Flow rate differences across roast levels?

Ernie1

I mentioned in the C40 thread I’d been trying some lighter roasts (having mainly preferred darker) which I’ve been really enjoying.

One thing I’ve noticed is that the flow rate is wildly different on lighter roasts. On med-dark roasts I get a pretty consistent flow across the extraction, ramping up slowly start to finish.

On light roasts I’m getting nothing for the first few seconds, a few drips and then a pretty steep ramp up to finish. Almost like the puck fractured but it hasn’t, and it seems to happen regardless of prep.

The cup tastes great, and I know that’s really the only thing that matters but I’m curious to know if anyone else experiences this and what it is that causes flow to behave differently on lighter roasts.

MediumRoastSteam

Ernie1 - I have to say it’s the same story for me. Light roasts behave somewhat very different from darker roasts, and I’m sure that’s to do with origin too as Dave says.

I suppose one of the advantages of a Flow Control Valve so you could decrease it as the shot progresses, specially for light roasts.

CoyoteOldMan

Ernie1 FWIW, I have the same experience on the Leva. Not that the coffee comes out bad, but the flow and timing seem to be very different depending on roast level.

Then again, @LMSC and @Cuprajake seem to have figured out how to regulate flow a lot better across a wide set of coffee varieties and roasts… so in my case it may be more operator and coffee than just the coffee itself.

DavecUK

They can be a bit more challenging, especially certain Origins (which are more difficult roasted light or darker) which favour light roasting.

I assume it’s for a couple of reasons.

Inconsistent roasting as some very light roasts are not well developed
less porosity, which additionally links to the point above.

I tried roasting much lighter for a while, but neither I, nor my roast sharers liked it.

LMSC

I have no idea what the flow rates of my shots are. I still use my hand grinder for light to medium. My preference is also light to medium, with the decaf being an exception.

For me, the lighter the roasts, the tighter the grind, which can be 4-6 micro clicks on my hand grinder.
Certain coffee are less soluble — for example Costa Rica, Honduras. IMO, it can channel or pour faster. Normally, one may need to increase the dosage to address the strength and the pour. This can be a problem with certain baskets. I rather prefer grinding a bit finer for espresso. If I am brewing, I straightaway up dose it, say from a typical 65g/l to 70-75g/l.
Certain coffee aren’t - example, certain Kenyans and Ethiopians. They can also be fluffier. I would normally dose 16.3g-16.5, grind a bit coarser and tamp normal.
I had one coffee bag, where I struggled to decrease the shot time. The water was struggling to go thru the puck. It was the Blackcat’s Indian Araku. Rather than reducing the dosage, I dosed the same weight and the grind size and loosely tamped. This helped.
On the opposite side of the spectrum was the Smith Street Columbian Anerobic. It was too fast as the shot lasted under 20s for 41g.. Our MediumRoastSteam advised me to grind tighter and up the temp to address the pour rate and the acidity. This was great and I ended up getting a steady good pour for the same ratio lasting about 35s. I had to grind 5-6 micro clicks tighter for the shot.
Finally, a good puck prep / distribution is important. Get a WDT tool or see how you can improve the distribution. I find the WDT boring, but don’t see a way out. 😊

Edit :

I won’t worry about the spent puck showing a ring or a crack, as long as it doesn’t affect the pour and the taste, provided there are no silts into the cup. I think cracks may be the sign of a fine grind. But, addressing this may create other issues.

Ernie1

Interesting, thanks for the replies.

I find when dialled in well there’s some great flavours to be had from the lighter roasts I’ve tried but it has proven tricky to get it right. With some of the lighter SO’s costing upwards of £12 for 250g, I can see it becoming very expensive.

Sadly no longer having the Bianca means my flow control valve now goes all the way from 0-9 bars… just with nothing in between 😅

Cuprajake

smoke and mirrors i have a sophisticated editing computer that allows me to make my videos appear that way, yet looking like they have been filmed on a potato

joking aside, i use wdt, and light tamping pressure, i wouldnt call my basket prep the best, saving grace is the leva is forgiving as hell.

for flow basket, grind and dose are important, its amazing how many shots crack

Ernie1

I’ve just switched back to trusty Rave Chatswood from the New Ground and flow throughout the shot is night/day different yet still great in the cup and still a similar overall extraction time.

When I say flow rate I mean by eye, I’ve not actually measured it but it’s easily noticeable. If I buy another lighter roast I’ll video it.

MWJB

So what’s the difference in total shot time for good tasting light & dark shots at the same ratio?

Ernie1

MWJB

28 seconds-ish for both! That’s what is interesting. The 28 is arbitrary but the fact they’re the same overall time but flow totally differently.

MWJB

Darker roasts are known to shatter into more fines, maybe this has a bearing in the appearance of the latter part of the shot, with the lighter roast looking more ‘ragged’ - I find it best not to look :-) …along with the lighter roasts being a little denser?