# Zenith 65E reliability - dose variation explored (This is a LONG post)



## bongo (Apr 20, 2014)

Eureka Zenith 65E

Home reliability testing

Mr. Bongo, 2015.
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Background

Over the last week a few people, myself included, have read and discussed the variation in dosage mass of the Eureka Zenith 65E (E.65E). I ordered a new E.65E which arrived yesterday. The joy of my delivery is in the thread "What did the Postie bring you today?" post #3523.

What I wanted to know was what is the variation in dose on this well recommended and well rated, timed, on demand, grinder.

Method

I spent approximately 45 minutes sorting out the grind settings such that my approximate dose was ~15g, and the grind was such that it took 25-30 seconds to extract ~30g of coffee through my Expobar DB. This took about 200g of beans to achieve. The beans used are in pic 1 below:






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Before starting the main test on the grinder, I wanted to see how reliable my scales were. So I weighted my 18g VST basket 21 times. Each time I turned the scales of, turned the scales on, waited for them to zero, then weighed the basket (see pics 2 and 3).






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The 18g VST basket weighed in at an average of 26.29g with a standard deviation of 0.01g (range 26.27-26.31g). While I don't have any ways to validate the measure, for reliability purposes, I have to say I was impressed, as these scales cost about £5 delivered from eBay.


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## bongo (Apr 20, 2014)

I then ground 21 shots of coffee and recorded the total weight of grounds and basket (see pic 4). Each time I emptied the basket and wiped it free of grounds before grinding the next shot at taking the weight of the shot and basket combined.








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After the first 3-5 shots, the hopper was empty and I had to load with a fresh bag of beans. This caused over a 1g average drop in dose weight. As such, I removed the first 5 measures from the data set. Unfortunately I didn't record them before saving the file I was using and thus lost the data.

However, the raw data from the remaining shots is shown below:






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## bongo (Apr 20, 2014)

I calculated the coffee weight by subtracting the average Basket weight (average of 1st column) from the overall WT (column 2). I then calculated the mean difference of the Coffee WT to the Mean Coffee WT (value from column 4 minus average of column 3). The graph below shows the variation quite nicely:








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This shows the actual coffee WT against the mean weight (dotted orange/red line) of each shot (14.14g).

I added a trend line which shows how over time, as the hopper emptied, the weight gradually increased.


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## 4085 (Nov 23, 2012)

Until your burrs are properly seasoned, your results will not be meaningful


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## bongo (Apr 20, 2014)

I then looked at the variation about the average shot weight in more detail plotting a for of Bland and Altman (1986) plot:








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This indicates that the variation in shot weight doesn't vary from 'normal'. I.e., all the points on the graph fall within the expected variance which is indicated by the upper and lower lines. These indicate plus and minus 1.96 x Standard deviation.


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## bongo (Apr 20, 2014)

dfk41 said:


> Until your burrs are properly seasoned, your results will not be meaningful


Thanks for interrupting, but everything is meaningful. as when this exact method is followed in a month, 2 months, a year etc we can all see what difference if any 'seasoning' the burrs actually makes.


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## bongo (Apr 20, 2014)

What the graph does indicate is that with every shot pulled (i.e., as the hopper emptied) the shot weight increased with a moderate effect R(sqrd) = .38

So contrary to what I have read, where it has been stated that more beans in the hopped would 'push' the beans through better. Actually, less beans in the hopper increases the weight of the shot. This could be due to less pressure from the weight of beans allowed the 'flow' of beans into the burrs to improve slightly.


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## Eyedee (Sep 13, 2010)

Doesn't the fact that as the weight of beans on the burrs gets lighter, the actual coffee ground gets heavier, appear to defy logic.

I would have expected more weight on the burrs would result in more ground weight.

Ian


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## NickdeBug (Jan 18, 2015)

Thanks bongo

Really interesting stuff. You could round it off with a nice Pearson's chi-squared test to check the statistical significance of your data set.

Did you "season" the burrs first? I understand that grind speed and particle distribution will change over time as they settle in.

edit - ignore last bit, just seen your response


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## 4085 (Nov 23, 2012)

bongo said:


> Thanks for interrupting, but everything is meaningful. as when this exact method is followed in a month, we can all see what difference if any 'seasoning' the burrs actually makes.


bongo, you woffling mate. A month does not mean anything in the life of a burr set. The only thing that is meaningful is the weight of coffee beans going through. I predict in a months time, you will see different results....so what? Thats the equivalent of hopping the 100 metres and in a months time, using 2 legs and jumping. What do you expect the data to show since you KNOW your burrs are not bedded in?

Anyway, go back and I hope you enjoy playing!


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## bongo (Apr 20, 2014)

NickdeBug said:


> You could round it off with a nice Pearson's chi-squared test to check the statistical significance of your data set.


Will have a look at this later, I've got to run to a meeting now, and have wasted all my prep time this morning playing with this blooming grinder! ha


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## bongo (Apr 20, 2014)

dfk41 said:


> bongo, you woffling mate. A month does not mean anything in the life of a burr set. The only thing that is meaningful is the weight of coffee beans going through. I predict in a months time, you will see different results....so what? Thats the equivalent of hopping the 100 metres and in a months time, using 2 legs and jumping. What do you expect the data to show since you KNOW your burrs are not bedded in?
> 
> Anyway, go back and I hope you enjoy playing!


dfk41...

If you've a better way of drawing a conclusion about any effect of seasoning burrs and how to test the difference then I'm all ears.

You otherwise fail to make any clear argument or point....

I've only done this as a point of interest.


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## bongo (Apr 20, 2014)

Eyedee said:


> ...
> 
> I would have expected more weight on the burrs would result in more ground weight.


Indeed. This is the common belief / understanding - or perhaps following these results the common mis-understanding...


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## NickdeBug (Jan 18, 2015)

Bongo, stick with it despite criticism.

It's good to see some proper science being applied rather than the usual rush of anecdotal "evidence"


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## 4085 (Nov 23, 2012)

bongo, I am not knocking your efforts mate, but I am saying it is a bit pointless. There will be variations in the manufacture of all burr sets so you are not really comparing like to like. And even so, if you charted these tests right the way through the life of the burrs then you will constantly note changes in performance as they degrade or blunt. It is intereresting but I cannot see what you are going to conclude from it all, other than until they are bedded in, results vary!


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## bongo (Apr 20, 2014)

dfk41 said:


> if you charted these tests right the way through the life of the burrs then you will constantly note changes in performance as they degrade or blunt. It is intereresting but I cannot see what you are going to conclude from it all, other than until they are bedded in, results vary!


Well I guess for some people this IS the point. i.e., What is the sort of variation expected on this machine, on a new burr set?

This will let people know if they want to rely on the timer or continue measuring the bean weight. I.e., grinding a weight of beans rather than grinding beans by time.

Maybe people will decide they don't like the variation seen and so would prefer a different grinder. Maybe up the anti to an EK43....who knows.


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## Eyedee (Sep 13, 2010)

Surely the first thing we have discovered is that more weight in the hopper does not necessarily mean more weight in the PF, quite the reverse, unless of course this changes when the burrs are bedded in.

Ian


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## bongo (Apr 20, 2014)

indeed.

And another thing to potentially follow up on.


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## bongo (Apr 20, 2014)

It also indicated that on changing the beans, the dose weight changes by a gram or so (unpublished data).

So when changing to fresher / different beans, a small adjustment maybe needed to maintain consistency in dose weight.

Overall, it simply says that the E.65E grinder (when new) is reliable at pulling the same weight of beans and this is irrespective of weight of beans in the hopper (based on 0-250g in the hopper).


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## 4085 (Nov 23, 2012)

Not trying to throw a spanner in the works, but my coffee setup is in a breakfast room, next to a window which gets the sun from 9am in summer till about 4, and also next to the central heating boiler. My beans need constant adjustments due to the humidity, heat generated etc, meaning that that has nothing to do with the grinder but still needing adjustments anyway.


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## bongo (Apr 20, 2014)

dfk41 said:


> Not trying to throw a spanner in the works, but my coffee setup is in a breakfast room, next to a window which gets the sun from 9am in summer till about 4, and also next to the central heating boiler. My beans need constant adjustments due to the humidity, heat generated etc, meaning that that has nothing to do with the grinder but still needing adjustments anyway.


Yawns... pats mouth... looks straight past the bloke and shouts "next please"....


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## 4085 (Nov 23, 2012)

I love it when people do this! You play away mate and tell us all how it is going. I am sure there are lots of interested parties. You are right. I will bow out, after all, what can I possibly hope to offer this thread if I dare disagree with you?


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## Daveteauk (Jan 4, 2015)

Hi Bongo, I hope you're enjoying your new toy. I'm very happy with your old SJ. I'm fairly new to all this but, as an R&D engineer, wonder why if xxg of beans go unto the hopper/mouth of the grinder, and all are ground, why on earth will the ground weight be different, no matter whether the beans go through under their own weight or are 'pushed' through with a tamper on top or even the weight of other beans on top. If x amount of beans go in, then surely the same weight of grinds come out - or am I missing something?


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## jeebsy (May 5, 2013)

It grinds by time, not by weight.


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## Daveteauk (Jan 4, 2015)

There's a lot of talk about new burrs needing to be 'seasoned'. Why is this, and how long would it take in the home environment? Maybe a day in Costa etc, but in the home, where one may make c2 coffees a day (like myself), how long would that take? I bought Bongos Mazzer SJ and he says he makes the same amount as myself, so after 9 months, are they seasoned yet?


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## Daveteauk (Jan 4, 2015)

jeebsy said:


> It grinds by time, not by weight.


@jeebsy - who are you answering here mate?


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## 4085 (Nov 23, 2012)

burrs vary but around 10 kg would normally get you there. If in doubt, try and get some stale coffee from any local roasters and put it through. If you do that, start off with your burrs set to very coarse and work your way back towards finer. The amount of weight in the hopper pushing the beans will also have something to do with it. There are so many variables.

Bongo, have you tried single dosing and forgetting the timer in favour of weight in and out with the usual lens hod mod?


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## Dylan (Dec 5, 2011)

I dose my beans into the throat of the grinder, then tamper on top. If I put weight on the tamper I see the expected increase in output weight as opposed to putting no weight on it. Your results show the opposite of this, which poses the question of why...


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## jeebsy (May 5, 2013)

Daveteauk said:


> @jeebsy - who are you answering here mate?


You


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## CallumT (Aug 23, 2013)

At first I was all for this but after reading more in-depth the results aren't really that useful, regardless of the burr condition your main issue is temp. variance just like the morning dial in in most shop environments. also if you were dialing in you would be changing grind setting and any change in grind setting changes grind speed; grinders usually can grind more bean mass in a given time at a courser setting and less bean mass at a finer setting.

The more useful data is same grind size, same procedure for first drink in a morning and keep hopper with same amount of coffee in there. Basically try to take adjustments out of the data as well as temp variance within the grind chamber.


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## bongo (Apr 20, 2014)

Time & weight of beans versus output:

This is my breakdown from today's 'fun'.

The question asked is :why, with more weight of beans in the hopper did the output decrease. Or conversely, when the weight of beans decreased, the output increased?

To clarify by weight of beans, I am referring to weight of beans in the hopper.

My best guestimate is that increased weight of beans, adds to friction/resistance against movement. Considering the time taken to grind the weight was unchanged, as the weight of beans in the hopper decreased the beans could move more freely into the burrs and consequently gave a greater output in that time frame (which incidentally was 9.5 seconds)

Why was this different for Dylan?

Well when grinding a specific weight of beans the added resistance/block offered by the tamper means nothing escapes compared to no weight/ block. Here, I think the output is effected by the 'block' rather than the 'weight' offered by the tamper.

It is unreasonable (IMO) to suggest that when putting 18g and only 18g through a grinder, which then runs until all 18g are ground, that adding weight makes only difference to the output. Blocking the escape of beans as they fire out of the mouth of the grinder is the only thought I can offer on this.

It is worth nothing that during my testing, the hopper never ran empty.

Starting from trial 5/6 the weight in the hopper decreased with every shot ground. This led to a relatively linear increase in output for the same duration of grinding.

Had I continued until empty, perhaps the relationship would have been more parabolic than linear, i.e., when the hopper was full (250g) - output was low. When hopper was half full (100-150g) output was at max. Had I continued until less weight, say 25-50g (for arguments sake) was in the hopper, maybe the output would have backed off again. This I do not know.


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## froggystyle (Oct 30, 2013)

I admire your dedication, me, i just grind out till i get my required dose then make a coffee!


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## Dylan (Dec 5, 2011)

bongo said:


> Why was this different for Dylan?
> 
> Well when grinding a specific weight of beans the added resistance/block offered by the tamper means nothing escapes compared to no weight/ block. Here, I think the output is effected by the 'block' rather than the 'weight' offered by the tamper.
> 
> It is unreasonable (IMO) to suggest that when putting 18g and only 18g through a grinder, which then runs until all 18g are ground, that adding weight makes only difference to the output. Blocking the escape of beans as they fire out of the mouth of the grinder is the only thought I can offer on this.


I would guess that it has something to do with the block also. To clarify however, if I put weight on the tamper the output weight is greater than if I just let the tamper rest.

I'm going to double check these assertions and report back when I have some more beans (only just ground a whole kg of stales from foundry through >_


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## coffeechap (Apr 5, 2012)

Ok some figures for you as I was bored

100 grams of beans in borosilicate glass tube hopper,

Grinder - Elektra nino

Beans - light roast

First 5 shots without my additional 2 kg weight that aids consistency at lower levels beans.1.5 second grind time.









1 -14.6 grams

2 -13.8

3- 14.4

4- 14.6

5- 14.2

2 kg weight added on top of the beans 100 grams 1.5 seconds time









1. 18.4

2. 18.5

3. 18.6

4. 18.4

5. 18.3

My conclusions although very basic are weight of bean improves the performance of OD grinders, I appreciate that the steel weight does no react like beans in a hopper and does driver the beans straight down into the burrs, but it stops popcorning, improves grind consistency and improves the variance in shot after shot output.


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## Dylan (Dec 5, 2011)

Ah, no need for me to test it out it seems, thats clear enough that a solid downward weight increases yeild.


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## NickdeBug (Jan 18, 2015)

what isn't clear is the forces at play with a full hopper. As bongo mentions, the friction between beans and the outward force are all going to impact flow rate.

I have just finished a study looking at improving flow rate of seed through a standard drill, and the relationship of volume to flow rate is definitely not linear. It comes down to the flowability of the beans themselves. To give you an example, if you scale this problem up, using grain with poor flow properties can actually collapse a grain silo do the the horizontal pressures imparted. The baffle, or flow aid that you find in many hoppers is to prevent the column formation that exacerbates this effect.

CC's straight weight and cylinder is idea to prevent this occurring.

If you want to do a little experiment, get a kitchen funnel and try pouring 100g of old beans through it. They should go through fairly easily (provided the orifice is big enough!). Now add about 10ml of water to the beans (assuming that you dont want to use them) and try again. If you do this you should see the quite dramatic difference that changing one factor can produce. It then seems reasonable that other factors such as temp and humidity, and even the age of the beans are also going to have effects.

I still like Bongo's study. If he can keep everything else the same and just look at the ageing of the burrs it will give a useful indication as to how long it takes to settle.


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## bongo (Apr 20, 2014)

I will come to my own defence, and as mentioned by Dylan, when I have mentioned adding / varying weight i.e., adding the tamper not just bean weight, I did not scale up enough for what a number of you are talking about.. i.e., adding a 2kg weight, or pressing down on the tamper. Didn't even consider those as options.

How small was the box within which I was thinking....! ha

Has made for an interesting chat though for some of us. Good to see other people thinking about this. Love the silo example too. Well said NDB


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## coffeechap (Apr 5, 2012)

bongo said:


> I will come to my own defence, and as mentioned by Dylan, when I have mentioned adding / varying weight i.e., adding the tamper not just bean weight, I did not scale up enough for what a number of you are talking about.. i.e., adding a 2kg weight, or pressing down on the tamper. Didn't even consider those as options.
> 
> How small was the box within which I was thinking....! ha
> 
> Has made for an interesting chat though for some of us. Good to see other people thinking about this. Love the silo example too. Well said NDB


this stuff is interesting and only serves to better the understanding that we have about grinders. that same grinder that I have used to demonstrate my findings (albeit in a less scientific way and only over a few shots) was a completed pain in the arse with regard to static and the chute clogging, which happens when no weight is applied (this issue is exacerbated due to a missing flap at the exit point of the burr chamber), however when applying weight to the beans in the tube, all of the retention and static issues dissappeared


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## Sean (Jun 20, 2014)

As a 65E owner, I have no idea what to make of this. I don't think it will affect my life and I'm not sure I can use any of the data.

My use of the grinder is to set it up 'about right' and see what happens. I enjoy the chase and for me, some of the enjoyment is lost by breaking it down and over-thinking things. I accept that others enjoy the more scientific approach as I do with other interests or hobbies. And to them this may be more useful. Also as Dave says, it can only add to the knowledge base here, which is never a bad thing. And it's always important to encourage input and involvement. So thanks for the time and effort.


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## DoubleShot (Apr 23, 2014)

bongo said:


> Yawns... pats mouth... looks straight past the bloke and shouts "next please"....


Too funny!


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## Beanaholic (Feb 2, 2015)

bongo said:


> Yawns... pats mouth... looks straight past the bloke and shouts "next please"....


This is was a tad unfair I feel. You are being a 'sheldon' not a 'Leonard'. Humidity, temp. and bean variation can make a significant difference. Did you mix the beans before placing in the hopper? If not, your first grinds will be the least dense beans, and they will get progressively denser as you go on. The heaviest beans will have sunk to the bottom of the bag, and hence will be at the top of the hopper. Also, the heat from the grinding may be 'drying out' the beans above. Most likely rubbish, but these factors need to be eliminated before the data becomes truly meaningful.

admire your spirit though


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## bongo (Apr 20, 2014)

Not for a home situation.

This design was representative of how reliable the grinder would perform by simply using a new bag of beans and in a home, with its normal variation in temp and humidity which can not be controlled.

While the intention of the comments may be relevant for a lab based condition, again this was not a lab.

there is also a far better way to present the points.


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## bongo (Apr 20, 2014)

So infact the inverse is quite the point. If the reliability on thelab was perfect. Zero variation in weight of grind/output, what does that mean in the kitchen orcoffee shop?

Nothing. Thats the answer.


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## paul whu (Sep 25, 2014)

dfk41 said:


> Not trying to throw a spanner in the works, but my coffee setup is in a breakfast room, next to a window which gets the sun from 9am in summer till about 4, and also next to the central heating boiler. My beans need constant adjustments due to the humidity, heat generated etc, meaning that that has nothing to do with the grinder but still needing adjustments anyway.


Can you either move the grinder or draw the curtains?!! Maybe relocate the boiler?


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## 4085 (Nov 23, 2012)

paul whu said:


> Can you either move the grinder or draw the curtains?!! Maybe relocate the boiler?


I do not need to do either, because I do not give a tinkers cuss about microscopic variations like this


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## hotmetal (Oct 31, 2013)

I like the fact that someone with the same grinder as me had taken the time to figure all this out. I have neither the time nor the patience, nor do I have a sufficient grasp of statistical methodology. I'm interested to see what comes out of these trials. My experience with the 65e so far is that, for a given bean, once dialed in, relying on the timer gives me 18g +/- 0.3g in 10". This is good enough for me given that if I'm in a weighing mood I can strike off/top up if needed. Most of the time I'm not that concerned with 1/4g though, so it's good to know that the timer is accurate enough, assuming there is a reasonable quantity of beans in the hopper. It's good to have this confirmed by someone who had taken the time to measure. I accept that other factors such as humidity, temperature and age of bean might have s significant effect, but ceteris paribus it's a worthwhile exercise I think.


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## funinacup (Aug 30, 2010)

bongo said:


> So contrary to what I have read, where it has been stated that more beans in the hopped would 'push' the beans through better. Actually, less beans in the hopper increases the weight of the shot.


Did you make & time any espresso shots from these grinds?

Less weight in hopper = coarser grind & higher dose.

Full hopper & chosen grind setting = consistent dose until hopper depletes by 2/3 to 1/2 full.


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## bongo (Apr 20, 2014)

funinacup said:


> Did you make & time any espresso shots from these grinds?


no.

it all went in the bin. If i did, someone would only complain that the variation in my timeline between starting and stopping the flow of water would have made the results meaningless, or that i didnt control my tamping pressure.... (You guys know who you are







)

It would be an interesting though, i.e., particle size variation and how this coincides with change in ouput and input weight varietion...

from memory there was a discussion on here in the general grinders section where they were going to look at variation across a couple of grinders... I dont have the equipment for that.


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## bongo (Apr 20, 2014)

funinacup said:


> Less weight in hopper = coarser grind & higher dose.
> 
> Full hopper & chosen grind setting = consistent dose until hopper depletes by 2/3 to 1/2 full.


Is this a suggestion or something you know or have read somewhere? The latter part is the bit I'm more interested in atm, as this 'rule' would surely depend on the size of the hopper....

There re are just so, many variables....


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## funinacup (Aug 30, 2010)

Something I experience everyday.


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## migralda (Nov 8, 2012)

Those long winter nights must fly bye In Bongo's house!


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## ThePeginator (Dec 17, 2019)

coffeechap said:


> this stuff is interesting and only serves to better the understanding that we have about grinders. that same grinder that I have used to demonstrate my findings (albeit in a less scientific way and only over a few shots) was a completed pain in the arse with regard to static and the chute clogging, which happens when no weight is applied (this issue is exacerbated due to a missing flap at the exit point of the burr chamber), however when applying weight to the beans in the tube, all of the retention and static issues dissappeared


I've just picked up a Chimbali Magnum OD (I'm really only in the absolute infancy of all of this) but it has the same issue you mention of ground coffee getting stuck in the chute, and having to tab the chute or wiggle the grinder to get it out.

Is it possible having weight on the beans above could help/eliminate this?

Sent from my iPhone using Tapatalk


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