Is 32g espresso really a double? - Page 5

Beginner and pro baristas share tips and tricks for making espresso.
neutro (original poster)
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#41: Post by neutro (original poster) »

Well on one of my scales, after putting a cup of hot water on the platter, weigh actually slowly increased. With room temperature water, weigh was stable. I'm betting on temperature-driven drift of the scale due to expansion of the part on which the strain gauge is glued.

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canuckcoffeeguy
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#42: Post by canuckcoffeeguy »

DaveC wrote:for sure, in fact I expect there are a combination of factors affecting this. if it happens with hot water (which it probably will), then is could be heating+evap+trapped air. At this point each one can be eliminated to find the effect of each.

e.g.

1. Bit of Cork mat under shotglass 10mm thick = eliminates heating of load cell
2. Cold water eliminates evap
3. With cold water presumabl6 anything unaccounted for will be minute and possibly trapped air - I suspect not measurable.
Ok I did the aforementioned control tests. The video links are below. The upshot is that the biggest(and perhaps lone) factor at work here is the heating/cooling of the scale.

As has been theorized, the heating of the scale seems to cause a drop in displayed weight by 2g or more during a 1 minute span. And cool water causes a much slower and more moderate increase of 0.1 or 0.2g over the same span.

If this is accurate, with scales of this type, care should be taken to ensure brew weight measurements are noted right away, as opposed to leaving a cup on the scale, walking away for a while, and then noting the weight. In the latter case the reading could be inaccurate.

Please let me know if these control tests were sufficient. And if something was amiss in my crude methodology:

Original video (appearing to show espresso brew weight dropping 2g after sitting on scale):
https://www.youtube.com/watch?v=yAV2oU6j83c

New video showing hot water in same cup on scale:

https://www.youtube.com/watch?v=JwKdYrwuXfE

New video showing cold tap water in same cup on scale:

https://www.youtube.com/watch?v=UZLTyxrdG-A

New video showing hot water in same cup on scale(BUT insulated with a cork barrier)

https://www.youtube.com/watch?v=wBhYjwrXkOw

neutro (original poster)
Posts: 426
Joined: 10 years ago

#43: Post by neutro (original poster) »

Great work Ryan! I think your results are enlightening and pretty much settle the discussion.

Be sure to take a reading fast and/or isolate the cup from the scale when weighing hot (or very cold) liquids.

DaveC
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#44: Post by DaveC »

I agree, nice piece of work Ryan and it's clear that the major effect is heat, with evaporation possibly not measurable, or perhaps it accounted for that final 0.1g drop on cork. This is what I like to see simple home tests that clear up questions/myths I have seen around for years.....Respect 8)

Also people who weigh their shots, should consider a small cork mat for the scales. I'm certainly going to make one for mine...just cut up an old cork floor tile and laminate it.

Dave

P.S. I've done similar simple tests on that old chestnut of "CO2 trapped in the structure of the bean migrating to the surface during resting", accoutning for the CO2 given out by coffee. I believe it's another myth. When I have tested, I've not found this. "trapped" CO2 and firmly believe it's as a result of chemical processes that continue after roasting. These presumably result in the flavour changes prior to those further changes we taste as "staling".

Nate42
Posts: 1211
Joined: 11 years ago

#45: Post by Nate42 »

I did a quick test on my american weigh scale today and there was no measurable weight drop. So you guys are probably right about it being a temperature dependent scale error. Not sure if my results were due to my specific scale, or if my cup is better insulated (its a double wall stainless) .

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canuckcoffeeguy
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#46: Post by canuckcoffeeguy »

DaveC wrote:I agree, nice piece of work Ryan and it's clear that the major effect is heat, with evaporation possibly not measurable, or perhaps it accounted for that final 0.1g drop on cork. This is what I like to see simple home tests that clear up questions/myths I have seen around for years.....Respect 8)

Also people who weigh their shots, should consider a small cork mat for the scales. I'm certainly going to make one for mine...just cut up an old cork floor tile and laminate it.

Dave

P.S. I've done similar simple tests on that old chestnut of "CO2 trapped in the structure of the bean migrating to the surface during resting", accoutning for the CO2 given out by coffee. I believe it's another myth. When I have tested, I've not found this. "trapped" CO2 and firmly believe it's as a result of chemical processes that continue after roasting. These presumably result in the flavour changes prior to those further changes we taste as "staling".
Thanks Dave. Mystery solved. You provided the blueprint for testing. Cheers for your help. Good to know that some scales can be affected by temperature. But it's understandable, since they weren't designed for weighing espresso. Mine is frequently advertised for weighing jewelry.
neutro wrote:Great work Ryan! I think your results are enlightening and pretty much settle the discussion.

Be sure to take a reading fast and/or isolate the cup from the scale when weighing hot (or very cold) liquids.
Cheers!

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