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Why do burr grinders vary in grind size

rchamlen

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Dec 10, 2021
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Minnesota, USA
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Nube here - so pardon if this has been discussed numerous times in the past (I did not easily find any previous discussion....)

After many years of wanting one, I finally obtained a reasonable quality espresso machine (a Rancilio Silvia) .... and so am finally able to reasonably observe the effect of varying grind size. I am (have been) well aware of the fact that a good (i.e. expensive) grinder is considered really- really needed - mostly due to consistency in grind - but have not had the hands-on experience to understand *why*. I.e. - just what is varying in the lesser grinders to create that variability in grind.

For example, I have an old (but very, very seldom used) Krupps burr grinder that I decided to use to first experiment with this Silvia machine. A couple things I notice - on the finer settings of the machine, there is a one-setting difference between shots pulled too fast (like 10 seconds), versus shots pulled too slow (like a minute or so). Occasionally (like this morning), I go go grind and pull a shot - and the silvia is totally unable to push anything but a few drops of water through the puck. This has happened several times (without my having changed the grind setting on the mill) .... and it seems like it is clogged (or backed up) at the outlet of the grinder????? In either case, if I go in with a fine tool, I am able to work out a significant amount of grinds from the outlet - and after that the grind seems ok, and the silvia is able easily to push water through the puck.

So, again, I think in terms of "why" something happens. Does anyone here understand
1) whether/why a partially clogged mill outlet can lead to such a fine grind that the espresso machine can not extract the puck?
2) do all machines, including the expensive ones, suffer from this "outlet clogging", and do they all just require periodic un-clogging????
3) with the lesser machines, is there just some hard-to-pin down variation in the grind (day to day? bean to bean? roast to roast?) that makes it hard to be consistent in shot qualities?

Please, just for the sake of argument here (and so we do not go off on a whole different tangent), assume that I am doing "ok" in terms of consistency of quantity of grounds, and leveling and tamping technique, and that much of the variation I am seeing is due to grind variation (that may not be a perfect description of my state - but I think is good enough to try to answer this question as posed.....)

Thanks all.
 
A capable grinder will not only grind fine enough, but will do so consistently AND have a good/usable range in that finer zone. Lots of grinders will go fine enough, but the particle size will vary greatly. Espresso specific grinders are designed/built to higher tolerances so the slightest changes can be made to dial different coffees in and will offer that level of accuracy repeatedly. Keep in mind that lots of variables affect espresso such as the coffee being used (varies according to origin, process method, roast development, age post roast, storage, etc.), ambient temp/humidity, machine functionality such as brew pressure/volume, dose weight, tamp to some degree, etc. It doesn't have to be super involved to get great/consistent results, but there are things that must be focused on to get where you want the end result to be.
 
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Yeah - I am aware of the variables that affect espresso. I *think* I am being pretty consistent in terms of amount of grounds and tamping. But *something* is happening to create some significant variation. For example, this morning, with the grinder set on the same grind setting, the first shot was ok (but just a tad faster than I would have wanted), but the second shot flowed very slowly, and took something like 1 1/2 minutes to extract. For now, I can say I used the same volume (not weight) of coffee, and tamped the same, so I am putting it up to variation in the grind (not variable particle size in the same puck, but much finer particles in the second grind).

Like I said, I am seeing that the grinder will get clogged in the outlet, and if I go in manually and remove the stuff in the outlet chute, then things go back to "normal" .... hence my question on whether it is common, even with the more expensive grinders, for the outlet chute to get clogged, leading to (I am guessing) slower throughput and much finer grind.... ????

Nice to know though that the higher level grinders have a more useful range at the finer grinds (mine certainly does not .... and btw it is a Braun grinder, not a Krupps - sorry about that.....)
 
Yeah - I am aware of the variables that affect espresso. I *think* I am being pretty consistent in terms of amount of grounds and tamping. But *something* is happening to create some significant variation. For example, this morning, with the grinder set on the same grind setting, the first shot was ok (but just a tad faster than I would have wanted), but the second shot flowed very slowly, and took something like 1 1/2 minutes to extract. For now, I can say I used the same volume (not weight) of coffee, and tamped the same, so I am putting it up to variation in the grind (not variable particle size in the same puck, but much finer particles in the second grind).

Like I said, I am seeing that the grinder will get clogged in the outlet, and if I go in manually and remove the stuff in the outlet chute, then things go back to "normal" .... hence my question on whether it is common, even with the more expensive grinders, for the outlet chute to get clogged, leading to (I am guessing) slower throughput and much finer grind.... ????

Nice to know though that the higher level grinders have a more useful range at the finer grinds (mine certainly does not .... and btw it is a Braun grinder, not a Krupps - sorry about that.....)
First extraction being a bit different is usually due to stale retention from the previous use. Then by the 2nd extraction you have fresh ground that will behave as you expect. When I use my electric I purposely cause the flow to back up into the chute a bit to give me very well controlled output. As in holding a few fingers in front of it to let the coffee buildup instead of shooting out into the doser. I get better consistency doing that and have with multiple grinders. Gives a more 'homogenous' grind quality, whereas when I haven't done that I have to grind a bit finer to get the same end result. Every grinder will be a bit different and even a 5% change in humidity can affect fineness needed to keep things dialed in.

My electric never comes close to clogging and can easily crank out Turkish fine powder if needed, but it also consumes close to 800 watts in the process. My actual every day preference is a hand grinder that simply gives me world class grind quality, no retention, no waste of electricity and isn't affected by temp/humidity the way electrics have been for me over the years. The grind range is enormous, truly stepless in a very positive way and can be adjusted in microns for the most miniscule changes possibly needed and most importantly that setting never drifts.
 
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slight resurrection of this thread.... Last night I had a chance to take apart and clean my burr grinder. It is not really designed to be taken apart, but, a little prying here and there did the job....

I was surprised by the amount of fine powder caked up all over the place, in places occluding almost have of the space that grounds are meant to flow through. By caked, I mean quite hard - it took hard implements (mostly toothpicks) to dislodge the stuff and quite a bit of banging on the thing to get the now loosened stuff out of the grind path.

Is it typical that a burr grinder needs to be thoroughly cleaned regularly? If so, how often (say for daily personal use)? If the answer is "yes", then I guess it makes sense to look for a grinder that is expressly (no pun intended) designed to be taken apart easily....
 
slight resurrection of this thread.... Last night I had a chance to take apart and clean my burr grinder. It is not really designed to be taken apart, but, a little prying here and there did the job....

I was surprised by the amount of fine powder caked up all over the place, in places occluding almost have of the space that grounds are meant to flow through. By caked, I mean quite hard - it took hard implements (mostly toothpicks) to dislodge the stuff and quite a bit of banging on the thing to get the now loosened stuff out of the grind path.

Is it typical that a burr grinder needs to be thoroughly cleaned regularly? If so, how often (say for daily personal use)? If the answer is "yes", then I guess it makes sense to look for a grinder that is expressly (no pun intended) designed to be taken apart easily....
The practice of doing so will maximize freshness, etc. Interval depends on the coffees you like, mainly roast level as that somewhat determines surface oils, environment as humidity causes retention at times, etc. Whether I use the electric or hand grinder I give them a quick brush/vacuum after every daily use. Not as in tearing them down, but have made a piece to attach to my vacuum to really get down into the burr chamber to remove anything left behind. I still tear them down a few times yearly just to wipe out any oily residue, dust, etc. and there really isn't much to bother with after doing the daily preventive maintenance.
 
I myself do not make espresso. Way steep learning curve. But I am reading about it and learning from videos.

In response to your post I found this video, which I hope addresses at least some of the points you raise.

 
So apparently, the grind size needs to be adjusted for new beans, for aged beans, or changing how much coffee you are grinding. Other things too, like changes in how you tamp the grounds. So grind size seems to be a commonly adjusted thing. Hope this all helps.
 
So apparently, the grind size needs to be adjusted for new beans, for aged beans, or changing how much coffee you are grinding. Other things too, like changes in how you tamp the grounds. So grind size seems to be a commonly adjusted thing. Hope this all helps.
As well as roast level, bean density, process method, ambient temp and especially humidity... also throw in watching for a full moon, etc. Espresso is never really mastered as the variables are always changing regardless of the thought/effort applied. Personally wouldn't get too caught up in lame 'influencer' (a.k.a. BS artists) videos as most is done for monetary reasons.
 
Well, just by looking at the burrs and their configuration inside a grinder, you'd know this is 100% true: you can only control MAXIMUM size, not MINIMUM size, with it! If you want to control both to make grind "consistent", use sieves that match your maximum size and let all smaller grinds go.
For example, if you want your grind to be consistent 400 microns (+0, -50), you can use a 400 micron sieve first to let all particles equal or smaller than 400 go. You can then let them pass a 350 micron sieve to get rid of anything smaller than 350 microns. Now everything inside your sieve will be between 350 and 400 microns.
But if you want everything to be exact 400 microns, you simply can't do it even you spend $1M on a grinder.
 
Well, just by looking at the burrs and their configuration inside a grinder, you'd know this is 100% true: you can only control MAXIMUM size, not MINIMUM size, with it! If you want to control both to make grind "consistent", use sieves that match your maximum size and let all smaller grinds go.
For example, if you want your grind to be consistent 400 microns (+0, -50), you can use a 400 micron sieve first to let all particles equal or smaller than 400 go. You can then let them pass a 350 micron sieve to get rid of anything smaller than 350 microns. Now everything inside your sieve will be between 350 and 400 microns.
But if you want everything to be exact 400 microns, you simply can't do it even you spend $1M on a grinder.

You are correct. When consulting with new coffee shop owners, they are always shocked at the cost of grinders. The more expensive the grinder / the less variance between large/small particle sizes (in general).
 
I wonder if there is any grinder comparison test for gradations, D-values and uniformity coefficients. For example, set all grinders to grind 400 microns. Then use a 400 micron sieve to measure how much in percentage will pass through it. The higher the percentage, the worse the grinder. And use the test results to set the price (guess how cheap those expensive grinders will become...)
 
As well as roast level, bean density, process method, ambient temp and especially humidity... also throw in watching for a full moon, etc. Espresso is never really mastered as the variables are always changing regardless of the thought/effort applied. Personally wouldn't get too caught up in lame 'influencer' (a.k.a. BS artists) videos as most is done for monetary reasons.
A discussion for a different venue, but suffice it to say I don't trust non-monetary motivations.
 
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