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Permalink Reply by Brady on December 6, 2009 at 4:54pm

Eric said:

Kevin Ayers said:

On your polished tamps, are you putting downward pressure on the puck while you polish it? The polish I was taught, is too let go of all pressure then spin the tamp freely. Also, a 5.4 gram difference in the puck weight is huge, how many times did that happen? Have you tested your dosing weights by popping baskets out after you tamp them, and then weighing them, just to make sure you're being consistent with your pre-extracted weight?

I think I worded this funny, we weighed the actual espresso shot and the unpolished shot was 5.4grams heavier... So as a response Brady, I dont think that your question"Did they both gain the same amount of water weight but the polished puck had a larger amount of solids extracted, thus resulting in a lighter spent puck?" would be right since we are finding that a larger volume/weight in the unpolished shot...

Wait... so you aren't talking about a greater shot density, there's more volume in the shot? Maybe we shouldn't be surprised that the shot is heavier then... Perhaps you should try cutting the shot off at the same volume and making your comparison that way? Just a thought.

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Permalink Reply by Eric on December 6, 2009 at 6:03pm

Brady said:

Wait... so you aren't talking about a greater shot density, there's more volume in the shot? Maybe we shouldn't be surprised that the shot is heavier then... Perhaps you should try cutting the shot off at the same volume and making your comparison that way? Just a thought.

I think if I can get my or someone else's hands onto a TDS meter and measure the shots to see we can tell if it just more water weight or density, then I can only assume it could be a bit of both. I also am thinking that with Josh's tests on the GB5 which has a type of pre-infusion, that the consistent heavier weight of the unpolished pucks that it kind of indicates that pre-infusion might not have much of an effect on the end shot weight for each. But, on the Linea we were working with here in MKE I thought our shots tasted better when un-polished. I am wondering if the pre-infusion on an unpolished puck lent to the over-extraction Josh was talking about? We never really noticed any over-extraction in our shots and never had the pre-infusion... and I must be clear that I am not set in liking one way over the other. As far as cutting off the shots at the same volume, what do you think this would be an indicator of? Would it help more doing this specifically if we had a TDS meter so we could measure the solids at the same volume to see if there is a difference? or do you think that timing the shots the same is not an accurate way of keeping the tests scientific?

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Permalink Reply by Brady on December 6, 2009 at 6:30pm

Eric said:

Brady said:

Wait... so you aren't talking about a greater shot density, there's more volume in the shot? Maybe we shouldn't be surprised that the shot is heavier then... Perhaps you should try cutting the shot off at the same volume and making your comparison that way? Just a thought.

I think if I can get my or someone else's hands onto a TDS meter and measure the shots to see we can tell if it just more water weight or density, then I can only assume it could be a bit of both. I also am thinking that with Josh's tests on the GB5 which has a type of pre-infusion, that the consistent heavier weight of the unpolished pucks that it kind of indicates that pre-infusion might not have much of an effect on the end shot weight for each. But, on the Linea we were working with here in MKE I thought our shots tasted better when un-polished. I am wondering if the pre-infusion on an unpolished puck lent to the over-extraction Josh was talking about? We never really noticed any over-extraction in our shots and never had the pre-infusion... and I must be clear that I am not set in liking one way over the other. As far as cutting off the shots at the same volume, what do you think this would be an indicator of? Would it help more doing this specifically if we had a TDS meter so we could measure the solids at the same volume to see if there is a difference? or do you think that timing the shots the same is not an accurate way of keeping the tests scientific?

Just making sure that you extract the shots for the same amount of time is not giving you an apples-to-apples comparison. If that was the method you used to determine when to cut the shot off then all the higher weight indicates is that one pulled faster.

To me, the way to do the comparison is to dial both shots in and then compare them. If you have any other variation, your differences may well be due to some other factor (like shot volume).

What your work to this point has demonstrated is that an unpolished puck extracts faster. An interesting observation, but I think we can find out more stuff if we keep at it.

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Permalink Reply by Eric on December 6, 2009 at 10:53pm

Brady said:

What your work to this point has demonstrated is that an unpolished puck extracts faster. An interesting observation, but I think we can find out more stuff if we keep at it.

I was reading Scott Rao's "The Professional Barista's Handbook" tonight and was intrigued by just a few things that may seem to counter the logic that all that is happening is the espresso extracting faster. In the book Scott talks about fines migration in the puck over the extraction time and how pre-infusion limits the fines migration by saturating the coffee and such. I think what we may be potentially experiencing here in Milwaukee on the Linea, which does not have pre-infusion, is more of the fines migrating into the actual espresso shot and contributing to what we are sensing as a fuller shot. Where as on a pre-infusion machine like the GB5, the unpolished shot is coming off more bitter and over-extracted because the fines are possibly being limited and therefor over-extracted. And another idea that I had previously touched on about the top of the puck extracting more was discussed in the book too. What I am thinking now about the unpolished puck and how with the surface being more porous and susceptible to saturation that it is increasing the flow and the start time of the actual extraction of the whole puck unlike the polished puck where the polish creates resistance and increased extraction on the top of the puck. After all, in the book Scott says nothing about polishing the puck, almost indicating that he himself does not polish... and I am just paraphrasing the book when it said roughly that the tamp itself polishes the puck for extraction. The final thing I took from the book is that during a normal extraction, the water saturates the coffee and exchanges more fines with the larger particles in the puck. Basically saying that in a pre-infused puck that these fines would be more restricted, and on a polished puck the over all saturation and exchange would occur later in the extraction because of the relative resistance from the polish. This could also be why on the pre-infusion with the tests on the GB5 that the polished shots came out better. I am still very interested to see and test my hypothesis on a TDS meter and see the results. Let me know what you all think.

And as a note the 5.4 grams of weight difference between the polished and unpolished pucks roughly translates to .19oz difference for the double shot. Something to think on...

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Permalink Reply by Eric on December 7, 2009 at 5:40pm

My conclusion on whether or not to polish after a tamp...

For the past few days, I would not say that I have been obsessing over whether or not polish an espresso puck after tamping, but I would say that it has not been far from my mind. I have very realistically been looking at so many aspects to this situation that it may have inhibited my view to see the what the physics of the situation dictate. I am not going to pretend that I didnt find any of our results fascinating in my previous blog post, but I will say that maybe and just maybe what was really happening, is that our tests were not accurate enough to specifically address the question at hand. What I mean is this, keeping all aspects(variables) the same in the situation to be scientific with respect to all sorts of weight tests and differences, as well as time and espressos visual cues we as much as we could have like to can not scientifically enough extract(pun intended) the necessary information to indicate one way or another if indeed polishing does or does not affect shot extraction. (I am sorry if that sentence was insanely incorrectly worded and not properly grammer-ized.) I had the pleasure of talking to Scott Rao tonight on the phone for a few minutes, and after listening and conversing, it came to my attention that whether or not a puck is polished, whether or not you tamp light or hard the major big guy in the situation is how much pressure is coming down onto the puck. Scott said the words "540 pounds" and "pancake" and I got hungry. No, I'm just kidding, but seriously, what he was saying made perfect sense in that even if you were to absolutely scientifically test this and made sure all the variables would not change that without a doubt the results could be that one was somehow different, but overall negligible. The focus should instead be primarily on those variables that do account for some huge changes(ie a tamp level, grind particle size being dialed in correctly and most importantly being in the golden taste zone of what is good. This has although not stopped my curiosity with the subject espresso... the questions and tests must go on!!!!!!

So my personal conclusion... Tamp once, do not bump, do not polish, just do it right the first time...

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