Dead spots midway through the shot, bitterness - Page 2

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Jake_G
Team HB

#11: Post by Jake_G »

A note on the HU burrs and dark spots...

Sorry. This is a really long post.

As Zefkir points out, the P100 (assuming HU burrs) doesn't need much PB to extract well. The burrs themselves are extremely high in uniformity (that's the name!) which means that they have one very large and narrow peak around the target particle size and then a corresponding portion of fines that increases as the main particle size decreases. The result of this distribution curve is that the packing density if the puck is noticeably less than a grinder with a wider peak (like Dan's Mythos burrs in the monolith). Less packing density means a few things, but for the nature of this conversation, it means that in order to get a longer brew time, you need to grind much finer than a grinder with a wider peak. It also means that a given dose takes up more space in the basket, but that's bot really all that relevant... this finer grind does what it is supposed to do and slows the water flow down. But it does so to the detriment of flowing evenly across the puck.

The other important aspect in play is that this puck that takes a finer grind to pull a shot in a certain amount of time also extracts much faster than a less narrow peak grinder does at a similar grind size. The recommendation to finish your shot faster is not a bad one - but it is not necessary to avoid bitters. Since the HU burrs extract quite a lot without any tricks to require a finer grind like PB, it is a reasonable strategy to simply reduce the PB duration substantially (like 5-10 seconds before switching to FB) and then coarsen the grind to still take around 30s in FB for your 36g yield. This will almost certainly extract fewer bitters and also be more uniform in extraction than what you're seeing now.

This comes back to the packing density thing. The HU burrs already require an almost talcum-fine grind to pull a normal shot duration with many coffees, and adding prolonged PB to the mix only exacerbates this property. Good coffee can be had like this, but to do that, I'd suggest actually pulling closer to 1:1 instead of 1:2. But what happens is that in order to get your shot times up, you get a puck that has a really hard time passing water evenly through it, hence the black spots.

Now. My experience with the spots is anecdotal and just my opinion, but I believe they are caused by regions of low velocity in the puck where solids (maybe fines, maybe dissolved solids, not sure which, nor if it really matters) are migrating through the puck much more slowly than the flow of espresso into the cup. If you stop the shot early enough, you will find that the spots are not there - yet. But if you cho a puck open where you stopped it early, you will see a dark region inside the puck that simply hadn't reached the bottom yet. Conversely, if you keep running the shot longer and longer, you expell the source of the dark spots from the puck and you will again have a clean bottomed puck, and this time when you cut it open, there will be no dark region within. "Success!" Someone will cry... well, maybe. I mean you got the dark stuff in the cup, and your puck will be pretty. But I'm not sure anything was fixed. And I'm not sure anything needed to be.

The other way to reduce the black spots appears to be tactics that increase the fluid velocity through the puck. If you can get a good velocity, you can push the dark region through the puck more quickly, and you can avoid spots at a lower brew ratio. There are also some grinders that just don't really make spots with normal ratios. I don't think they are better. I just think that these dark regions of stuff that accumulates and migrates through the puck tend to migrate more slowly with high uniformity burr sets, so you are more likely to see them when you grind finer and run brew ratios around 1:2 in a "normal" brew time.

Another common approach to combatting the dark spots is to run paper filters under the puck. These promote more even flow and perhaps encourage the dark regions to migrate more quickly and evenly, but I haven't dabbled in this arena personally. Our friend, astrophysicist and coffee lover/author Jonathan Gagné did a nice study on high resistance paper filters under his pucks in his crusade against dark spots and he comments that his coffee "tastes more evenly extracted" with them gone, but I have yet to ever taste a coffee and have an opinion on how evenly it was extracted. I taste things like muddled, clear, sparkling, bright, floral, sweet, chocolate, layered, etc... you know, tastes and other sensory properties of a coffee. But evenness of extraction is something I haven't found on the flavor wheel, so...

Anywho.

You're getting good advice here, but just understand that you have two tools designed for high extraction. Chances are they are both dialed in a bit too high and they are not playing nicely together. You've also got brew temperature that comes into play, as well. You can always lower your brew temp and see if bitterness fades.

Cheers!

- Jake
LMWDP #704

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spressomon

#12: Post by spressomon »

Always something new to learn, and that's a good thing :)!. Thanks for all the interesting info on HU burrs Jake!
No Espresso = Depresso

heytchap

#13: Post by heytchap »

How "full blast" is full blast?

I also see you're grinding at 0.7, which is ??? to me.

For reference, my puck screened and bottom filtered espresso is in the 1.4-1.9 range with HU in the P100. I think you're grinding way, way too finely.

iyayy

#14: Post by iyayy »

i was replicating this issue with bdb and df64 ssp mp.
probably u reach this setting in order to pull a normal 9 bar shot, since at coarser grinds the puck didnt have enough resistance, and going too tight it requires some preinfusion to work.

now im not sure how slayer PB FB works. i have preinfusion (pi) and full brew pressure.
im just using bdb manual pi at 56% (5.6bar) and my max brew pi is 8.6bar, and i'll release the button to move from preinfusion to full brew after basket saturates.
if i stop the shot once it looks pale and dial to sweetest taste, i'd end up with 1~1.2 ratio, with puck similar to yours.
note this is flat profile.
if i open up my water sprout to bleed water and pressure (mods required), i can extend it to 1.5 ratio, with cleaner puck and mellowed intensity, good since it is too intense as is without dilution but works well with milk.

what i notice to work better is to a bit dose less, reducing puck thickness by a mm to allow easier flow of water and more efficient use of the puck. but my bdb isnt slayered (yet) so i dont really have as much control.

i'd agree on coarser grinds since of i do 20s+ pi, i'll tend to hit this dark spots issue a lot more at too long pi, 10~15 is my prefered time (with my bdb). i'm using vst15g btw, and mostly on med-light and lighter.

below is example of stopping shots too early. i'd have fewer small spots (or none at all) if done well.
we're talking different machine, but if anything close to similar workflow and grind (maybe, ssp mp is considered closest in profile to HU), so ymmv.


GurgenPB (original poster)
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#15: Post by GurgenPB (original poster) »

Jake_G wrote:A note on the HU burrs and dark spots...

- Jake
Amazing! Thank you so much, love the information... I read it a few times and understand things much better now.

GurgenPB (original poster)
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#16: Post by GurgenPB (original poster) »

How "full blast" is full blast?

I also see you're grinding at 0.7, which is ??? to me.

For reference, my puck screened and bottom filtered espresso is in the 1.4-1.9 range with HU in the P100. I think you're grinding way, way too finely.
0.7 is about 52micron gap (7 microns per 0.1 tick).
That's what I'm learning from all this... it's way too fine, certainly for HU...

When you extract for lower ratios (like 1.5), am I to grind for that yield with normal brew time of ~25sec or shorter?

GurgenPB (original poster)
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#17: Post by GurgenPB (original poster) »

what i notice to work better is to a bit dose less, reducing puck thickness by a mm to allow easier flow of water and more efficient use of the puck. but my bdb isnt slayered (yet) so i dont really have as much control.

i'd agree on coarser grinds since of i do 20s+ pi, i'll tend to hit this dark spots issue a lot more at too long pi, 10~15 is my prefered time (with my bdb). i'm using vst15g btw, and mostly on med-light and lighter.
I'll try these as well... thank you.

Very interesting.

GurgenPB (original poster)
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#18: Post by GurgenPB (original poster) »

Shot a quick video, pardon the quality and the poor commentary

Thats VST 20g basket, 18:37, WDT, PorcuPress (250 needles), Puck Screen.

Would appreciate any comments you might have...