[quiff]

Disclaimer – I’m well aware this is both a first world problem, and highly unlikely to affect the quality of my coffee, I’m just interested in principle, particularly views from anyone in metrology / engineering / science fields. 

I was recently given some coffee scales, which are supposedly accurate to 0.1g. (For context, to make an espresso you use just e.g. 18g of beans, so in theory being able to tell the difference between 18g and 18.9g of beans could make a difference to flavour (see disclaimer). The scales are not hugely expensive, but are from a reputable kitchenware brand. 

I usually ‘pour’ beans in, then slow down as I close in on 18g. I noticed that if I poured to 17.Xg and then added beans slowly as I closed in on the magic number, it seemed impossible to get the scles to move in 0.1g increments – I could add say 3 beans before they changed, and then they would jump by 0.2 – 0.3g.

As a test, I then saw how many beans I could add to an empty scale before it registered anything. If I added the beans one, two, three etc at a time, I found it was possible to weigh (what turned out to be) 20+g of beans without the scales registering anything at all. I found that the scales wouldn’t register anything unless I added 7 or more beans at a time. I appreciate it’s variable, but 7 beans seems to weigh about 1g, putting each bean at more than 0.1g.

Are the scales faulty? Or am I misunderstanding what accurate to 0.1g means?      

 

           

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[hawkinspeter]

I think that’s common for

I think that’s common for most digital scales. Maybe give the scales a little tap to get it to re-weigh properly. I assume it’s something to do with a single bean not providing enough force to get the scale to update its weight, but that’s a guess.

Anyhow, you’re better off weighing the ground coffee.

[hawkinspeter]

bensynnock wrote:

bensynnock wrote:

Count 100 beans and weigh them to get a better mean weight. In fact, do that 100 times and work out the variance and standard deviation, and plot a graph of all the recorded weights. To go even further use R to generate a statistical model for the weight of beans, perhaps using other measures such as air temperature and humidity also, to enable you to determine the likely weight of any future bean counts.

That should be done for each different bean type and different roasting profiles as the moisture content will vary.

My preference is to weigh the ground coffee as that’s what I’m using to make the coffee drink. You could accurately know the exact weight of the beans, but then lose a little bit when grinding as electrostatic forces can prevent all the grounds from landing in the appropriate receptacle (I think some people use aerosolised water to control the conductivity of air).

[quiff]

I probably deserved that. Of

I probably deserved that. Of course, the follow on question is whether I can trust my scales to weigh 100 beans accurately in the first place. 

[bensynnock]

Count 100 beans and weigh
Count 100 beans and weigh them to get a better mean weight.

In fact, do that 100 times and work out the variance and standard deviation, and plot a graph of all the recorded weights. To go even further use R to generate a statistical model for the weight of beans, perhaps using other measures such as air temperature and humidity also, to enable you to determine the likely weight of any future bean counts.

[Author]

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