# Batch brew grind sizes



## the_partisan (Feb 29, 2016)

I am curious what grind size do you think is reasonable when using something like Moccamaster? Moccamaster brews very hot, certainly hotter than any pour over and keeps high temp consistently. I am finding that with certain roasts, I get smoky/bitter hop notes even though I'm grinding very coarse (#13 at EK43S, which is >24% 1200). This is using 30g coffee to 500g water. EY on last brew was around 21%. Brew times are around 3:30-3:45.

@MWJB mentioned shop bought filter ground coffee is more like 24%1200.

I don't quite understand the brew dynamics of larger particles when doing large brews. Is it better to have a lot of larger particles or smaller, more even particles? Do the larger particles get dissolved fully? How come store bought filter coffee ground using roller mills is ground so fine?


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## MWJB (Feb 28, 2012)

I don't have a MM brewer, but I do have an MM grinder I use in the office for grinding gifted beans for French press.

I sifted this a few times and found the grind size similar to preground for filter.

You can't do anything about the evenness of particles for a given grinder, without sifting.

I guess the question is what happens when you change grind size coarser?

21% isn't that high that I'd be expecting over-extracted notes.


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## the_partisan (Feb 29, 2016)

Did you mean for illy you had 24% 1200, as I wasn't quite clear on this point?


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## MWJB (Feb 28, 2012)

the_partisan said:


> Did you mean for illy you had 24% 1200, as I wasn't quite clear on this point?


Under 400, almost nothing over 1200.

The only data I have to hand right now (at work) is 26% under 500 for the MM grinder. Can check re 400 when I get home.


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## the_partisan (Feb 29, 2016)

That one had no grind adjustment right? With the grind I'm using at #13 I only have 7% 1200. Looks vastly different.


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## MWJB (Feb 28, 2012)

the_partisan said:


> That one had no grind adjustment right? With the grind I'm using at #13 I only have 7% 1200. Looks vastly different.


That's right, no adjustment. Mind you I think MM expect you to 'set & forget' the brewer, not poke about in the basket. If you're going to agitate the slurry, I guess you might go a bit coarser.


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## the_partisan (Feb 29, 2016)

Interesting, Rao also mentions to use 20% of the coarsest grind range for batch brews, and this is what I notice most cafes using.. Does it mean with such coarse grinds you're not reaching the interior of the beans at all?


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## MWJB (Feb 28, 2012)

the_partisan said:


> Interesting, Rao also mentions to use 20% of the coarsest grind range for batch brews, and this is what I notice most cafes using.. Does it mean with such coarse grinds you're not reaching the interior of the beans at all?


Who knows? If it tastes good & normal extraction I don't see you're reaching any more/less than any other brew method/grind size.

If the flavour is off, then you may be taking too much from some parts...if this happens in a coarse grind, but not finer, then it stands to reason it's coming off larger particles (& from smaller particles if a very fine grind).

20% of what as coarsest range? Is this 20% 1000-1200 microns average, or 720-900microns average, or 560-700 (using ASTM sieves)?

Half to full gallon batch brewers will have a flat bottom basket & a wider spray head, may be a gentler delivery than the MM, which is more of a home auto drip than commercial batch brewer.

Brewing with a Melitta cone 29:467 & 41.5:660 brews, 60g/40s bloom & stir, then water poured at a constant ~3g/sec - not quite auto drip, but as close as I get to a MM brew , I'm at 12% under 400 & 66% between 400 & 1200 with the Kruve.


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## jeebsy (May 5, 2013)

the_partisan said:


> Interesting, Rao also mentions to use 20% of the coarsest grind range for batch brews, and this is what I notice most cafes using.. Does it mean with such coarse grinds you're not reaching the interior of the beans at all?


How big is your batch?

We do 120g - 130g batches in the shop and with the EK we were in the last 20% of the range. The Guatemala goes so much coarser that we're nowhere near the last 20%.


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## MWJB (Feb 28, 2012)

MWJB said:


> Under 400, almost nothing over 1200.
> 
> The only data I have to hand right now (at work) is 26% under 500 for the MM grinder. Can check re 400 when I get home.


MM grinder was 22% under 400, 77% between, 1% over 1200.

Illy preground was 24% under 400, 73% between, 3% over 1200.


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## the_partisan (Feb 29, 2016)

Your Melitta cone points to around 12% under and 22% over, where as my typical MM brew is at around #12,5 or #13. #13 is 8%1200. #12 was 8,5% above. I don't have data for #12,5 but they certainly seem quite similar. However the average particle size for the pre-ground beans seem like 50% of what I use, and this confused me.


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## MWJB (Feb 28, 2012)

ECBC (who evaluated the Moccamaster, amongst other brewers) specify an average grind size around 600um (SCAA also list this as one of 2 specs in their home brewer evaluation), the MM grinder & shop bought preground seems finer than this, more like 500um (Euro drip).

Using regular sieves my grind for the Melitta is probably nearer 750-800um. It takes me about 2:40 to 2:50 to get all the water in, then another 20-30s to dry bed. Isn't your Moccamaster a bit quicker to get the water in (less drawn out agitation)?

I'm not sure that the % over 1200 on the Kruve is the best guide, as the variance at 1 Stdev at the coarser end is usually wider than at the smaller end.


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## the_partisan (Feb 29, 2016)

Still the 90C constantly compared to something like Kalita. I also have the filter closed for first 30 seconds and stir it a few times in the beginning and about halfway into the brew. At #12.5 I already get around 21-22% EY, so I'm a bit cautious to try even going finer. Maybe as you say Kruve isn't very useful for measuring out the average grind size.

P.S: The full sieve data:


Setting BeansPAN4001200TOTALPAN40012009Kaffeverk Colombia La Fortuna1,278,960,3510,5812,00%84,69%3,31%10Kaffeverk Colombia La Fortuna1,169,010,6210,7910,75%83,50%5,75%11Kaffeverk Colombia La Fortuna0,928,61,1210,648,65%80,83%10,53%12Kaffeverk Colombia La Fortuna0,938,131,8510,918,52%74,52%16,96%13Kaffeverk Colombia La Fortuna0,776,752,349,867,81%68,46%23,73%


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## the_partisan (Feb 29, 2016)

Matt Perger was claiming that you can't reach fully interior of bean fragments that are larger than 500um. Is there any truth to this? I wonder how coarse you can go and still get a tasty, good extraction around 19-20%?


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## MWJB (Feb 28, 2012)

the_partisan said:


> Matt Perger was claiming that you can't reach fully interior of bean fragments that are larger than 500um. Is there any truth to this? I wonder how coarse you can go and still get a tasty, good extraction around 19-20%?


This seemed to be based on cupping immersions, declining temp, using extraction as a proxy for penetration. There are a few things wrong with this.

You can still normally extract drip brews with an average grind size of 900um. How do we know, given a similar level of extraction, that the >500 are not extracted if the extraction hasn't dropped?

He used a Kruve, a great tool for making comparative measurements with other Kruve users, but not ISO/ASTM standard, so hard to make statements about actual size based on historical methods.

His extractions hit ~24% immersion yield. Had he used insulated brewers & left the brews longer, even the coarser grinds would likely have reached this. There is at least another 1-5% that can be accessed by maintaining heat. This 24% is all that he could get with declining temp, static immersion. It shows no evidence of being a tangible limit based on particle size.

Declining temp immersions are hindered by temperature drop. Maintaining heat via insulation, brewing in a siphon, replacing the brew water, either by draining & refilling (similar to the AOAC official method of determining soluble solid content, which can hit 33% immersion), or by drip brewing, will push up the EY.

Static immersions like cupping & French press might also be theoretically limited by equilibrium of slurry. E.g. I find my regular steeps average 22% EY +/-2%. Let's say I brew at 1:15. 10g coffee & 150g water. If the coffee has 30% soluble solids and I get everything out, that's 3g/160g & ~1.88%TDS. 28% immersion...not going to happen in an uncovered cupping with declining temp, but you can hit it in a cezve/ibrik, even at a grind with over 500um particles. You can also hit this if you steep then drain, like in a Bonavita immersion.

Perger's example of 24% immersion suggests that there's only 25.5% available in the coffee to start with. If so, this isn't expected to be average/normal, it would be a low solubility coffee.


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## the_partisan (Feb 29, 2016)

I was just wondering if you would use whole coffee beans, or even if it was chopped in half, would it be possible to dissolve the whole soluble part of the bean eventually? What's the hard limit? Also getting all the soluble content out also seems to bring out typically undesirable flavours. I'm not sure if these flavours are inherent in the bean or can happen due to bad roasting etc though.


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## MWJB (Feb 28, 2012)

I have tried bonkers coarse, boil in a cezve, steep for another hour in a steel press, a lot of time & effort for 18% immersion 

Sanity check the bean, change it (& nothing else). Off flavours still there? If the EY changes by a % or 2, so what. A good protocol will have a span of just under 4%EY normally


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