How do you improve extractions that start well but end badly?

[DC]

I have recently been trying to make some good ristretto shots (as measured by brew ratio) but have noticed that my extractions, despite starting evenly and progressing well for most of the duration of the shot, tend to fall apart after about 26 seconds. By this I mean dead spots appear around the cone, and the pour quickly develops the barber pole effect before running thin and watery.

I've tried up-dosing from around 14.5g to 16g and grinding finer, but this doesn't seem to be having much impact. I can't up-dose much further without encountering problems due to over-dosing the basket (Rancilio double). Would a different basket that provided more head space combined with a much higher dose of coffee solve this problem? Or is this another technique problem?

Thanks,
Dave
(Silvia/Rocky)

[Beezer]

Are you using the Weiss Distribution Technique? This seems to be very helpful in curing channeling problems, which is what you seem to be describing. Try dosing into a yogurt cup and stirring the grounds with a stick or needle to break up any clumps before tamping.

Also, make sure you level the grounds very carefully before tamping, and try a NSEW light tamp before doing your 30 lb tamp. You want to avoid any weak points in the puck that could allow water to channel through the coffee.

As for dosage, I think the correct amount should be enough to leave a faint screw impression on the puck after pulling your shot, but the puck should not touch the dispersion screen before the shot is pulled. In other words, leave some room for the puck to expand when the hot water hits it. One test is to see if the puck touches the screen by putting a nickel on top of the puck, then locking it in and taking it out again. If the coin gets pushed into the coffee, there's not enough space. Or something like that.

[DC]

Hi, thanks for the reply

Sorry, I should have mentioned.... I do use the WDT. Leveling is a bit tougher because I'm 'dosing under the rim,' and I do a nutating tamp followed by a hard straight-down tamp. As I understand it these sorts of things affect how well the extraction begins and progresses more than how it ends, hence me being a bit stuck for what to try next

[CGP4]

...tend to fall apart after about 26 seconds.

How much more do you want? I'd stop the shot at 25 seconds and enjoy!

[DC]

For 2oz shots I normally do stop around then but I want them to run longer for the ristretto (in the region of 30 to 35 seconds using Al's Rule) - stopping them where I am now they taste under-extracted.

[Dogshot]

I'm not sure why a finer grind is not solving this problem. Your coffee is less than 2-weeks old? Fresh coffee and a finer grind takes care of this for me every time. The only other thing I can think of is if your brew pressure is very high, this might cause your problem?

Mark

[CGP4]

I don't think I buy into Al's rule. But I do have a Silvia. You say the shot tastes "under-extracted" at the 25-second mark. I find, with my Silvia at least, that off-tastes are usually the result of poor temperature more often than not (assuming the grind and dose is in the ballpark). What is your temperature management routine? Are you waiting a certain amount of time after the boiler light turns on or off, etc.? I've found my shots improved tremendously once I took the time to figure out how to get my machine to deliver water as close to 200 degrees as possible. Unfortunately, it varies from unit-to-unit, so it takes experimentation. But I'd encourage you to explore that area. And, with a simple machine like the Silvia, the longer the pump is running the more likely your temperature is to fluctuate.

[DC]

I'm not sure why a finer grind is not solving this problem. Your coffee is less than 2-weeks old? Fresh coffee and a finer grind takes care of this for me every time. The only other thing I can think of is if your brew pressure is very high, this might cause your problem?

I was a bit surprised too. Maybe when I tried it something else went wrong to mask its effects... I had just started a fresh bag (2 days post roast). Pressure has been mentioned before, it and the OPV are on my 'to-check' list.

I don't think I buy into Al's rule

Why not?

What is your temperature management routine?

Dan's reverse surf technique. I don't know what temp this gives me on my particular Silvia, but it will be consistent. Ordinarily my shots don't taste like they have a brew temp problem. This is also on the 'to-check' list

[harris]

"dead spots appear around the cone"


I have noticed the same thing on occasion.
I am off to try the search button but if someone wants to help explain this, please.

[cannonfodder]

Are you using a convex tamper?

The center of your puck may be denser, try a cupped leveling where the coffee in the center of the basket is concave to match the curve in the convex tamper. Skip any nutating or tapping of the PF on a table to settle the grounds. I had a similar issue when dialing in my Elektra, I went to a lower dose, finer grind, no fancy taping or nutating (just a straight down tamp) and the problem went away. Thanks for the tip Jim.

[CGP4]

As I read it, Al's rule seems to state that a longer pull needs to spend less time with the grounds, so it doesn't over-extract, while a shorter volume needs a longer time to allow for sufficient extraction. But I believe the grind takes care of this without having to change the time. If you're pulling a lungo, the grind is coarser so it's already less likely to overextract; while a ristretto is already finer so more time will potentially overextract it.

Mark Prince (full thread here) states it better than I can:

Which can make sense to a certain degree, but I do not completely agree with the above any longer. Why? because it discounts something - the extractability of a given fineness of grind. In other words, I believe grind fineness plays a role beyond stalling or speeding up water flow - it also plays a major role in how much more or less can be extracted from a given gram of ground coffee.

But what do I know? How it tastes is what's important, so whatever path leads you to consistently good-tasting espresso is the right one for you to follow!