# Grinder malfunction at finer grinds? - advice please



## DaiKonde (Oct 6, 2021)

Hi All,

Could I have some advice please?

For a while I've been making French Press coffee using my grinder at medium to coarse grind with satisfactory results.

Recently I have started making espresso switching to the fine grind settings. I noticed that when I put 17 grams of beans in, I only get 16 grams or less of powder out. Is this normal?

The finer the grind setting, the bigger the gap between weight of beans going in and powder coming out. At coarse grind settings there is almost no gap. Shaking or cleaning the grinder doesn't help. When I clean the machine after a fine grind, I do notice a lot of powder accumulating in various nooks and crannies inside the machine.

Otherwise the grind results is not noticeably uneven, and generally tastes good. The grinder is a local Japanese brand Bomak BM-250N.

I am using mainly fresh light roasted single origin beans.

My questions:

- Is it normal to have a gap between weight of beans in and powder out on?

- Will it affect taste?

- Should I clean the inside of the machine after every fine grind?

- Any solutions?

Thanks in advance for your help.


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## MediumRoastSteam (Jul 7, 2015)

DaiKonde said:


> I noticed that when I put 17 grams of beans in, I only get 16 grams or less of powder out. Is this normal?


 Yes. It's called retention. One reason why single dose grinders like the Niche Zero, or manual grinders are very popular on that aspect.

This also doesn't mean that the coffee you put in is the coffee you are putting out: On some grinders (not single dose ones) they can retain sometimes 10g of coffee, of course, depending on the grinder. Sometimes less, sometimes more. These grinds get compacted pretty hard inside the chute path, and it's virtually impossible to remove them unless you have access to the chute and the chamber.

This means that, if you put 18g in, what ends in the cup is the 10g from the previous grinding session, and 8g from the new one. Which, basically means you are drinking coffee ground the day before most of the time, even though you think you are not.

If you want to see how much your grind actually retains, you need to:

- take your grinder completely apart;
- clean it all;
- put it back together;
- weight the beans in;
- weight the beans out;

The difference, is what is trapped inside.

There are places where the coffee just fill the nooks and crannies as you say, and, in that case, it will be there and won't be "exchanged". What you need to worry about is exchange retention (i.e.: what gets ground in the burr chamber/chute and only leaves the grinder when the next session of grind pushes them out.

There's a very good explanation about retention and consistency on the Niche review:

https://coffeeequipmentreviews.files.wordpress.com/2019/03/niche-zero-review1.pdf

Page 7.

Welcome to the forum. 🙂


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## bbstrikesagain (Aug 15, 2021)

DaiKonde said:


> - Any solutions?


 I don't know if it will help, but with my hand grinder (1zpresso J-max), I add three or four drops of water to the 18g of beans and give them a good shake before putting them in the grinder. After this, grammmes in equals grammes out. Virtually zero retention. Less than 0.1g difference every time.

If I skip the drops of water, I have to shake and/or brush to get most of the grinds out. I think static is the issue, even with all metal grinder and Ti coated stainless steel burrs.

I know some people refer to spritzing with a small pump spray. For now I just add a few drops and shake it with the beans with my hand over the weighing cup. It works for me, but mine is a low speed hand grinder (30-40s usually). Maybe rapid electric grinders can press the grinds hard into nooks and crannies? Maybe spritzing won't help. If burrs are not stainless, maybe even a few drops of water is a bad idea?

Someone with an electric grinder may advise in this


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## MediumRoastSteam (Jul 7, 2015)

bbstrikesagain said:


> I don't know if it will help, but with my hand grinder (1zpresso J-max), I add three or four drops of water to the 18g of beans and give them a good shake before putting them in the grinder. After this, grammmes in equals grammes out. Virtually zero retention. Less than 0.1g difference every time.
> 
> If I skip the drops of water, I have to shake and/or brush to get most of the grinds out. I think static is the issue, even with all metal grinder and Ti coated stainless steel burrs.
> 
> ...


 There's no news here I'm afraid. This has been discussed to death, it's "proper" name is RDT (Ross droplet technique) and it's basically doing exactly what you are doing to alleviate or eliminate static.

it also works with electric grinders. However, bear in mind humidity around the burrs because, if they are box standard hardened steel burrs, they might corrode. I'm not sure about stainless steel burrs (is there such a thing?) or coated burrs. Infused to get a lot of static with my Kinu M68, and RDT did help. I used only for about a week as I feared the burrs may rust - it does happen, there's plenty of horror stories out here.

When you do this you usually spritz or add 1 or 2 droplets of water into a container, stir or shake and then put into the grinder hopper. Doing this straight into the grinder hopper won't effectively moisten the beans and you might end up getting some parts wetter than you wished for.


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## bbstrikesagain (Aug 15, 2021)

MediumRoastSteam said:


> There's no news here I'm afraid.


 There might be, in the new users' section.. ..especially if someone is struggling with retention...

I didn't know it was called RDT, but it's brilliant. Surprised you didn't mention it. Yes, I do it in the container (shot jug) I've just weighed the beans into.


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## MediumRoastSteam (Jul 7, 2015)

bbstrikesagain said:


> I didn't know it was called RDT, but it's brilliant. Surprised you didn't mention it.


 Sorry I don't understand why you say I didn't mention it when I clearly did? I'm confused.



bbstrikesagain said:


> There might be, in the new users' section.. ..especially if someone is struggling with retention


 I understand that it might be news for you or other new members, but it's no news overall. Even if you Google "coffee grinder retention drop water" you get posts back to 2015. There's a lot of information out there, and a search engine can help you with your preliminary findings.

So, let's talk about struggling with retention, as this is what really matters.

if you don't use RDT with your manual grinder and gentle give it a tap towards the end, what's the difference between what you put in versus what you get out?


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## bbstrikesagain (Aug 15, 2021)

MediumRoastSteam said:


> Sorry I don't understand why you say I didn't mention it when I clearly did? I'm confused.


 I've re-read from the top. You did NOT mention "water", "spritzing" or "RDT" at all in your otherwise helpful reply to the OP explaining retention. That's why I did, I thought it could be helpful to the OP. The guy asked for solutions, I tried to offer something that might be. Then you jump in, admonishing me with your "no news here" claim, before you finally mention and expand on the technique. Still confused? Re-read in order posted.

Sometimes in a new user section old news might well be new news...

Sometimes we might think we mentioned something, but the text search reveals we did not.



MediumRoastSteam said:


> So, let's talk about struggling with retention, as this is what really matters.
> 
> if you don't use RDT with your manual grinder and gentle give it a tap towards the end, what's the difference between what you put in versus what you get out?


 Yes, let's, here goes.

I always use what I now (thank you) know to be RDT. So first, to keep the cleaned J-Max that way, I ground a single complete *with RDT*:

*9.04g* beans in shot glass
*9.14g* with my RDT water drops (0.10g) added in the shot glass
*9.12g* after the shake, still in the shot glass (0.02g of water now on my palm)

0.00g (< 0.01g) left in shot glass after tipping beans into grinder (glass doesn't wet like a palm does, who new?)

So, let's measure out into a Sunnex shot glass with a Decent style dosing funnel on top, a happy coincidence that they play nicely...

0.00g (< 0.01g) could be knocked out of the grinder after grinding - just the lightest dusting in the glass
*9.02g* total grinds coffee after simply tipping the contents of the grinds cup, no need to shake, nothing left in it!

So, *WITH RDT*, total retention at least 0.02g, but could be as much as 0.10g if none of the water is left behind in the grinder or lost to evaporation. Even without banging or bashing, <0.1g is negligible retention.

Now, just for you, another single, this time WITHOUT any added water, *no RDT*:

*9.01g* beans into grinder
*0.79g* could only be shaken out of the grinder with a few firm knocks (try that with a big electric grinder)
*8.20g* was in the grinds catcher and had to be tapped to get it out, much of it preferred to cling to the sides
*8.97g* total grinds collected after much banging and bashing of grinder and grind catcher
*0.04g* retention

So, WITHOUT RDT we have about 0.8g (8.8%) retention unless I bash it out (a gentle tap only knocked down the first 0.2g), and whatever I do there's still 0.04g missing, presumed retention.

I'll continue to "RDT". Thanks for naming it for me. With RDT the J-Max retention is very low. Could some of it actually be gassing off? Degassed beans/grinds must weight less, and grinding smells so good there must be some loss that isn't in fact retention...

And by the way, the J-Max burrs are Titanium coated 304 stainless steel. Some of the 1zpresso range use uncoated stainless steel burrs. AFAICS most electric grinders don't use stainless steel, it's harder to machine and not as hard in use, my burrs may only survive 100kg of beans... The gold coloured burrs you see are probably Titanium Nitride coated steel alloys. Titanium Nitride is very hard and very slippery.

But absolutely, yes, there is such a thing when it comes to stainless, coated, and both!

More important though, when considering any moisture, most bearings will be chrome steel, and many parts may be plated steel. I guess folk need to be careful and sparing with any spritzing.

Right, I'm off to do something useful with the 18g I just ground...


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## MediumRoastSteam (Jul 7, 2015)

bbstrikesagain said:


> 've re-read from the top. You did NOT mention "water", "spritzing" or "RDT" at all in your otherwise helpful reply to the OP explaining retention.


 That's because I wouldn't recommend anyone to do so and, as I mentioned, and you also noted, it can rust the burrs. Been there, done that, I would not recommend unless you are 100% sure your burrs or other parts of your grinder won't rust. I, personally, don't find it very hygienic either. Humidity, water mixed with coffee grinds, room temperature&#8230; not for me.



bbstrikesagain said:


> So, WITHOUT RDT we have about 0.8g (8.8%) retention unless I bash it out (a gentle tap only knocked down the first 0.2g), and whatever I do there's still 0.04g missing, presumed retention


 Do you mean 0.4g or 0.04g? Either way, personally, I wouldn't bother with RDT. Doesn't seem worthwhile the effort, in my honest opinion. That "retention" will most likely end up in your next cup. I'd be surprised if you can taste any difference with or without it. I would consider if the issue was static and there were grinds flying all over the show during grinding - thet was the issue with my Kinu M68, drove me insane! But on a manual grinder with a lid, I'd just knock it gently at the end, and so be it, to dissipate the static.

IMVHO.



bbstrikesagain said:


> More important though, when considering any moisture, most bearings will be chrome steel, and many parts may be plated steel. I guess folk need to be careful and sparing with any spritzing.


 Exactly this! 👍👍👍


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## bbstrikesagain (Aug 15, 2021)

MediumRoastSteam said:


> Sorry I don't understand why you say I didn't mention it when I clearly did? I'm confused.





MediumRoastSteam said:


> That's because I wouldn't


 Clearly did, wouldn't, didn't? No I'm confused.



MediumRoastSteam said:


> Do you mean 0.4g or 0.04g?


 0.04g. But, and it's a big BUT, I had to work really hard to get there from what wanted to be 0.79g. For me, with a hand grinder, RDT works, always less than 0.1g retention with no effort, fluffy grounds just pour out of the catcher, saves all that bashing, and leaves nothing wet or humid. Pretty sure its was my grinder's manufacturer that recommended it!

For electrics, or other brands, maybe not so wise. For Niche, maybe not needed.


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## MediumRoastSteam (Jul 7, 2015)

bbstrikesagain said:


> Clearly did, wouldn't, didn't? No I'm confused


 I wouldn't recommend anyone to use RDT. The OP, at the time, was asking about retention.

edit: over and out.


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## DavecUK (Aug 6, 2013)




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## MWJB (Feb 28, 2012)

bbstrikesagain said:


> always less than 0.1g retention with no effort,


 I'd be sure to at least a set on 10 measurements, beans tend to weight about 0.18g each (plus or minus) so if you grind 100 doses (doesn't take that, long day to day) your variation in wholebean dose weight before grinding is likely in the region of 0.1g. For your dose to come out +/-0.1g your grinder would need to know when to add/subtract coffee.

Real dose consistency of +/-0.1g hasn't been shown to exist yet.


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## bbstrikesagain (Aug 15, 2021)

MediumRoastSteam said:


> I wouldn't recommend anyone to use RDT. The OP, at the time, was asking about retention.


 The OP was asking about a "grinder malfunction"...

I didn't recommend RDT, I asked for those with, or with knowledge of, electric grinders, to chirp in...

For my J-Max hand grinder, I will continue with what's recommended by the maker, and works, whatever you want to call it!


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## bbstrikesagain (Aug 15, 2021)

MWJB said:


> I'd be sure to at least a set on 10 measurements, beans tend to weight about 0.18g each (plus or minus) so if you grind 100 doses (doesn't take that, long day to day) your variation in wholebean dose weight before grinding is likely in the region of 0.1g. For your dose to come out +/-0.1g your grinder would need to know when to add/subtract coffee.
> 
> Real dose consistency of +/-0.1g hasn't been shown to exist yet.


 My J-Max is a hand cranked single dose grinder. It doesn't know anything.

I weigh the beans with a 200g/0.01g resolution scale, because it cost four quid and is great for weighing beans and shots. This cheapo scale matches another I have in the garage for weighing out tricky ratios of epoxy etc, but which has a too small platform and display in an awkward spot. They both cost peanuts but are consistent to +/-0.01g.

Some beans weigh less than 0.05g, some more than 0.2g. My variation in is less than 0.1g because I pull or add a small or large bean to the those I'm weighing in a shot glass. It's not rocket science. With the three house espresso blends, from the two roasters I've tried so far, there's always 2-3 varieties and a fair range in bean size. I'm sure I don't need to be so precise, but I never err by more than 0.1g. Too many digits I suppose.

Water in is a variable, usually 3-5 drops dripped in, some lost to my palm when I shake it up.

Everything solid falls through to the catch cup. Less than 0.01g can be recovered by brush, puffer and disassembly, there's negligible retention, period.

If the grinds out weigh less than grinds+water in, it's got to be because some of the moisture spritzed on the outside of the beans has transferred to surfaces from where it quickly evaporates, maybe even some out-gassing.

Are you local? I'd be glad to show off real dose consistency of +/-0.1g , but f course it doesn't mean the finished espresso is any good...


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## bbstrikesagain (Aug 15, 2021)

For all 1zpresso hand grinders:


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## MWJB (Feb 28, 2012)

bbstrikesagain said:


> Are you local? I'd be glad to show off real dose consistency of +/-0.1g , but f course it doesn't mean the finished espresso is any good...


 You could just make a video, no edits, open the bag, pour a dose of beans out, take a bean or 2 out, add a bean or two, grind it & dump the grind on to your scales. Repeat, no need to do them all in one go/day. Maybe I'll learn something (which I'm always keen to do).

I use 200g 0.01g scales for dosing too, never seen +/-0.1g consistency to 95% confidence (almost always brewing single origins, so maybe less variation in bean weight. You can do +/-0.1g 6 or 7 times out of 10). Less than +/-0.5g is good, less than +/-0.3g very good indeed.

The coffee you have is the coffee you have you can brew it consistently, you can screw it up a little as you can, but it's only as good as it is. Topping & tailing doses by 1 bean will give you absolute dose consistency with intervention. Using better coffee will make it more good


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## bbstrikesagain (Aug 15, 2021)

Just for you @MWJB, this morning's grind:






Grind was a bit fine. It was the end of one 3-bean bag, and the start of the next 2-bean bag. Two of the beans are the same origin between the bags, but roasting dates are a fortnight apart. Grinder was dialed for the older 3-bean blend - this extraction went out to 55 seconds! Experience with these coffees, I'm liking 35-45s at about 2x but have had nice brews out to a minute and ten seconds.

I got very dark chocolate, caramel, treacle toffee, pink grapefruit, and a lovely texture. Yummy.

I expect consistency will improve when I can afford to add a PID...


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