How can 30 lbs be a universal tamper pressure?

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jmatt
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Postby jmatt » Nov 26, 2006, 5:18 pm

OK - I hear about 30 pounds of pressure when tamping. Some tampers even have a "click" or other pressure mechanism set for 30 pounds.

However, I did some math:

A 49mm tamper covers 2.92 square inches. 30 pounds of pressure equals 10.3 pounds per square inch.
A 53mm tamper covers 3.42 square inches. 30 pounds of pressure equals 8.8 pounds per square inch.
A 58mm tamper covers 4.10 square inches. 30 pounds of pressure equals 7.3 pounds per square inch.

Looked at another way, to get 8.8 pounds of pressure with a 58mm tamper requires 36 pounds of force.
To get only 7.3 pounds of pressure with a 53mm tamper requires only 25 pounds of force.

So what's the rule? 30 pounds with a 58mm tamper, but only 25 with a 53mm? 30 pounds with a 53mm, but 36 pounds with a 58mm?

Or is the pounds of pressure irrelevant (within reason) so long as the tamp is consistent, and pull time is adjusted with grind fineness?

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Martin
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Postby Martin » Nov 26, 2006, 7:57 pm

BACK TO TAMPING BASICS

No experienced baristas that I've observed have been casual about their tamping (as in, "Oh, whatever, sometimes I smack, sometimes lean, sometimes just level," etc.) Althought there's no single "best" tamping technique (or pressure), a "consistent" technique is worth pursuing. I found that a using a 30 lb clicker tamper was an easy and unobtrusive way to achieve a consistent pressure baseline.

Several months of using a clicker tamp helped establish a kind of muscle memory for that pressure. When I got the tamper, I'd already been pulling shots for 3 years and realized a big flaw with the bathroom-scale-on-the-kitchen-counter training method. Feedback from the scale is largely visual with the scale dial (in my experience) overriding the pressure "felt" in my hand and arm. Basically, I had been training myself to stop pressing when the dial got to 30. Duh! With that kind of logic, I could probably train my basset hound to tamp.

There's no problem in using the clicker tamper as you'd use any other tamper (either don't reach or override the "click," annd I'd recommend one for anyone who doesn't pull dozens of shots each day.

Martin

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another_jim
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Postby another_jim » Nov 26, 2006, 11:04 pm

30 lbs is the number Schomer came up with. Presumably it works better than 15 or 45 pounds in his cafes. Most Italians don't tamp at all, but merely level the puck. Then I've seen people prepare for the Mr Universe contest by tamping.

The expert consensus is that any tamp or none, consistently applied, works. The real trick is to distribute and level the grinds perfectly, paying special attention that there are no gaps around the edge.

jmatt
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Postby jmatt » Nov 27, 2006, 9:47 am

another_jim wrote:30 lbs is the number Schomer came up with.



I'm confused how either of the two responses addresses the question?

Did Schomer come up with 30 lbs using a 58mm tamper? Does this mean a 53mm tamper should only use 26 pounds?

My point is that saying "30 lbs" seems ridiculous. 30 pounds of pressure over a basket the size of a garbage lid would be tremendously less than 30 pounds of pressure on grounds poured into a straw. Obviously those two extremes illustrate the point while being ridiculously outside the real range. However, there is a surface area difference between 53 and 58mm. If "30 lbs" is the answer for 58mm, then why is not 26 lbs the answer for 53mm baskets?

Coffee grounds (and anything else in the univers) react to pounds per square inch. Not to "pounds."

I guess I'm just confused on the whole theory.

Richard
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Postby Richard » Nov 27, 2006, 10:01 am

jmatt wrote:I'm confused how either of the two responses addresses the question?



Both responses seemed to clearly and concisely suggest that the actual pressure is of little importance but that a high degree of consistency is essential. To express that in other words, you're obsessing about something that's irrelevant; strive instead for consistency in technique.
Richard J. Wyble

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bill
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Postby bill » Nov 27, 2006, 10:05 am

I think Jim did answer the question. 'Consistency' in the amount of force you tamp with is the key, not the actual number. 30 lb. is just an amount of force that most people can apply the same every time. You may be different; just tamp the same every time!
Bill
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DC
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Postby DC » Nov 27, 2006, 10:09 am

You are technically correct - 30lbs of pressure is meaningless because of course pressure is a function of force and area. For example an espresso machine that gave 130lbs of pressure would be pretty meaningless, it's 130psi(9 bar) that's important.

However in espresso making it is just a guideline, as in 'aim to tamp about 30lbs on your scales' so if you tamp on your scales and get around 30 you're in the ballpark and you try and keep that to be constant. Tamping can't be as accurate as altering grind, so you try to scientifically alter grind and keep the tamping constant. Hence, you can grind finer or grind coarser whilst maintaining your tamp to try and hit around 25-30 seconds for 2 ounces (following golden rule). With an arbitrary number to aim at (30), this is easier, so you're changing as few variables at a time as possible.

As the others have said, distribution is more important. Get the right grind with a consistent tamp (the psi is irrelevant, it could be a hard tamp it could be a light tamp but be consistent) and perfect distribution of coffee and you'll get the shot you're after.

Hope this helps

DC

jmatt
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Postby jmatt » Nov 27, 2006, 11:02 am

Tada!! Now I think I get it. I didn't mean to be dense.

I just read more about 30 lbs than I do about consistency. It sounds like one could use 20, 25, 30, 35, 40, or whatever, so long as they were consistent AND you could squeeze through your 2 ounces of water in 25-30 seconds.

I would think that in a commercial environment, all of the barista's would need to use about the same pressure, assuming they were all getting coffee ground from the same grinder. Otherwise, wouldn't one barista get a shorter or longer pull than another, even if they were individually consistent in their tamping?

Oh well - I'm just a home user, so I only need to adjust my grind to me.

Thanks for the insight, all.

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Worldman
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Postby Worldman » Nov 27, 2006, 12:40 pm

My...how we all try to take these little bits of wisdom, bits of advice, and make them the Commandment of God!
FWIIW, I never measured my tamp pressure until a few months ago (OK, maybe a year ago). I have been making home espresso for >20 years and, after reading all the posts about 30# pressure, was curious at what pressure I was tamping. It turns out that I was tamping at ~34# pretty consistently. I have recently made a conscious effort to tamp at higher pressure since I am now under-dispensing coffee into the PF...but this is the subject for another post.

Anyway, I think the 30# is a good starting point and while you are correct that 30# downward force onto the area of a 58mm PF will yield less psi than the same downward force onto the area of a 54mm PF (or any PF of different area than 54mm diameter), it is good to acquire consistent and repeatable practices. Once your practices are consistent, you can then try to modify them to observe the result and hone in on that which works.

Len

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cannonfodder
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Postby cannonfodder » Nov 27, 2006, 8:30 pm

another_jim wrote: Then I've seen people prepare for the Mr Universe contest by tamping.




You mean my table should not creak when I tamp? :lol:

I have always viewed the 30 pound tamp as a suggested starting point, not a rule. I have used a light, 800lb gorilla and no tamp. As long as you are consistent in what you do the actual amount is almost immaterial.
Dave Stephens

 
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