9 bar) from beginning to end requires a perfectly level tamped surface that matches the shape of the screen to avoid channeling. Low pressure initial infusion (4 bar) followed by full pressure is more forgiving on tamping variations by allowing the coffee to expand slower but still will show directional flow if the surface was angled. Low pressure followed by ramped or staged pressure is a small amount better in the forgiving department as the expansion progresses as the pressure builds. Even though pressure variation helps minimize the detriments of poor tamping it does not eliminate them. This means using a tamper that does not match your screen will allow for a path of lesser resistance for the water to flow toward before allowing infusion causing an uneven expansion. Flat screen with a round tamper equals an uneven rise in the center of the coffee whereas a flat tamper on a rounded screen equals an uneven rise on the outer edges of the basket.

Long story short, disparate screen and tamper shapes cause expansion problems and channelling which make the coffee suffer. Any path of lesser resisitance equals underextraction through that path or channel. Underextraction means acid out of balance even in small amount caused by a slight discrepancy. To eliminate that possibility your variables have to match. Flat tamper with a flat screen. Round tamper with convex screen. If the curves don't match you will create problems so take care in matching the radius of the screen to the tamper head.

We found the Caffelat 58mm Curved Tamper to be the closest match to the screens we are using on our Synesso machines. This is the same screen used on alot of machines including La Marzocco. Take your screen with you when checking out tampers and you should be able to find one that matches.

Hope that helps,
Scott

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Permalink Reply by Brady on February 1, 2010 at 6:05pm

scott@herkimercoffee.com said:

Since you've asked, this is something we've spend a ton of time on...

I've been looking for the perfect tamper for quite some time as I don't have a C and C machine to make my own. Basically I want the tamper to match the shape of the diffusion screen as closely as possible. The reason for this is simple: to allow even expansion at the initiation of flow. This means that if all things are operating properly (the screen is clean and in good shape-not dented or flattened from use) the water column will contact the entire surface of the coffee all at one time. This allows the coffee to expand as a whole unit and rise to meet the screen uniformly. A small amount of room for expansion allows the surface area (grind) to do the work of providing resistance against flow. 1 to 1.5mm is all that is necessary. More than that -(2mm or greater)- allows too much rise resulting in a large quantity of particle migration (fines dropping to the bottom) causing overextraction and interupted flow. No room for expansion (an overpacked basket) requires a coarser grind to allow any flow to occur resulting in either an underextracted shot or any overly long flow duration (to balance sugar and colloids with acid) which causes the sugars to fall apart making the texture and aftertaste suffer.

Different infusion methods will yield slightly different results. Full pressure infusion (8.5 to 9 bar) from beginning to end requires a perfectly level tamped surface that matches the shape of the screen to avoid channeling. Low pressure initial infusion (4 bar) followed by full pressure is more forgiving on tamping variations by allowing the coffee to expand slower but still will show directional flow if the surface was angled. Low pressure followed by ramped or staged pressure is a small amount better in the forgiving department as the expansion progresses as the pressure builds. Even though pressure variation helps minimize the detriments of poor tamping it does not eliminate them. This means using a tamper that does not match your screen will allow for a path of lesser resistance for the water to flow toward before allowing infusion causing an uneven expansion. Flat screen with a round tamper equals an uneven rise in the center of the coffee whereas a flat tamper on a rounded screen equals an uneven rise on the outer edges of the basket.

Long story short, disparate screen and tamper shapes cause expansion problems and channelling which make the coffee suffer. Any path of lesser resisitance equals underextraction through that path or channel. Underextraction means acid out of balance even in small amount caused by a slight discrepancy. To eliminate that possibility your variables have to match. Flat tamper with a flat screen. Round tamper with convex screen. If the curves don't match you will create problems so take care in matching the radius of the screen to the tamper head.

We found the Caffelat 58mm Curved Tamper to be the closest match to the screens we are using on our Synesso machines. This is the same screen used on alot of machines including La Marzocco. Take your screen with you when checking out tampers and you should be able to find one that matches.

Hope that helps,
Scott

Wow. Thanks for sharing this.

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Permalink Reply by Aaron Duckworth on February 1, 2010 at 9:02pm

Hey Scott! Thanks for the awesome reply! Being in Kansas City, the coffee showrooms are few and far between and it gets expensive ordering everything in to play with. But, I have a paddle group Marzocco FB80 headed to KC right around the start of May so I'll get to do my own experiments soon enough. The tamper base I was eyeballing was Reg Barber's S/S - US curve and I'd be interested to see it side by side the Cafelat

I'll have to stop in to Herkimer next time I'm in town. I used to live between Greek Row and the U-Village and I know right where you're at. I may be coming out in a couple of months so it might be sooner than later. Thanks again for taking the time to write all that out, you confirmed some of my own suspicions (needing to make the puck shape match the screen shape) and raised points I had not considered like the varying infusion methods. I'm way excited to try it all out and will definitely get my hands on a Cafelat tamper. Later.

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Permalink Reply by Jason Haeger on February 2, 2010 at 6:48am

I don't buy the logic of matching shape with dispersion screen.

It always made more sense to me to match it with the filter basket. Personally, I'm not a very big fan of the LM baskets, unless up-dosing is the norm. (which for me, it isn't)

On average, I'm with you, Duck. I like the US curve. I get the most even beading across multiple machines and baskets from a US curve.

Just my $.02.

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Permalink Reply by Bryan Wray on February 2, 2010 at 7:04am

Haven't played with a C-Ripple yet (need to) but I can tell you that I most certainly prefer a US Curve (aka- slight curve) to anything else, for the same reason that Jason mentioned.

I guess my thing with the matching of the piston shape to the screen is... who's to say the water flows from the screen in the same shape as the screen? Pretty sure it doesn't. Also, I get no channeling (like ever) from my US curve against LM's flat screen. I just don't think the puck expands as much as people think. They see the impression of the screen on the puck and don't assume that perhaps its from the giant, sucking, 3-way pulling the top layer against the screen. Am I wrong about this? I truly don't know.

Sorry to derail this thread...

-bry

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Permalink Reply by Jason Haeger on February 2, 2010 at 7:25am

I don't think you're wrong about it. I was going to talk about it, but decided not to to avoid being read the wrong way.

I've talked about this a lot over the last few years, and I'm definitely not the first, and not the only one.

It doesn't take much experimentation to see what happens at initial contact. It also doesn't take much to imagine what happens once pressure is reached. The expansion happens when the valve opens, and all of that pressurized water in the puck is forced through the path of least resistance: upwards.

But that's off topic.

I'm not fond of the c-flat. I'd prefer either a straight flat or convex. I get more donut-beading from flat tampers than from us curve. I get more center-beading from the full convex than the us curve.

I figure the goal is even extraction. Visually, I get a more even extraction from the US curve. I've had some very tasty shots from miserable looking pours, but the tastiness is analogous to a melange, except it's about different extraction rates instead of different roast levels.

Everyone should serve what they like, but consistency is just as important as quality. And here I've gone off on yet another tangent.

Bryan Wray said:

Haven't played with a C-Ripple yet (need to) but I can tell you that I most certainly prefer a US Curve (aka- slight curve) to anything else, for the same reason that Jason mentioned.

I guess my thing with the matching of the piston shape to the screen is... who's to say the water flows from the screen in the same shape as the screen? Pretty sure it doesn't. Also, I get no channeling (like ever) from my US curve against LM's flat screen. I just don't think the puck expands as much as people think. They see the impression of the screen on the puck and don't assume that perhaps its from the giant, sucking, 3-way pulling the top layer against the screen. Am I wrong about this? I truly don't know.

Sorry to derail this thread...

-bry

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Permalink Reply by Bryan Wray on February 2, 2010 at 7:34am

Aaron, to get back to your original question a little more...

I think the same principals that apply with full pressure machines would apply to pre-infused machines, just more forgiving on all fronts. Then again, the small area of uncertainty is probably exactly why you are asking this question isn't it... :0)

-bry

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Permalink Reply by Brady on February 2, 2010 at 11:53am

Bryan Wray said:

...
Sorry to derail this thread...

-bry

This could be an interesting discussion of its own. I started an offshoot along those lines here:
http://www.baristaexchange.com/forum/topics/inside-the-crucible-wha...
So, let's continue to discuss that over there, and this over here.

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Permalink Reply by Fraser Jamieson on February 3, 2010 at 12:24pm

I've tried all of the different designs from Reg Barber, except for the flat ripple; that one I haven't. I've also used undersized flat tampers and changed my technique accordingly. My semi-educated guess is that success has a great deal to do with the actual tamping style employed. The logic behind using the US curve makes a great deal of sense to me...but I've personally had better pulls with the C-Flat/C-Ripple.

Basically, I do a 2 Kg tamp/ knock off stray grounds/ 14 Kg. tamp/ then turn the portafilter a third of a turn while under pressure. I'm getting good flavous and my pucks fall out when I turn my portafilter upside down.

The reason they do that, I'm pretty sure, is that they are sucked up against the shower screen when the three way valve dumps the pressure.

Again, back to the pre. or non-preinfusion question: each machine is pretty much it's own species of animal. I'm not so sure that there can be a straight answer.

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