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Dose consistency of weighing coffee in basket versus portafilter+basket

Postby erics on Mon Feb 20, 2012 11:15 pm

HB wrote:I used to remove the portafilter retainer clip so I could drop in the basket after weighing as advocated in Digital espresso or a way to consistency. But I've switched to weighing the whole portafilter and knocking out the puck/wiping the basket clean... My change in routine was simply to streamline my morning workflow.

Just to inject some common(?) sense - although that common sense could be out of place. Let's just say that:

a. An empty portafilter (no basket, no spring) weighs 500 grams.
b. A typical doubles basket weighs 28 grams.
c. A typical espresso dose is 15 grams.

How reasonable is it to ask a scale to differentiate between 528 grams and 543 grams OR 28 grams and 43 grams? How consistent is it and does this consistency, or lack thereof, matter to the end user?

Regardless of the source, baskets are very inexpensive relative to the cost of the machine.


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Postby mitch236 on Tue Feb 21, 2012 9:02 am

erics wrote:Just to inject some common(?) sense - although that common sense could be out of place. Let's just say that:

a. An empty portafilter (no basket, no spring) weighs 500 grams.
b. A typical doubles basket weighs 28 grams.
c. A typical espresso dose is 15 grams.

How reasonable is it to ask a scale to differentiate between 528 grams and 543 grams OR 28 grams and 43 grams? How consistent is it and does this consistency, or lack thereof, matter to the end user?

Regardless of the source, baskets are very inexpensive relative to the cost of the machine.


This is exactly what I found. My measurements were too inconsistent with a scale that had a range high enough to measure the pf with basket (1000gm). Once I switched to a small digital scale with a 100gm range, my consistency went way up.

I took the clip out and now put the scale on the grinder fork and that holds my basket. All very easy and neat.
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Postby spiffdude on Tue Feb 21, 2012 9:22 pm

I would assume that a 1000g scale advertising a 0.1g precision can actually get close to that. Otherwise it's just blatant false advertising and that never happens on ebay :wink:

I guess that a 100g scale advertising a 0.1g precision is maybe more accurate, but are we talking about a 0.1g difference here? I usually don't bother with 0.1-0.2 grams differences anyway... Much too busy banging my portafilter with clipped in basket on the knockbox.
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Postby HB on Tue Feb 21, 2012 11:34 pm

For what it's worth, I checked and found that the scale's precision was within ~0.2 grams but its accuracy suffered. That is, if I added a small fixed weight (say 18 grams) to the scale already occupied by a portafilter, the reading was the same each time within ~0.2 grams. But if I weighed the elements separately, the sum of the elements was not the same as the parts weighed all at once by a much wider margin.

So the scale is highly precise under these circumstances, but not highly accurate:

Image
High precision, low accuracy

The lesson here is that if I want to report accurate doses to others, weighing the portafilter+basket+coffee on the scale together and subtracting the weight of the portafilter+basket is less accurate than weighing the basket+coffee and subtracting the weight of the basket.
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Postby cafeIKE on Wed Feb 22, 2012 12:44 am

mitch236 wrote:I took the clip out and now put the scale on the grinder fork and that holds my basket. All very easy and neat.

Bend the clip. Even a ridged basket is easy to insert

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Postby mitch236 on Wed Feb 22, 2012 7:44 am

cafeIKE wrote:Bend the clip. Even a ridged basket is easy to insert


Why? I don't see a downside to the way I'm doing it now.
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Postby Viernes on Wed Feb 22, 2012 11:12 am

mitch236 wrote:Why? I don't see a downside to the way I'm doing it now.



How do you knock out the puck without dropping the basket?
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Postby mitch236 on Wed Feb 22, 2012 11:25 am

Viernes wrote:How do you knock out the puck without dropping the basket?


Easy, I just put my thumb on the lip of the basket when I hit the bar. Works perfectly most of the time.
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Postby mitch236 on Wed Feb 22, 2012 12:08 pm

BTW, since this is now a separate discussion, I want to share my experience with using the 1000gm scale. I was using the American Weigh (link: http://www.americanweigh.com/product_info.php?cPath=25&products_id=338) which holds the entire pf on its platform. I would tare the scale with the empty pf/basket, then dose and reweigh. The problem I was having was small increments of change (trying to remove or add 0.1gm) caused problems. I would have to remove the pf then replace it to get the scale to notice the change which is time consuming. I find the smaller capacity scales to be more responsive to small changes. I have two of those large scales and both exhibited the same behavior.
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Postby nixter on Wed Feb 22, 2012 1:01 pm

mitch236 wrote:Easy, I just put my thumb on the lip of the basket when I hit the bar. Works perfectly most of the time.


I don't use clips and this is what I do as well. Works great.
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