Sorry to drag up an old post (I've been away from these forums for a long time) but seeing as I started it it should be okay :P
This post has done exactly what I intended it to do, for everyone to go back and think about their dosing and tamping techniques.
I'm not saying tamping has NO effect on the rate or quality of extraction, what I am saying is that if you compress the grounds enough to remove voids in the coffee bed, tamping any harder will produce a negligible result in net extraction times (assuming you're aiming for a set EBF, TDS and extraction yield). It's quite obvious that no tamping will produce a gusher. Think it's really important to aim for a consistent tamp and dose and then you're able to work with just grind as a variable for tweaking flavour.
Announcement
Collapse
No announcement yet.
Why tamping doesnt matter as much as you think
Collapse
X
-
Ok, my 2c.
Firstly, I think it's worth keeping in mind that scientific theory of any sort (in this case fluid dynamics/physics) is intended to explain what we observe. If there is a discrepancy between the science and the observation, it is the science which is flawed, not the observation.
I have scales which measure to 0.1gm, and have a convex scraper with which I shape and level the ground coffee in the basket. My coffee machine has PID controlled temperature. I mention this because my dose between two shots (with the same coffee of course) is consistent, my distribution of ground coffee is consistent, and my extraction temperature is consistent. When I pull a shot, the only significant variable is, in fact, tamping pressure. If I pull a shot with a very light tamp, vs. one with a very firm tamp, there is a significant and noticeable difference in the dwell time, extraction rate and flavour of the finished shot which can only be attributed to a variation in the tamping pressure. In this sense I would say that tamping pressure does matter, as it directly and noticeably alters the outcome (my doppio). I will add that I have learnt to err on the slightly lighter side with tamping pressure, as I found a very firm tamp (20kg or more) results in an increased tendency for channelling around the edges of the puck (I use a VST basket, which I think is more prone to edge channelling than most others), to the extend that I can get a slower extraction rate at low-mid tamping pressure than if I squash the beejesus out of the puck. As someone mentioned earlier, I think the ideal pressure is just before the point at which the puck will no longer compress further. Obviously everyone's idea of a significant difference in coffee output is subjective, but given this site is called coffee snobs (not coffee hubbards) I have to say that in my opinion tamping pressure is a significant variable factor (along with a number of others) in producing a decent coffee shot.
- Flag
Leave a comment:
-
While I would never argue with the science behind your claim - as my mama used to say never argue a point you know nothing about - I will share my real world experience. My first machine was a cheap Sunbeam $120 machine and a Breville (equally cheap) grinder, from Big W. When I switched to a non-pressurized basket (first upgrade of many) I could never produce any creme worth a damn - actually my coffee was worse. So I switched to fresh coffee purchased online instead of supermarket. Still little improvment. So I got a heavy steel tamp that was an exact fit for my new basket and still had issue slowing the extraction rate down because I couldnt grind fine enough. Seeing I couldnt grind finer my only option was to exert more pressure on the tamp, and when I say more pressure - I mean A LOT more pressure. This, combined with overdosing, actually produced some pretty decent shots and slowed down the extraction to the required time.Originally posted by EspressoSchool View PostThe magical 15 kg of "force/pressure" has often been used as a benchmark for tamping in industry. It gives baristas a baseline to work from – 15 kg of downward "force" is merely a trade off between the compactness of the bed of coffee and preventing RSI (repetitive strain injury) for baristas tamping hundreds of group handles a day. As long as you are consistent, it does not matter how hard you tamp.
The reasoning is this: tamping harder or softer will have negligible impact on an extraction flow rate once the coffee bed has been tamped with sufficient pressure to remove any air pockets between coffee grinds. 9 bar of extraction pressure is 16 times greater* than the pressure of a 15 kg tamp. Tamping pressure is immediately alleviated during the period when the dry coffee is wetted and once the extraction is in full swing will always be much less than pump pressure.
So when someone says tamp harder to slow down an extraction, I call bs!* :
Discuss, debate, theorise..... 8-)
Fast foward to present and with my current setup of a La Pav Pro and Jolly Grinder, Tamping is very low down on my list of concerns. With the basket size I have actually gone back to the original plastic tamp from the Sunbeam which happens to be an absolute perfect fit for the 49mm La Pav. So my completely non-scientific, seat of my pants, will-do-it-till-I-find-something-better, opinion is that when you have full control of all the variables then tamp is not important. The only caveat I place on this is that your basket and tamp must be a snug perfect fit.
- Flag
Leave a comment:
-
If only it were that simple, this wouldn't be an issue worth discussing. You point out in step three that all other variable must be kept the same - this is not easy and I think you'll find there's a fair bit of variability. So you really need another important step. Do (say) five shots at each pressure and look at the variations between and with each pressure.Originally posted by Vinitasse View PostTo test the scientific principle all you need to do is to test the two extremes and this will allow you to form a hypothesis. One... don't tamp at all and run your usual shot through the very loose grounds and I can assure that you will have a very sinkable gusher. Two... tamp the bejezus out of your next shot and you will probably choke the machine because your OPV prevents your machine from putting out enough pressure to squeeze the water through the very compacted grounds. Three... keeping every other variable the same, vary the tamping pressure and watch your shot clock. Lower pressure tamps will yield faster shots and firmer tamps will drag things out. Therefore, one can readily conclude that the duration of the shot can be GREATLY influenced by the tamping pressure of the grounds in the portafilter. Shot duration has a great effect on extraction density, temperature and overall quality so I would have to say that tamping DOES MATTER a great deal.
People who have done this sort of experiment report that there IS a significant difference between no tamp and a light tamp, but that the difference between a light tamp and a firm tamp is minor (see for example Illy et al., 2005, pg 278). Does "minor" mean insignificant? An even more difficult question to answer I reckon.
- Flag
Leave a comment:
-
Interesting read, funny how we get stuck on the finer points and theories.
My view is, the man who started this threas, David, competes at an international level as a barista and I believe he is studying engineering if not finished already. He would have made more coffee than 90% of the coffee snobs members put together. So when he suggests something I tend to give it credit.
Tamp pressure would effect per infusion if you do it, if not, find something that suits you and is repeatable and keep doing it. If you want to change something, change one thing at a time to test.
Remember to enjoy it and not get bogged down in theories
- Flag
Leave a comment:
-
To test the scientific principle all you need to do is to test the two extremes and this will allow you to form a hypothesis. One... don't tamp at all and run your usual shot through the very loose grounds and I can assure that you will have a very sinkable gusher. Two... tamp the bejezus out of your next shot and you will probably choke the machine because your OPV prevents your machine from putting out enough pressure to squeeze the water through the very compacted grounds. Three... keeping every other variable the same, vary the tamping pressure and watch your shot clock. Lower pressure tamps will yield faster shots and firmer tamps will drag things out. Therefore, one can readily conclude that the duration of the shot can be GREATLY influenced by the tamping pressure of the grounds in the portafilter. Shot duration has a great effect on extraction density, temperature and overall quality so I would have to say that tamping DOES MATTER a great deal.Originally posted by Cadan View PostSo I believe tamp pressure can have some effect.
- Flag
Leave a comment:
-
Yes I agree with BOSW about the tamp pressure effecting the delay in the start of the shot
I have had shots start a bit tight so next pour I have tamped with a bit less pressure without changing the grind or dose and had a more even start to the pour
So I believe tamp pressure can have some effect.
- Flag
Leave a comment:
-
From what I can work out using my machine, baskets and modest knowledge, tamp pressure (within a reasonable range) has a greater impact on the delay than it does on the overall extraction. Thus, if I find that it is taking 10 seconds for the first drop of coffee to emerge, but that the rest of the extraction looks normal....I ease up on the pressure. I'm sure there are 6 different ways to arrive at the same result though.
- Flag
Leave a comment:
-
Interesting comment! And I think you are right! will need to taste and see
- Flag
Leave a comment:
-
I guess you mean giving the puck a level surface ?...Originally posted by shawty View Post+1
....as well as the tamper compacting the puck evenly to start with.
compacting evenly is debatable due to the base profile of the basket ( especially singles), and how level the surface of the untamped grounds is .
IE.. if a shaped "barister guide" is used.
Generally speaking, using a flat faced tamper, the outside of the puck will be "compacted" more (denser) than the center .
- Flag
Leave a comment:
-
+1Originally posted by saoye View Post
To me I agree to some extent but the function of the tamper nowadays for me is to indicate correct dose level as well as reduce the mess I make in the tamping process. I know a correct dose by the tamp level as well as the pressure on the tamp. I grind so that when I press down on the tamper there is certain feel on the tamp because you can underdose and lightly tamp to get to a certain level and overdose and gorrilla tamp and still get to the same level...it's consistancy so grind and tamp to a pressure to know what's in your basket.
I agree totally with this as well as the tamper compacting the puck evenly to start with.
- Flag
Leave a comment:
-
But you keep your Reg BarberOriginally posted by JamesM View Postdunno about tamping pressure, but polishing, and precision fit tampers, are BS.

To me I agree to some extent but the function of the tamper nowadays for me is to indicate correct dose level as well as reduce the mess I make in the tamping process. I know a correct dose by the tamp level as well as the pressure on the tamp. I grind so that when I press down on the tamper there is certain feel on the tamp because you can underdose and lightly tamp to get to a certain level and overdose and gorrilla tamp and still get to the same level...it's consistancy so grind and tamp to a pressure to know what's in your basket. I do weigh the beans on a scale but the scale is to the nearest gm so that could be up to 4 extra beans in the grinder. doesn't sound like much but it could mean an underdose or an overdose. I compensate by (don't do this at home
) 3/4 locking if overdose or full lock to max if underdosed. The reason for the locking position is again to allow for correct expansion of the puck. It's dangerous to partially lock your pf to compensate for an overdose as you may risk a rocketing pf into your beautiful cup. Do so at your own risk. Or better yet, don't do it, and instead redose correctly.
Now regarding a precise fit or not, again to me it's about the level of the tamp to indicate correct dose...if I have a stack of untamped ground all around the basket, I've not really tamped to tell me that I've got the right amount of grind in the basket.
HOWEVER, if you use other indicators to get the right dose other than the tamper then there is no argument, just use the plastic tamper on your commercial grinder or even use the plastic tamper that came with the machine you bought.
I like to polish to get rid of that annoying static ground that might stick to the bottom of my tamper. It does nothing and yes it might aggitate the puck if you're rough...but meh...as everybody against fussy tamping says, the swell of the puck and pressure will sort that out anyway.
- Flag
Leave a comment:
-
dunno about tamping pressure, but polishing, and precision fit tampers, are BS.
- Flag
Leave a comment:
-
I don't know the mathematics behind it but I find that tamping pressure does affect the taste of my coffee. I tend to get thin underextracted gushers whenever I try to reduce the tamp pressure (under 15kg pressure) even though the coffee in the portafilter seem to be compacted with even distribution.
- Flag
Leave a comment:
-
I think you are getting closer John Smith, but perhaps not quite there. It isn't that the pressure expands the puck, it's the water absorbing into the pores within the coffee (I'm not talking about the void space between the grinds here, but actual pores in the coffee).
Grind size will affect the rate at which this occurs, as a finer grind = greater surface area = faster absorption. I wouldn't speculate as to whether this specifically is an issue for quality or not.
Considering the factors of dose, grind, and tamp together, something has just dawned on me. Perhaps the interrelation between the three factors is more important than any of them in isolation . Thinking out loud:
There seem to be "rules of thumb" for puck compression (relative to the top of the basket), tamp pressure, and dose. Ignoring the dogma, we can probably arrive at those same requirements working backwards.
- To get an even extraction (or best attempt at one), we probably want an essentially fixed bed (i.e. minimal movement of coffee).
- To achieve a fixed bed the expanded puck should contact the shower screen with enough force that the grounds don't move when the water passes through them.
- Tamping allows "overfilling" of the basket, so that there is enough coffee in it to fill the whole volume once wet and expanded. If the same amount of wetted coffee would normally take up more volume than is available under the shower screen, then the puck will compress against it.
- An additional factor is that to achieve a good extraction (i.e. all the stuff you want, but little of the stuff you dont), you need a slow enough flow to allow extraction of the coffee oils, but not so slow that the tannins have time to extract.
- Working to a constant tamped depth effectively fixes one of the variables (pre-expanded volume), which aids consistency. Since the volume is fixed, there is a narrow range of grind size, dose and tamp combinations which will give result in the having the right mass in the basket to give a fixed bed post expansion.
So perhaps the purpose of the tamp is simply to fit sufficient mass of coffee into the basket to allow a fixed bed "post expansion".
- Grind too coarse, under-dose and undertamp, and for the same post-tamp puck there won't be enough coffee to create a fixed bed.
- Grind too fine, or overdose and overtamp and for the same post-tamp puck height, there is too much coffee in the basket and the flow will be too slow.
This suggests to me that overtamping and undertamping are problematic only because if you are working to a fixed tamp depth, they mask the real problem (under/over dosing and/or grinds being too big/small). It also suggests that undertamping is more problematic because it will not result in a packed bed post extration, wheras overtamping is less of a problem provided you don't overdose (as the result will just be a reduced tamped volume).
Thus the relationship between grind size, tamp pressure and puck height (with a few simplifing assumptions, ignoring a couple of factors
).
Of course, this is just a thought experiment, and I am certainly not an expert.Last edited by MrJack; 8 August 2012, 12:59 AM.
- Flag
Leave a comment:

Leave a comment: