Dark roast coffee requiring much finer grind than medium roast?

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#1: Post by alexanders5700 »

Hi all, long time lurker,

I've looked over this forum, and others, and have not found much info on my problem.

(newbie here, 4 weeks in to the hobby. Profitec Pro 700 (great used deal), Niche Zero, VST 18g basket, Jack leveler)

I've been so far getting roasted beans from a local cafe (that also sells/ships online), medium roast (no oils on beans).
Going well, got it dialed in to 18g in, 36 out, 200F, 28 seconds.
Tried 3 different Medium roasts, got them all dialed in to the same as above. Grinder always in the 16/18 range on my NZ.

For fun, I wanted to try a dark roast, as I want something that cuts through latte milk, and strong enough to water down for Americano.

I got the Starbucks Verona (Dark roast) (best before indicates 5 months in the future).

So the beans are much much darker, bigger, less dense, oily sheen (as expected).

Ok, so step one, reduce grind setting on NZ from the 16/18 that it's been for Medium roasts, down to 20. Reduce temp to 198F.
18g into NZ, grind, then try to get into the VST 18g basket. IMPOSSIBLE. Way way too much. Dark roast is too fluffy. Huge mound. Falls off VST basket when I take the NZ cup out of the basket. Lots of static (never seen that with the Medium roasts).
I lose .7/.8g to the sink. WDT, Jack leveler. Pull shot.
Shot time: 9 seconds (yes 9 !!!)

Damn. OK, put grind back to 17/18.
Shot time: 10 seconds

OK... put grind to 14.
Shot time: 10 seconds

OK again.. put grind to 10
Shot time: 10 seconds. What the hell

Finally last shot before I have to go to work, out of desperation, put grind at 7/8.
Shot time: 22 seconds (at least it's making an impact)

I just don't understand. Literally the day before, 24 hours, I had medium roast at grind setting 17/18, 18g, at 28 seconds.

Question: has anyone seen something like this themselves? I mean dark beans should require coarser grinds, not finer???
Even considering the loss of .7/.8g to the sink (due to 18g cannot fit into the 18g VST), that should not make the shot run 3X faster, and that the dark roast requires a grind 10 huge points finer than a medium roast.

Thanks guys for your input!
Notes: no channeling that i can tell, comes out evenly from naked portafilter, but it pours out so darn quick. No dead spots or spitters. No pin holes in spent puck that I can see. Jack leveler must be forced down to compact the dark roast (vs medium roast where leveler mass is enough to bottom out).

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#2: Post by yakster »

Sounds like the dark roast isn't as fresh. Did you get much crema?

LMWDP # 272

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#3: Post by Jeff »

"Too many variables, too little time"

I've found that darker roasts tend to require a bigger basket for the same headspace. I don't know that they're "fluffier", but I think there is some evidence that they are less dense than the same bean roasted medium-light or light. Said another way, 18 g of dark-roast takes up more space than 18 g of light-roast.

Now for the rest.

You ended up with a lower dose, so I'm not surprised it needed a finer grind to provide comparable "resistance" during extraction.

Darker roasted beans tend to be easier to extract. When you extract, you lose about 1/5 of the mass of coffee into the cup. If that goes faster because of the easier solubility, that's another factor.

Your local roaster is perhaps using better-quality beans. Starbucks is perhaps using commodity-grade beans.

Starbucks beans were probably roasted sometime this winter, or last fall. Your local roaster was probably within a week or two.


#4: Post by chipman »

That is exactly what Josuma advises when brewing their Malabar gold.

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#5: Post by Nunas »

Alex, I've a couple of comments that may help a bit.

As beans roast, they expand and get lighter. While the expansion is not a linear function of time, more or less, the longer they're roasted the greater they expand in volume and lose weight. This is why you're overflowing your basket with really dark (and probably stale) *$'s beans, but not with your lighter roast beans. You may want to consider getting a dosing funnel. A dosing funnel is a squat funnel that fits atop your portafilter and catches the grinds. Because the dark roast beans are so fluffy, if you give your portafilter a couple of smacks on your tamping mat/stand, they'll compact down quickly, at which point, you can remove the funnel. From there, they'll compact further with tamping.

As for changing beans and finding the right setting on your grinder, it isn't as simple as finding a setting for each one and then setting it there. The process, called dialing in, has to be done for each bean independently. Moreover, as your beans age, you have to make fine adjustments to the grind every day or two, usually finer, to pull in a given amount of time. This process has nothing whatsoever to do with the numbers/letters on your grinder's dial. In other words, you might buy a given bean this week and succeed in getting it dialed in. Then, buy the same bean from the same roaster in a week or two and find that setting the grinder to the same points does not work. I know this sounds like mission impossible if you're not used to dialing in, but, trust me, it gets to be fairly intuitive, once you're used to it for a while.

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#6: Post by HB »

alexanders5700 wrote:I mean dark beans should require coarser grinds, not finer?
That's not been my experience. Dark roasted coffees typically require a finer grind. Of course, there's always exceptions. For example, single origin coffees like an Ethiopian will require a finer grind than a "crowd pleaser" espresso blend, despite the latter being darker roasted.

Here's a key observation:
alexanders5700 wrote:I got the Starbucks Verona (Dark roast) (best before indicates 5 months in the future).
Stale coffee always requires a much finer grind than freshly roasted coffee. A "best before" date 5 months in the future is a statement for the stocker, not a statement about the window of opportunity for the best coffee experience. That said, there's quite a few threads on dark roasted coffees reporting they are good months post-roast; I don't recall ones making the same claim for light-to-medium roast coffees.
Dan Kehn

alexanders5700 (original poster)

#7: Post by alexanders5700 (original poster) »

Crema comparable to that experienced with the medium roasts (even at the accelerated speed).

I did check all the SB bags at the grocery store, all varieties, and out of all the bags (approx a dozen of each of the 4 SB varieties), the bag I purchased had the furthest best-buy date.

Does that mean it's still stale? Maybe, but it would have been the least stale (given all other best-buy dates were closer to the present).

alexanders5700 (original poster)

#8: Post by alexanders5700 (original poster) »

Yes that's it, a weight of 18g of the lighter (medium) roasts I've been using previously, gave a smaller volume compared to the larger volume that 18g of the darker (SB) roast.
I was already looking into a 20g VST basket to supplement my 18g, thank you.

alexanders5700 (original poster)

#9: Post by alexanders5700 (original poster) »

Decent funnel already on its way here. Should be getting it early next week.

I will be using that to grind directly into the portafilter, and it should help with the extra volume.

Although a newbie at physically performing the extraction, I have been researching for months (youtube, these forums, guides, tutorials etc).
I've seen that every new bean require dialing in, and as beans age, they require small adjustments.

My observation was more that let's say a guy like Hoffman has plenty of videos where when he moves from a darker roast to a lighter one, he reduced the grind size (to extract more from the harder-to-extract lighter bean). So that conversely means a darker roast is ground coarser.
But in this specific case of mine, the opposite, by a huge margin, was true... And I found that super weird/abnormal.

Also, the jump from a 17/18 to an 8 setting, that's a huge jump. I've seen Hoffman move his NZ one point, and get a 3-4 second change in shot time.
I had to move mine 10 points to get any type of shot time difference.
(Just to say, on the medium roasts, I did use grind size to dial them in. A 1 point move, or 1/2 point move on the NZ, would make a 3-4 second change in the shot time. For this dark roast, i moved it 8 whole points and no change in shot time).

The lost .7g in the sink would certainly make the shot faster, but I also know the VST baskets are +/- 1 g, so there are people pulling 17g shots out of the 18g basket (besides me)!

I'll try again tomorrow morning and see if grinding to even 5/6 setting will be enough to get the shot time to ~28 seconds

alexanders5700 (original poster)

#10: Post by alexanders5700 (original poster) »

I'll certainly be trying a local roaster with a dark roast, just the cafe didn't have any when i went, so I had to hit up the grocery store!

For the grind size, pretty much everything I read online shows finer grind size for lighter roasts (to get the harder-to-extract flavours).

If I google "grind size for espresso dark roast", the first two results are;
https://perfectdailygrind.com/2019/10/h ... ast-level/
https://baratza.com/dark-roast-versus-l ... r-grinder/

(as an example)

and both say grind finer for lighter roasts (ie, more coarse for darker roasts)