Medium-light roast espresso too acidic - help

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#1: Post by Ricci »

Hi all
I'm reasonably new to the Barista game.
I'm struggling to find the cause of my sour/acidic espresso.
I'm using a freshly roasted bean, about 11 days old now.
Its pulped natural Brazilian coffee blended with a microlot Colombian coffee. The blend is from a reputable roaster.
I have a new LMLM and borrowing a Victoria Arduino Mythos 1 until my grinder arrives.
I've dialled in what I think is a very fine grind.
I dose into a cup and use a WDT tool as there are quite a few clumps straight out of the grinder. Once in the basket I do a light tap on the counter and then St Anthony's distribution wedge. I tamp fairly hard with the intent to increase extraction time.
21 grams in, 42 grams out, 30 second extraction time and the shot tastes very acidic.
Currently not using pre infusion as I'm not sure what I should be setting it to.
Coffee extraction seems to be quite thin coming out of the portafilter, but it seems like a nice gradual transition from dark to light.
Shots seems to be pretty consistent, however the puck is crumbly and difficult to bump out of the portafilter. No signs of channeling though.
I have read that water temp plays a big part and so I have increased the temp on the machine to 97degreesC. Has made a very slight difference but still very acidic.
I'm at a bit of a loss, any help would be great.
Not sure how much finer I can grind as it's already very fine.
Thanks in advance!

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MTN Gert

#2: Post by MTN Gert »

A few things to try.

The LMLM temp wheel is not very accurate and it might be a good idea to keep turning up the temp 1°c at a time until it tastes right or even slightly bitter

A longer extraction on a light roast may help in the 35 second range

Changing brew ratio can really help. Try a 1-2.5 all the way up to a 1-3 ratio

Sometimes I get my best results out of a 16-18g basket vs the 21g triple . Even with brew ratios being the same a different starting dose can make a big difference

Let me know if this helps. Good luck!
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#3: Post by Jeff »

For me, for medium-light and light coffees, 17 g is my standard dose. I tend to pull 1:2.5-1:3

You won't get those gloppy shots out of a lighter roast. It's a different drink, though prepared on the same equipment with similar ingredients.

Grind finer and use a longer preinfusion, if you have that option. Finer grind means more surface area per volume of grind, so easier to extract. The longer PI lets the puck "soften" so that you can get the higher flow rates that can help getting higher extraction (as opposed to just choking the machine).


#4: Post by mtbizzle » ... o-compass/ << That's a helpful tool.
As it suggests, I would try a longer shot. You could try upping temp as suggested too. Some of the decent espresso crowd like lighter roasted espresso a lot, and often pull shots with 1:3-6 ratios, though the longer end of that spectrum (1:5, 1:6) is not a standard type of shot ("rao allonge"). Do you by chance know the characteristics of the water you are using? I am told that espresso, for the sort of reason you are talking about (high acidity), can tolerate quite high alkalinity (things like sodium bicarbonate, potassium bicarbonate) to tame that aspect of the shot.

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#5: Post by spressomon »

I have had success reducing acidic brightness on medium-light roasts by lowering the brew temp and lowering the brew pressure.

And, longer slower pre-infusion will allow a finer grind which also can bring sweeter flavor to the cup.

Not unusual for me to pre-brew (Slayer term) 20-28 seconds then pull at 7.5 BAR...using lighter roasts.
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Ricci (original poster)

#6: Post by Ricci (original poster) »

Thanks for the replies.
Definitely a few different things to try out there. Will let you know how I go.


#7: Post by Tyme »

I have a similar problem with a much worse machine that yours, so this may not apply. But my grinder is super clumpy too and I use a distribution tool and WDT. I'm still in the process of fixing my acidity, but I think I got a definite improvement when I did WDT much more thoroughly than before. Before, I would just stir the grinds for a few seconds, mostly on the surface. Now, I stir for 20-30 seconds, making sure I reach all the bottom corners of the puck and the surface is super broken up, leaving absolutely no clumps visible or buried. If you have a really clumpy grinder and your WDT consists of only a couple quick stirs, maybe try this out.

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Ricci (original poster)

#8: Post by Ricci (original poster) »

I have been experimenting and tasting a lot of coffee over the last week or so. Haven't had the best of sleeps :shock: :)
So I have been getting far better results with a smaller dose, finer grind and longer ratio.
Yesterday I pulled a balanced shot, probably the best I've done on the machine so far. I feel like the machine is kind of wearing in a bit as well...Only the Vacuum Breaker is leaking now......
La Marzocco are sorting it out and sending a tech to fix it.
Overall I'm pretty happy with my progress. Turns out my grind fineness could go a fair bit finer as well.


#9: Post by HRC-E.B. »

In short, I'd say do all you can to promote more complete extractions.

Best distribution possible to ensure even extractions.

Slightly finer grind and lower dose to promote more even temperature penetration through the puck.

Slightly longer shot (1:2.5, 1:2.8 ratio).

Slightly longer extraction.

This all should help a bit.