# Struggling with consistency



## Padowan (Aug 17, 2020)

I've been struggling to pull consistent shots for some time with my setup. I think it's a machine problem/feature as I have done everything I can think of to remove variability.

Setup: Nuova Simonelli Oscar II fitted with OPV set at 9.5bar, Rancillio Rocky Grinder, using a calibrated tamper and weighing my doses and yields on a digital scale, always purge the HX before each pour. Clean/backflush machine regularly.

Standard dose of 18g in a double basket. Tamp should be consistent with the calibrated tamper and I adjust grind/dose slightly with each coffee batch to aim for a 25-30 sec pour to a 50g yield.

I've tried to remove all the variables I can, but I still find that with the same batch of coffee my shots can vary wildly. One shot will be perfect, great crema, 25-30s pour time for around 50g yield. Next shot, identical conditions and it can be wildly different. Every so often I get multiple good shots in a row, without seeming to do anything different. I started keeping a norebook with all the conditions, grind size, dose, yield and pour time to keep track in the hope of honing in on consistent pours, but after logging several hundred shots in that book across multiple different batches of coffee I've stopped bothering.

The only thing left I can think of is to get a bottomless portafilter to see how the shots are developing and see if that gives an indication of channeling of inconsistent flow throught he puck.

Would really like to appeal to the experts on here to suggest what else I can try to increase my consistency.

Many thanks!


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## The Systemic Kid (Nov 23, 2012)

Important thing is to adjust one variable at a time so you know where you are. 18grms > 50grms is nigh on 1:3 so you are pumping a lot of water through the puck to get that. Try adjusting your ratio to 1:2 and tightening the grind to stay within 25-30sec extraction and see if that makes any difference.


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## John Yossarian (Feb 2, 2016)

In the end it might turn out that the Rocky is not up to the task, but as Systemic Kid suggested 50 g a shot is on the long-ish side.


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## Padowan (Aug 17, 2020)

I was using calibrated shot glasses to gauge yield before I had the digital scales so was aiming for a 60ml/2oz double shot as per the calibration markings. Considering (I expect) that the density of well pulled expresso is >1 that for an 18g dose, with a 2:1 yield of 36g, I'd probably end up with something more like 35ml or less which is closer to the Single Espresso 30ml/1oz or Double Ristretto 44ml/1.5oz markings.

Also read an intersting article about focussing on measuring the dose, hitting a yield and aiming for a time, with time being the last element to try to achieve - if my yield target has been wrong, then if I'm aiming for a time for the wrong yield that's not on the right track. Also read some interesting things about when to start your timer, pump-on vs first-drip - when Ilisten to my machine, the pump starts for a few seconds, then the solenoid clicks open, then of course a few seconds later the liquor starts to flow. I'm going to start my timing from the first-drop to again try to standardise and eliminate any slowness in the pump building up pressure.

I'll start adjusting the grind down to aim for closer to a 2:1 yield (by weight) and start getting a sense of what that equates to in volume for a good extraction.


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## John Yossarian (Feb 2, 2016)

I also use shot glasses and I aim to get a double ristretto dose, i.e. 44 mls. More often than not I am around the 40 mls mark. Sometimes I can have a shot for 35 sec but more often I am 40-45 seconds. I like what I get and this made me think that the timing, as you point out, is secondary.


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## catpuccino (Jan 5, 2019)

Padowan said:


> Also read an intersting article about focussing on measuring the dose, hitting a yield and aiming for a time, with time being the last element to try to achieve - if my yield target has been wrong, then if I'm aiming for a time for the wrong yield that's not on the right track. Also read some interesting things about when to start your timer, pump-on vs first-drip - when Ilisten to my machine, the pump starts for a few seconds, then the solenoid clicks open, then of course a few seconds later the liquor starts to flow. I'm going to start my timing from the first-drop to again try to standardise and eliminate any slowness in the pump building up pressure.


 Yes, for the most part ignore time. As above you might want to aim for a typical 25-35s range to get yourself into a typical extraction time when debugging, but your target should be an output weight. Ignore what you've read/people say about volumetrics, what's a single or double shot etc. Time from when you start the shot i.e. when the pump starts, 'slowness in the pump building up pressure' is irrelevant, any contact time between water and the grounds should be timed. Consistency is more important, but since we're in the business of eliminating variables, the orthodox approach is the time from the pump start.

Definitely get a bottomless portafilter. For ~£15 it's the single best value purchase you can make to learn about your extractions.

Are you single dosing the Rocky?



John Yossarian said:


> I also use shot glasses and I aim to get a double ristretto dose, i.e. 44 mls. More often than not I am around the 40 mls mark. Sometimes I can have a shot for 35 sec but more often I am 40-45 seconds. I like what I get and this made me think that the timing, as you point out, is secondary.


 Time is even less relevant for machines like the Vesuvius, my long pre-infusion low-pressure shots will often exceed 50s.


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## Rob1 (Apr 9, 2015)

Padowan said:


> I've been struggling to pull consistent shots for some time with my setup. I think it's a machine problem/feature as I have done everything I can think of to remove variability.
> 
> Setup: Nuova Simonelli Oscar II fitted with OPV set at 9.5bar, Rancillio Rocky Grinder, using a calibrated tamper and weighing my doses and yields on a digital scale, always purge the HX before each pour. Clean/backflush machine regularly.
> 
> ...


 Altering your ratio will not help you in any way, not sure why it has been suggested. If you like the ratio you're getting but want to get it consistently (which seems to be your point) then you need to look at other things. There's no "wrong ratio".

It isn't really clear what you mean though. You say



> One shot will be perfect, great crema, 25-30s pour time for around 50g yield. Next shot, identical conditions and it can be wildly different.


 Both have a 24-30 second pour for a 50g yield from the same dose but taste wildly different?


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## catpuccino (Jan 5, 2019)

Rob1 said:


> Altering your ratio will not help you in any way, not sure why it has been suggested. If you like the ratio you're getting but want to get it consistently (which seems to be your point) then you need to look at other things. There's no "wrong ratio".


 The long ratio is relevant because pushing that much water through the puck in such a short time is a big ask for a sub-part grinder and demands more of the puck prep, too. It could well explain much of the inconsistency, so since we're looking to debug and remove variables it's a fair start to aim for a more typical extraction time/ratio to see if shots remain consistent. It also raises the question of why OP is pulling a near 1:3 ratio to get the taste they want, which is far from common (though not wrong of course!).


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## MWJB (Feb 28, 2012)

catpuccino said:


> The long ratio is relevant because pushing that much water through the puck in such a short time is a big ask for a sub-part grinder and demands more of the puck prep, too. It could well explain much of the inconsistency, so since we're looking to debug and remove variables it's a fair start to aim for a more typical extraction time/ratio to see if shots remain consistent. It also raises the question of why OP is pulling a near 1:3 ratio to get the taste they want, which is far from common (though not wrong of course!).


 Not really, a 1:3 shot will likely be similar grind or a tad coarser as 1:2. If the grinder doesn't work (very unlikely & then it won't work at any ratio), or has a limit on how fine it will go, then a 1:2 shot will end up worse.

A long shot might be 1:5 or 1:6, these can be delicious, but obviously much weaker & very ugly pours.

If you're pushing the grind/grinder to its limits at 1:2, going longer on ratio will make shots more consistent, but maybe mouthfeel is a priority above consistency for some.


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## catpuccino (Jan 5, 2019)

MWJB said:


> Not really, a 1:3 shot will likely be similar grind or a tad coarser as 1:2. If the grinder doesn't work (very unlikely & then it won't work at any ratio), or has a limit on how fine it will go, then a 1:2 shot will end up worse.


 We might be edging away from OP's problem but when posting I was thinking back to my learner GC + Mignon days, where I was single dosing the grinder and using quite lights roasts and getting wildly inconsistent shots as a result. I pulled longer because it made for more consistent taste as you say, but at a certain point the puck had really gone to shit and by the end of the shot wasn't offering much resistance.

At any rate, reading back the post, as @Rob1 says it's not particularly clear what is inconsistent.


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## Rob1 (Apr 9, 2015)

catpuccino said:


> The long ratio is relevant because pushing that much water through the puck in such a short time is a big ask for a sub-part grinder and demands more of the puck prep, too. It could well explain much of the inconsistency, so since we're looking to debug and remove variables it's a fair start to aim for a more typical extraction time/ratio to see if shots remain consistent. It also raises the question of why OP is pulling a near 1:3 ratio to get the taste they want, which is far from common (though not wrong of course!).


 Sub-par grinders do better at longer ratios than shorter ones. The puck should be fine with 50g in 25-30 seconds. Maybe if it were a longer extraction time it would be an issue as you're still using a fine grind but putting it under pressure for longer.


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## catpuccino (Jan 5, 2019)

Padowan said:


> always purge the HX before each pour.


 Just noticed this. How long is it between each shot? Are you sure the purge is neccesary? Different HX machines behave differently, but my old ECM Mechanika needed a short cooling flush from idle but would be stable between shots as long as it didn't sit for 10+ minutes (in which case another flush, but shorter than the initial one..).


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## Philip HN (Nov 7, 2019)

I may be barking up the wrong tree, but I can't help but wonder whether the problem is actually much simpler (albeit I get the ratio question and did wonder myself). The OP sounds like he has immersed himself in the numbers but I wonder whether something fairly basic like a dosing cup might help deliver a good result in a way that more forensic analysis of the numbers might not. I used a Rancillio Rocky for years and although the size of the steps are a challenge, my sense is that the degree of inconsistency described is more likely to be due to puck preparation issues. And of course I'm a recent convert to dosing cups, so what else can I say...


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## Padowan (Aug 17, 2020)

Thanks for all the replies so far, lots of interesting points.

A good point was raised about whether my target (or how I have been targetting) is 'right' or not. A question I have on that is does that matter with regard to consistency? I seem to be unable to make either consistent 'good', or consistent 'bad' shots. Keeping all the parameters that I can measure the same, I get different results (in terms of output rather than quality/taste). In general the flow out of the portafilter tends to start slow, you hear a change in pitch of the pump as pressure starts to build and then I get not so much a torrent, but a much increased flow, I don't have a steady gentle flow rate out of the portafilter throughout the pour.

To add some more details on the unquantifiable parameters here's my puck preparation technique: I grind (and weigh) the coffee into a small dosing cup (my Rocky is a non-dosing version). I then stir up the coffee with a little wooden skewer to break up any lumps. I then deposit this through a little make-shift funnel into the portafilter. Next, I then knock the portafilter gently against my hand a couple of times to level off the bed and then I remove the little funnel. I then place my calibrated tamper on top of the bed and ensure that it is level before pressing it down until the spring just starts to give. So although I can't measure most of those steps, I am doing the same thing as much as I am able to do...

I've certainly taken away that I should reduce my yield expectation (from around 3:1 to around 2:1) to be targetting something that is more clasically understood to be correct. My first step in that direction will be to reduce the grind as I feel that if I'm achieving a longer output that I should be targetting, I am probably "blowing through" the puck too fast, which won't be good for quality, so a finer grind will help in that area, but also blowing through is likely to add a very large variability if the puck is disturbed more or less by the igher-than-desired flow rate and could lead to some of the inconsistency I am seeing....

This morning I tried 2 shots and the taste was certainly better (sweeter, less sour) with a lower yield (38-40g for a 18.5g dose) and the flowrate was visually more stable through the pour. Will try another couple with the same parameters this morning and see how they go.


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## Rob1 (Apr 9, 2015)

Padowan said:


> Thanks for all the replies so far, lots of interesting points.
> 
> A good point was raised about whether my target (or how I have been targetting) is 'right' or not. A question I have on that is does that matter with regard to consistency? I seem to be unable to make either consistent 'good', or consistent 'bad' shots. Keeping all the parameters that I can measure the same, I get different results (in terms of output rather than quality/taste). In general the flow out of the portafilter tends to start slow, you hear a change in pitch of the pump as pressure starts to build and then I get not so much a torrent, but a much increased flow, I don't have a steady gentle flow rate out of the portafilter throughout the pour.
> 
> ...


 I'm massively confused...keeping all parameters the same you get different output? So you're not keeping all parameters the same then? You get a different output but the quality/taste is the same???

I think you need to define these "parameters". To most people parameters of espresso or coffee are numbers used to measure everything. Basically, dose, weight out, time. If the weight out or time is changing then parameters are not the same.

If you're not actually changing the parameters and are just talking about inconsistency in terms of flow rate then the flow rate you're seeing is just visual. Over the shot the flow rate is the same if you hit the same yield in the same time. You're probably seeing channeling here. You may also be seeing fines migration, especially if you are single dosing the grinder. Running with a few doses in a hopper will probably give better results. If you do run with a few doses in the hopper but let it run to empty that's another potential cause of inconsistency.

So in order:

No ratio has nothing to do with consistency.

Grinding finer to achieve your new lower ratio makes it harder for you to achieve a higher/normal EY compared to a longer yield at the same grind setting. You may be extracting below the point where you would get sourness now rather than above it. A high flow rate through a coarse grind will mean you get a lower max pressure and a longer yield, this can be a more balanced extraction, getting closer to a filter brew at very long yields. I'm not sure what the stuff about blowing through the puck is about. It's possible you've been grinding too fine and the puck has been falling apart under pressure in your previous shots (if flow rate rapidly increases), if you've been single dosing the grinder that might be another reason to see that (inconsistent grind rather than too fine).


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## Padowan (Aug 17, 2020)

Rob1 said:


> I'm massively confused...keeping all parameters the same you get different output? So you're not keeping all parameters the same then? You get a different output but the quality/taste is the same???
> 
> I think you need to define these "parameters". To most people parameters of espresso or coffee are numbers used to measure everything. Basically, dose, weight out, time. If the weight out or time is changing then parameters are not the same.
> 
> ...


 Let me try to explain when I mean by consistency then, as my noobiness is obviously causing confision in my terminology.

When I refer to parameters I am referring to static input parameters that are things that I can control ahead of pulling the shot, so this would be a particular grind setting, dose weighed on a digital scale into a dosing cup (no doser on the grinder), puck preparation/tamp (calibrated tamp) and any machine setting you can set (in my case as I have an OPV I can fix that). You then have output 'parameters' which can be measured but they are a function of the 'performance' of the pour - so this would be volume/yield and time (there's also perhaps a less measurable one around how the flow appears to change through the pour, or not). Finally there are the more subjective measures of the quality of the shot in terms of taste etc which are not so easy to quantify, but are still something that you want to achieve.

My issue is that when when I fix all my static input parameters I do not have consistent output results. If I stop the pour at a 40g yield (measured on the digital scales), one shot might get that in 15 seconds, another time it might take 30 seconds with identical input parameters. Alternatively if I always take a 25 second pour, one time I'll get 40g another time I might get 80g (which is the situation I refer to by 'blowing through the puck' - assumed to be some kind of channeling). I can immediately tell whether the pour will be long or short by the appearance of the flow out of the portafilter, but as I don't have any way to measure that it's just an indicator. Every so often I pull a great shot, good yield, good body, great crema, nice taste and I think I've got everything dialed. Then I pull another one in exactly the same way (same preparation and same pour time) and it's different, and by that I mean that I will have pulled the previous shot using the 25 second button and the next shot I pull using that same time might end up coming out at 80g and will consequently be watery and likely sour.


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## MWJB (Feb 28, 2012)

Padowan said:


> Let me try to explain when I mean by consistency then, as my noobiness is obviously causing confision in my terminology.
> 
> When I refer to parameters I am referring to static input parameters that are things that I can control ahead of pulling the shot, so this would be a particular grind setting, dose weighed on a digital scale into a dosing cup (no doser on the grinder), puck preparation/tamp (calibrated tamp) and any machine setting you can set (in my case as I have an OPV I can fix that). You then have output 'parameters' which can be measured but they are a function of the 'performance' of the pour - so this would be volume/yield and time (there's also perhaps a less measurable one around how the flow appears to change through the pour, or not). Finally there are the more subjective measures of the quality of the shot in terms of taste etc which are not so easy to quantify, but are still something that you want to achieve.
> 
> My issue is that when when I fix all my static input parameters I do not have consistent output results. If I stop the pour at a 40g yield (measured on the digital scales), one shot might get that in 15 seconds, another time it might take 30 seconds with identical input parameters. Alternatively if I always take a 25 second pour, one time I'll get 40g another time I might get 80g (which is the situation I refer to by 'blowing through the puck' - assumed to be some kind of channeling). I can immediately tell whether the pour will be long or short by the appearance of the flow out of the portafilter, but as I don't have any way to measure that it's just an indicator. Every so often I pull a great shot, good yield, good body, great crema, nice taste and I think I've got everything dialed. Then I pull another one in exactly the same way (same preparation and same pour time) and it's different, and by that I mean that I will have pulled the previous shot using the 25 second button and the next shot I pull using that same time might end up coming out at 80g and will consequently be watery and likely sour.


 If with the same grind, coffee & dose you get 40g out in either 15s or 30s, something is very amiss with your prep. Otherwise this doesn't happen.

The output parameter you should focus on is the weight out, the time might vary by a few seconds to get 40g, but this is normal & can shift again with different coffee.

Subjective taste can be broken down simply into: like a lot, like a little, neither like/dislike, dislike a little, dislike a lot.

What is a "25g button"? Try starting & stopping the pump manually, allowing for a little 'run on' to hit your 40g target. It sounds like your inconsistency is coming from reliance on a wonky volumetric/timed pour system.


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## Blue_Cafe (Jun 22, 2020)

Padowan said:


> Let me try to explain when I mean by consistency then, as my noobiness is obviously causing confision in my terminology.
> 
> When I refer to parameters I am referring to static input parameters that are things that I can control ahead of pulling the shot, so this would be a particular grind setting, dose weighed on a digital scale into a dosing cup (no doser on the grinder), puck preparation/tamp (calibrated tamp) and any machine setting you can set (in my case as I have an OPV I can fix that). You then have output 'parameters' which can be measured but they are a function of the 'performance' of the pour - so this would be volume/yield and time (there's also perhaps a less measurable one around how the flow appears to change through the pour, or not). Finally there are the more subjective measures of the quality of the shot in terms of taste etc which are not so easy to quantify, but are still something that you want to achieve.
> 
> My issue is that when when I fix all my static input parameters I do not have consistent output results. If I stop the pour at a 40g yield (measured on the digital scales), one shot might get that in 15 seconds, another time it might take 30 seconds with identical input parameters. Alternatively if I always take a 25 second pour, one time I'll get 40g another time I might get 80g (which is the situation I refer to by 'blowing through the puck' - assumed to be some kind of channeling). I can immediately tell whether the pour will be long or short by the appearance of the flow out of the portafilter, but as I don't have any way to measure that it's just an indicator. Every so often I pull a great shot, good yield, good body, great crema, nice taste and I think I've got everything dialed. Then I pull another one in exactly the same way (same preparation and same pour time) and it's different, and by that I mean that I will have pulled the previous shot using the 25 second button and the next shot I pull using that same time might end up coming out at 80g and will consequently be watery and likely sour.


 If you are getting variables of 100%> on shots, then i think you have either something changing with your setup or the machine, or you. There are variables, but not that much unless something is wrong.

As a observation.

Springs are a variable load device. They will impart different reactions depending on the force exerted. For your tamper, as i atm understand it, once the puck is compressed, that's it. You could sit an elephant on it and the puck won't change much. So, i don't like how you use the calibrated tamper. Just push it all the way down till it hits the stops. THAT will be the most consistent way.

And what did you do to the OPV? Is this done well and working correctly?


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## Rob1 (Apr 9, 2015)

Ok so now it's clear what you're doing.

Are you single dosing the grinder every time or dropping a few doses in at once occasionally? I'd say stop single dosing the grinder anyway as this will help consistency. Make sure you're purging stale grinds.


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## Padowan (Aug 17, 2020)

MWJB said:


> If with the same grind, coffee & dose you get 40g out in either 15s or 30s, something is very amiss with your prep. Otherwise this doesn't happen.
> 
> The output parameter you should focus on is the weight out, the time might vary by a few seconds to get 40g, but this is normal & can shift again with different coffee.
> 
> ...


 I agree something must be amiss, but I can't for the life of me work out what it is. I'm an engineer, I know how to do things methodically and am trying to be as systematic as I can to bottom out this problem, but something either in my prep, or with the machine is giving much greater variability than I would expect.

The "25 second button" is indeed a timed pump run time. I can set the duration on 2 buttons to whatever I want so that I have a one press "standard" time for a pour. Of course I can start and stop the pour whenever I want too, was trying to fix one other parameter by having a standard duration.



Blue_Cafe said:


> If you are getting variables of 100%> on shots, then i think you have either something changing with your setup or the machine, or you. There are variables, but not that much unless something is wrong.
> 
> As a observation.
> 
> ...


 Calibrated is perhaps the wrong word. The handle has a spring in when you achieve a given force the spring starts to compress and the handle moves. There's about 5mm of travel before you bottom out the travel. At that point I stop. According to my bathroom scales that's happening at around 30lb of force.



Rob1 said:


> Ok so now it's clear what you're doing.
> 
> Are you single dosing the grinder every time or dropping a few doses in at once occasionally? I'd say stop single dosing the grinder anyway as this will help consistency. Make sure you're purging stale grinds.


 No doser on the grinder. I grind straight from the bean hopper (into which I tend to put a 250g bag of beans at a time into) into my dosing cup the amount I want in the portafilter. Its not a zero retention grinder, so I will always run several shots worth out when I change the grind setting.


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## MWJB (Feb 28, 2012)

Padowan said:


> The "25 second button" is indeed a timed pump run time. I can set the duration on 2 buttons to whatever I want so that I have a one press "standard" time for a pour. Of course I can start and stop the pour whenever I want too, was trying to fix one other parameter by having a standard duration.


 This is what's largely causing the inconsistency. Coffee takes time to brew, but time by itself does not drive extraction. At a constant grind setting & ratio, weight out does.

A standard duration is not something you really want.


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