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Trials and errors! OPV's and distribution tools!


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Ive had my GC for a couple of weeks now and I'd say in 2 bags of beans I've had 1 ok shot. I generally make it into a flat white so not all that coffee was wasted, however, I've always tasted everyshot before adding milk so I can get used to adjusting the sour / bitter taste profiles, mouth feel and the like. 

What a learning curve, generally most shots have had sourness except a few. For other newbies like me, if you struggle to differentiate, then from my basic knowledge so far sourness is fairly instant as you first taste the espresso, you feel it on your tounge.. like a slight fizziness, If your not sure what I mean eat some haribo tangtastics. Bitterness is felt by the back of your mouth and lingers in your throat as an unpleasant aftertaste. 

So back to sourness, this was accompanied by a quick pour so I would adjust the grind finer, the initial part of the pour being slower then it would always speed up, channeling was evident removing the puck, that's if it hadn't collapsed and exploded all over the shower screen..Ummmm..... 

Then a I realised, the Motta 58.5mm distributer/levelling tool I was using was adjustable. ( Not easily evident as no instructions.) so all I was doing was flatening the top of the puck before tamping, and tamping wasn't actually distributing properly... problem 1..

While I was thinking about this problem I realised when I first got the GC classic when it arrived the first thing I did was change the steam wand, then adjust the OPV to 10 bar. Since then I've de-scaled it (made a huge difference to taste, as the machine hadn't been used for a few years and I installed a Shades PID. It got me wondering after these changes whether I had a high pressure problem or whether it was just amateur puck prep (most likely). So I put my analytical hat on further and wondered what the OPV reading was now. (I was just reading on other threads the OPV adjustment should be done cold because most of the cheap pressure gauges are only rated to 60 deg C is my understanding, I'm maybe wrong in this assumption)..But your machine does not operate cold. So I warmed it up fully for 20 mins. (I've discovered by putting a milk thermometer through the holes across the porta filter spout (standard portafilter). It stabilises at 71 degrees. If you run water with it in place it rises to about 85..then drops back after 5 minutes to 71. That tells me temp in the machine has stabilised. 

So I ran the pressure gauge with a hot machine and hey presto it's showing 1 bar higher at 11 bar. So I adjusted it hot back to 10 bar (1/4 turn anti clockwise was perfect), and the results from the first shot were much better!. 

Only time will tell whether these 2 things will improve my consistency. And I may be way off the mark with both but wanted to share my experiences. 

Any experienced hands with far great knowledge than me, please feel free to correct me on any of the above.

 

 

 

 

 

 

 

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Hard to see where pressure is being affected by heat as the safety valve hack you have done is on the cold side of the boiler and any PVT changes due to heat should be automatically moderated by the valve setting?.

 

Pressure gauges work on the bourdon principal. It may be that if the gauge is not temperature compensated (unlikely) you are just reading additional "bourdon effect" from thermal expansion on the coil as an increased pressure reading.

Maybe.

 

 

 

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I'm almost at the same point as you in my 'coffee' journey using my (new to me) GC.  My pressure gauge arrived the other day from @FairRecycler (many thanks!) and I used it to set my OPV to around 9.5 bar.  I did find that my pressure via the blind basket was different to when making coffee and it never seemed to be the same thing twice.  When I got my GC, I had taken it all to pieces but maybe I hadn't cleaned the OPV fully the first time, so I removed it, stripped and descaled it in some citric acid solution, refitted it and re-set the pressure once more.  It now seems to be a lot more stable and I'm just awaiting delivery of my PID bits then I can fit that and remove another variable.  Then, as with you, it's all down to the coffee, preparation, tamping etc etc.  I'm sure we'll both get there with help from this forum!!

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One of your problems may be the distribution tool. They will not effectively level the grinds so they need to be fairly level before being used. If not the high parts get more compression than the low leading to unequal pressures in the grinds across the puck.

What they can do if the grinds are pretty level is help to keep the tamp square. Use lightly leaving some further compression for the tamper.

Some people fully tamp with them but then have no idea what the tamping pressure is - not a problem really as their depth can be adjusted. The dose needs to consistent though. A few 1/10g variation probably makes little difference. They can apply very high pressures though due to the slopes in their shape.

Seeing another post - It's normal to see higher pressures when a blind basket is used. The OPV opens more which means more compression of the spring in it.

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On 13/03/2021 at 22:06, FlyingPianist said:

Ive had my GC for a couple of weeks now and I'd say in 2 bags of beans I've had 1 ok shot. I generally make it into a flat white so not all that coffee was wasted, however, I've always tasted everyshot before adding milk so I can get used to adjusting the sour / bitter taste profiles, mouth feel and the like. 

What a learning curve, generally most shots have had sourness except a few. For other newbies like me, if you struggle to differentiate, then from my basic knowledge so far sourness is fairly instant as you first taste the espresso, you feel it on your tounge.. like a slight fizziness, If your not sure what I mean eat some haribo tangtastics. Bitterness is felt by the back of your mouth and lingers in your throat as an unpleasant aftertaste. 

So back to sourness, this was accompanied by a quick pour so I would adjust the grind finer, the initial part of the pour being slower then it would always speed up, channeling was evident removing the puck, that's if it hadn't collapsed and exploded all over the shower screen..Ummmm..... 

Then a I realised, the Motta 58.5mm distributer/levelling tool I was using was adjustable. ( Not easily evident as no instructions.) so all I was doing was flatening the top of the puck before tamping, and tamping wasn't actually distributing properly... problem 1..

While I was thinking about this problem I realised when I first got the GC classic when it arrived the first thing I did was change the steam wand, then adjust the OPV to 10 bar. Since then I've de-scaled it (made a huge difference to taste, as the machine hadn't been used for a few years and I installed a Shades PID. It got me wondering after these changes whether I had a high pressure problem or whether it was just amateur puck prep (most likely). So I put my analytical hat on further and wondered what the OPV reading was now. (I was just reading on other threads the OPV adjustment should be done cold because most of the cheap pressure gauges are only rated to 60 deg C is my understanding, I'm maybe wrong in this assumption)..But your machine does not operate cold. So I warmed it up fully for 20 mins. (I've discovered by putting a milk thermometer through the holes across the porta filter spout (standard portafilter). It stabilises at 71 degrees. If you run water with it in place it rises to about 85..then drops back after 5 minutes to 71. That tells me temp in the machine has stabilised. 

So I ran the pressure gauge with a hot machine and hey presto it's showing 1 bar higher at 11 bar. So I adjusted it hot back to 10 bar (1/4 turn anti clockwise was perfect), and the results from the first shot were much better!. 

Only time will tell whether these 2 things will improve my consistency. And I may be way off the mark with both but wanted to share my experiences. 

Any experienced hands with far great knowledge than me, please feel free to correct me on any of the above.

Hello - sourness can be attributed to many things. First an obvious question - what is the roast profile / tasting notes of the bean (if fruit forward, lighter roast, it will probably taste sour at a 2:1 ratio). You're mentioning evident signs of channeling in the puck - what are your cues to suggest this?

Dose: what size dose are you using? Assuming you are using the stock double so should be 14g(ish). As you're mentioning obliterated pucks, perhaps you are over/under dosing. I'm assuming you are weighing (if you care enough to ask, you should be weighing).

Grind Size: the coarser=faster / finer = slower relationship works up to a point but you can grind so fine that you cause channeling. You might want to take yourself 1.5 numbers coarser on the grind setting (Specialita if I remember correctly) to do a 'hard reset' on the grind size. Make big changes (whole numbers) to get obviously too coarse/fine and then step down to half numbers to get you ballpark right. Keep the puck prep consistent throughout as you don't want variability in prep to erroneously cause you to change grind.

Distribution / Tamping: as stated by @ajohn the leveler will not distribute for you and can lead to a false sense of visual security - if you switch to bottomless then you can see distribution quality play out during the shot. There are a load of techniques to try and get level (I grind into a dosing cup, WDT, tap down on the worktop, spin a leveler, then tamp). The downward tap is used by many to try and collapse air pockets before tamping.

OPV Setting: generally accepted practice is to extract at 9bar, but there is now a following for 6.5bar extractions. Once you sort distribution and grind, play around with pressure.

Good luck!

PMA all day!

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Thanks for the suggestions and info.. Thought I'd follow up with some more details. 

Sourness: This has improved massively in the last bag of beans (Argyll Coffe Roasters Brazilian). (A recommendation I would have in hindsight would be to start with a 1kg bag of beans to give time to learn the taste profile and the subtle changes the different recipes makes to taste, otherwise like me you just start to get somewhere and the beans run out and it's like starting over with new bag, which gets frustrating). This is also after adjusting the OPV and the depth of the distribution tool. I've had much more consistent results.

 

Channelling: after pulling a shot and removing the portafilter there are often 2-3 small (2-3mm diameter) sink hole shapes in the puck. As the shot pours, it often starts slow and the flow increase as pour time increases. Probably as much to say the last 15 grams pour 50% faster than the first. 

Weighing: For the latest beans I've been single dosing into a dosing cup. (Much less mess and easier to prep a 2nd shot ready). Weighing the beans before grinding and weighing the grinds afterwards. Always using 15g +-0.1g in the standard 14g basket. (I agree I need a bottomless filter, it's next on the shopping list when my budget gets replenished). 

Puck prep:

1) Using the porta filter upside down on the dosing cup and turning up. 

2) Distributing across the puck with a cocktail stick lightly to spread evenly and level out. 

3) Tap the portafilter a couple of time on the counter top

4) Using the Motta distribution tool to flatten. (Which seems effective to tamp also) 

5) Tamping after doesn't appear to move the grinds at all with sensible pressure. (So maybe I've got the Distribution tool set to deep). 

The puck is dead level after this. 

Pour is currently 28 secs,15g in 30g out. Taste is much better than before and fairly consistent. Still get the parent channelling holes though. So based what you said Kjk maybe to fine a grind? Might help a steadier pour? 

This was my best looking and best tasting shot to date. The latte art is a bit hit and miss! I'll try and get one of the puck when I next make one if that would help.

20210312_110802.thumb.jpg.9a01841634db08a50e8ef32b3156997c.jpg

 

 

 

20210313_115417.jpg

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It sounds like you’re getting there, if the coffee is tasting better than I wouldn’t question too much. Just checked their site - is it the tropical fermentation coffee - tasting notes are mango and lemon so unsurprising if you’re getting sour. If I’m correct on the bean you could try pulling longer (maybe 1:3 or 1:4) - sour/salt tastes extract first, then the sugars, followed by the bitters so you may have more time to play with the extraction, you can also coarsen up the grind against the ratio.

It’s normal for the shot to flow faster towards the end as extraction is physically removing material from the coffee causing the puck to degrade. You can’t do much about this unless you have flow/pressure profiling.

I sometimes get little pinholes in the top of the puck but haven’t correlated it to horrible coffee. If your coffee is tasting good then you can enjoy it and be proud of the progress you’ve been making.

PMA all day!

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Posted (edited)

Thanks Kjk, great to know about the flow. I've been getting so frustrated expecting the flow to be similar throughout the extraction. 

Yes thats the coffee, I had the Ethiopian before that, which also has citrus notes. Although in all the shots I've tasted I can taste distinct difference between those that have flowed to fast and been very sour (instant type tingling on the tougue) and a shallow taste and those that have been more rounded and  the citrus notes ending in the middle of the mouth. 

 There's just been 1 or 2 that just seem to flow like the honey description the have an almost creamy texture in the mouth that also really tastes good. They may have flowed a little faster towards the end but always held together without the little splashes I seem to get with others. 

 The sour/sugar/bitters description has really simplified my understanding. I've been looking at some of the taste profile charts and just find them confusing and in all honesty I had the opposite in my head, thinking the strongest bit came first which I associated with bitter so you've realigned my thought process. If I was to simplify that then and pull a 1:1 shot it should be sour, and and 1:3 shot become more bitter? 

Edited by FlyingPianist
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Just to add that the general statement only applies if there is uniform extraction (little to no channelling). If there is significant channelling some areas of the puck are over and others under which can lead to a simultaneous sour/bitter effect which is maddening to troubleshoot.

If you really want to geek out there are a couple of good posts from Barista Hustle: Extraction and the Espresso Compass. They are in the camp of fix dose (grams dry), target yield (wet grams out) and use time as an indicator.

You are balancing a lot of things in your recipe that could be reduced to taste, strength, and mouthfeel. Taste is getting into the literal sweet spot between sour and bitter (assuming good even extraction). Strength will start high and become more dilute as the rate of extraction decreases - the first drips of a shot will be more “pure coffee taste” than the last. Mouthfeel is linked to strength as it comes from the non dissolved particles in your shot which become more dilute as you push more water through.

It’s up to your preferences to decide what you want to target (I prioritise taste) but you are always trading off amongst them. An experiment you can do is to taste a number of shots pulled to different yields - 1:1, 1:2, 1:3, 1:4, etc - and see what is preferred (I’d split these shots smaller and have a volunteer who doesn’t mind getting too jazzed to help taste). Note shots also change taste from top to bottom so that can be confusing as well. Another method is to line up multiple glasses and catch different parts of your extraction (say run the pump for 60s and swap over every 15s). Don’t worry about the overall time, you want extremes to get a clear understanding of what is going on.

The 2:1 in 27-33s orthodoxy assumes that the coffee is best suited to that yield (I interpret that as traditional espresso blends with darker flavour) which may not suit a bean with different characteristics. Feel free to have a play to see what gets you the best flavour, however you may conclude that the bean you are using doesn’t give you the espresso you want and that is ok too.

If you’re noticing sudden changes in the flow out the puck then it may well be fracturing as a result of grinding too fine. Back off the grind and if the shot goes sour then consider a larger yield to get back to tasty extraction.

PMA all day!

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