# Understanding pre infusion



## ting_tang (Jul 26, 2020)

Hi!

I have a PIDed Gaggia classic with a dimmer mode. Kinu Phoenix grinder. I use WDT and make a tamping with fingers, pretty light tamping

I'm experimenting with Ethiopian beans, light roast, roasted 10 days ago. Want to figure out the best scenario to use the pre-infusion.

What I'm doing at the moment:

1. WDT

2. 2 hands fingers tamping

3. Turn on the pump, with dimmer at 2 bar static position. first drop comes in 20 seconds.

4. Ratio 1:2.5 (18 in, 45 out) in 40 seconds total (20 seconds pre-infusion + 20 seconds). Temperature is 93C.

2 days ago I have been getting preеty sweet shots, acidity was dominating, but floral notes were easy recognizable.

I store beans in airscape. Today's shots quality decreased, even though I am in a close timeframe, 18-20seconds, until first drop with a low pressure, and 38-40 seconds in total.

High acidity, much less flavor.

Tried to go finer, flavor decreased again, tried to go coarser, too acidic.

I have a few questions:

1. What is the best practice for a pre-infusion, I know most machines do pre-infusion for 5-10 seconds only, without waiting until first drop? Is it the root cause?

2. Does tamping pressure impacts? Without pre-infusion finger tamping has been working good enough, I had a stable repeatable shots with a medium roasted beans. I tried to tamp harder today, didn't notice much difference.

3. When you count shot time with a pre-infusion, how pre-infusion affects it?

What would you recommend?

Thank you!


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## newdent (Feb 20, 2021)

I'm new to espresso, so can't give you any concrete advice but I am interested in this topic, so will give you a bump in hopes some more experienced people can comment!

Have a read of this paper, I thought it was interesting; https://towardsdatascience.com/espresso-parameters-pre-infusion-pressure-and-water-temperature-f543a3c4044e

First drop after 20 seconds sounds like a long time for the puck to saturate compared to what I experience using a medium/dark roast but perhaps 20s is normal for a light roast. I also thought that higher temps are usually required for better extractions in lighter roasts due to the coffee being harder to dissolve?

I'm using a cafelat robot and grinding finer than my pumped machine and I find that the puck is saturated and starting to produce a few drops after about 5 seconds at 2.5 bar (18g dose). With a longer pre-infusion, I've found that the shot can taste both under and overextracted as to have such a long pre-infusion, you must grind finer and then the shot time is inevitably too long if you're trying to achieve a specific ratio that is.

I'm trying to experiment with stopping the shot on blonding instead of waiting for a certain ratio to be met with scales. I think that shooting for a particular ratio is fine but if the shot blondes at 15 seconds but you only have 25g in the cup but were aiming for 34g, you're better to end the shot early and just accept it's going to be different to what you wanted but still be tasty and not overextracted as it would be if you continued to 34g. This article was a good read on the subject; https://www.meticulist.net/blog/improving-espresso-stopping-shots-at-the-blonding-point-instead-of-time which led me to read the referenced article here; https://www.home-barista.com/espresso-guide-good-extractions.html That's not to say that you can't tweak parameters to ensure you end up with a ratio you want but this is useful info for when everything isn't going to plan as things happen. Unexpected channelling, saturation occurring quicker than normal, etc.

If you watch the youtube videos \ read articles from the decent coffee machine makers, there's a lot of talk about theory, which if you're into all that, is very interesting and food for thought!


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## The Systemic Kid (Nov 23, 2012)

ting_tang said:


> I have a few questions:
> 
> 1. What is the best practice for a pre-infusion, I know most machines do pre-infusion for 5-10 seconds only, without waiting until first drop? Is it the root cause?
> 
> ...


 With medium plus to darker roasts - pre-infusion times tend to be shorter, i.e. in the 5-7 sec ballpark until first drops appear.

Tamping pressure doesn't have much impact on overall extraction.

Total shot time is from when you activate the pump and includes pre-infusion time.

You don't mention what level of roast you're using but the comments on acidity suggest a lighter roast? You are using a conical hand grinder which, IMO, is going to be a challenge to dial in when using lighter roasts as per your experience.


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## newdent (Feb 20, 2021)

The Systemic Kid said:


> With medium plus to darker roasts - pre-infusion times tend to be shorter, i.e. in the 5-7 sec ballpark until first drops appear.
> 
> Tamping pressure doesn't have much impact on overall extraction.
> 
> ...


 He does mention he is using a lighter roast.

Are you suggesting that dialling in will be a pain because it's a hand grinder or because the burrs are conical out of interest? I have a niche on order and am hoping the conical burrs will be OK for all roasts but plan to alternate shots between the niche and 58mm flat burrs for a while to see if I notice any taste difference between the two.


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## ting_tang (Jul 26, 2020)

Thanks for your reply.



The Systemic Kid said:


> comments on acidity suggest a lighter roast?


 Correct.



The Systemic Kid said:


> is going to be a challenge to dial in when using lighter roasts as per your experience


 Will take that into account, thank you.

After making some investigation, I came to kind of acceptable results.

1. Increased to a standard tamping, but not too hard, 10-15lbs probably. (Before: finger tamping, pretty light)

2. Increased the pressure of pre-infusion. I have not pressure gauge attached to the pump, so marked on the dimmer 3-4barish with static pressure. (Before: 2bar static).

3. Pre-infusion time is now a static variable, I keep 10 seconds of pre-infusion. (Before: was waiting until the first drop appears which could happen in 15-22 seconds)

4. Increased temperature to 94.5C, I noticed the most significant impact with that. (Before: 93C)

5. Went coarser, looks like I went too fine during the dial in as further finer has been reducing the extraction level, less and less taste. (before with 20 seconds pre-infusion until the first drop, I had 40-45 seconds shot time, now with 10 seconds static I have 33-35 seconds shot time).

It's still a bit unbalanced, acidity is bright (probably that is just a beans), but much better in a milk drink.


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## ting_tang (Jul 26, 2020)

newdent said:


> This article was a good read on the subject; https://www.meticulist.net/blog/improving-espresso-stopping-shots-at-the-blonding-point-instead-of-time which led me to read the referenced article here; https://www.home-barista.com/espresso-guide-good-extractions.html That's not to say that you can't tweak parameters to ensure you end up with a ratio you want but this is useful info for when everything isn't going to plan as things happen. Unexpected channelling, saturation occurring quicker than normal, etc.


 Sorry, I missed your comment before posting my previous comment. Thank you! I read those articles before, but have read again during the investigation. But main conclusions I got in the Scott Rao's book, Espresso Extraction: Measurement and Mastery.



newdent said:


> I'm trying to experiment with stopping the shot on blonding instead of waiting for a certain ratio to be met with scales


 I tried that before having the dimmer mode, I drink mainly a milky drinks (80% of time), I found that with stopping the shot on reduces 'brightness', but have to try it again. Thanks for pointing.



newdent said:


> With a longer pre-infusion, I've found that the shot can taste both under and overextracted as to have such a long pre-infusion, you must grind finer


 Indeed, going finer doesn't mean increase of extractions, I think there is a zone, after which extraction stops increasing, even with a long pre-infusion.


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## The Systemic Kid (Nov 23, 2012)

newdent said:


> He does mention he is using a lighter roast.
> 
> Are you suggesting that dialling in will be a pain because it's a hand grinder or because the burrs are conical out of interest? I have a niche on order and am hoping the conical burrs will be OK for all roasts but plan to alternate shots between the niche and 58mm flat burrs for a while to see if I notice any taste difference between the two.


 Hand grinding for espresso is OK but not something I'd want to do as a go to option. And hand grinding lighter roasts for espresso is even more of a pain.

I've put same beans through a Niche and an EKs. Niche held up very well and produced good results with lighter roasts but couldn't hit the sweet spot the EKs could.


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## Rob1 (Apr 9, 2015)

ting_tang said:


> Hi!
> 
> I have a PIDed Gaggia classic with a dimmer mode. Kinu Phoenix grinder. I use WDT and make a tamping with fingers, pretty light tamping
> 
> ...


 Depending on how the dimmer mod works 20 seconds might be too long. If the dimmer mod limits the pressure the pump can achieve but doesn't slow flow rate down until you approach/hit this pressure then it should be fine, but if the dimmer decreases flow rate you're probably waiting a long time for the headspace above the puck to be filled. If that's the case, better fill that space quickly and turn the pump down before pressure builds so you get the gentle pre-infusion, at least that is my experience with the paddle on an e61 that alters flow.

Shot times don't matter too much really, they're good to know for consistency but you can't really judge a shot from it. I've used pre-infusion from 10-20 seconds, and total shot times of anywhere between 35 and 70 seconds, yield has a much greater impact, there's no rule about shot time. Of course if you're grinding way too fine and you're channelling it's going to be bad.

You also can't judge a shot from blonding as it's really just judging the colour of the crema which varies based on roast, it has nothing to do with extraction. Flow rates are more telling, a flow rate rapidly increasing is probably best to end the shot or decrease your flow if you can. Flow rates always increase through a shot but if it seems to happen very suddenly that's bad. I don't like to see it speed up too much and sometimes it's necessary to use the paddle, but sometimes a coffee will just hold up well through the extraction at full pressure without speeding up too much towards the end. Shots are still dialled in with yield and grind adjustments.

Also pre-infusion ends when the first drops appear, it doesn't matter what pressure that happens at.

You probably aren't over extracting, just discovering the limits of your grinder.


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## ting_tang (Jul 26, 2020)

Rob1 said:


> better fill that space quickly and turn the pump down before pressure builds so you get the gentle pre-infusion


 So water should do pre-infusion without pressure from the pump? Just with a gravity?



Rob1 said:


> I don't like to see it speed up too much and sometimes it's necessary to use the paddle,


 And with a reduced flow, you try to keep the same yield?


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## The Systemic Kid (Nov 23, 2012)

ting_tang said:


> So water should do pre-infusion without pressure from the pump? Just with a gravity?


 Pre-infusion was held to mean saturating the puck prior to it being hit with the full force of the pump or lever spring pressure. As a rule of thumb, pre-infusion ends when the first drips appear in the cup prior to the puck being hit with full pump force. That said, some machines offer pre-infusion pressures of up to six bars.


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## ting_tang (Jul 26, 2020)

The Systemic Kid said:


> As a rule of thumb, pre-infusion ends when the first drips appear


 Sorry if I'm understanding wrong, does that mean if you don't see the first drips, pre-infusion is not completed or has not been not done properly? In most machines pre-infusion is timed, and you may not be able to control it, but still they have it. Should I aim to get the first drops in first 10 seconds (for example) via dimmer adjustment or first drop time can be variable, and I just need to wait it in context of my current grind settings with a 'constant' setting of the dimmer?


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## newdent (Feb 20, 2021)

The decent guys seem to advocate 3 bar pre-infusion, stating that getting some compression during is important. I don't think pre-infusion with no pressure is a thing, it would likely take a long time to saturate the puck. I'm just speculating on that though, I'd love some in depth explanations of it all.


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## newdent (Feb 20, 2021)

ting_tang said:


> Sorry if I'm understanding wrong, does that mean if you don't see the first drips, pre-infusion is not completed or has not been not done properly? In most machines pre-infusion is timed, and you may not be able to control it, but still they have it. Should I aim to get the first drops in first 10 seconds (for example) via dimmer or first drop time can be variable, and I just need to wait it in context of my current grind settings with a 'constant' setting of the dimmer?


 I think pre-infusion being a fixed time would indicate a limitation with the machine as pre-infusion is evenly saturating the puck prior to applying full pressure according to my understanding. I use a mirror to view that the bottom of the basket is evenly saturated and then apply full pressure.

Edit - I do wait for a drop to hit the cup but in my mind, I think the point is that the puck is saturated enough that flow will begin as soon as you apply full pressure.

I think decent videos indicate that flow increasing over the the duration of the shot is normal as the puck progressively releases less coffee, so increased flow is required to compensate. Obviously not massively large increases but he said that flow should be trending upward.

The main take home for me is that it seems like there's still lots to be learned and nothing is set in stone!


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## ajohn (Sep 23, 2017)

I've been messing with infusion power, you might say with the same grinder setting in as much that it may be changed by rather small amounts for the usual reason.

I set infusion time to 15sec the max I can use and power to obtain drips throughout that. This with my usual grind setting. Ratio didn't change as much as I though it would still using a 30sec shot. Going on taste and colour of the flow yield had increased a lot. This with my usual dark roast. One odd thing is that ratio no longer had as much effect. I can usually make the bean truly sweet right through to monsooned's version of bitter. Feel I may need to try different shot times with it.  Nice strong drink though but I prefer it to have a bit more edge.

The lower power resulted in the pump stalling. Due to the stalling i cut infusion time down to the default which I think is 7secs  I'd need to look. The pump stalls very briefly before full pressure kicks in. Conclusion from taste, the extra 8secs was pointless.

Same set up, 2 medium roasts and one light. No real problems tuning them but suspect I am using somewhat lower ratios than I usually use. On these beans the pump hasn't stalled. Just drips until full power kicks in, maybe a tiny amount of flow.

All grinder setting changes have been very small even on Niche. One problem has been shot time consistency. Suppose the puck is being stressed more so more work on prep and getting better. I usually use a fixed 30sec shot and expect very little change in output. Odd ones may vary more but not that often.


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## The Systemic Kid (Nov 23, 2012)

ting_tang said:


> Sorry if I'm understanding wrong, does that mean if you don't see the first drips, pre-infusion is not completed or has not been not done properly? In most machines pre-infusion is timed, and you may not be able to control it, but still they have it. Should I aim to get the first drops in first 10 seconds (for example) via dimmer adjustment or first drop time can be variable, and I just need to wait it in context of my current grind settings with a 'constant' setting of the dimmer?


 Pre-infusing to first drips is rule of thumb. It indicates the puck is fully saturated. There isn't, as far as I am aware, gospel evidence on length of time needed but it's going to be affected by the degree of grind - going finer will require longer pre-infusion. I wouldn't get too preoccupied with PI time length. What matters is what it tastes like.


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## ajohn (Sep 23, 2017)

The Systemic Kid said:


> Pre-infusing to first drips is rule of thumb


 Maybe even drips come flow across the entire base of the basket??


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## MWJB (Feb 28, 2012)

ajohn said:


> Maybe even drips come flow across the entire base of the basket??


 It's certainly almost, very nearly over when you have a full weight of drink in the cup 

I'm not sure there's much facility in going down a rabbit hole of identifying the moment preinfusion ends. It can allow a finer grind & the longer you preinfuse, the faster your shot will flow during the remainder of the shot time. Beyond that I'm not sure there's much to add, outside of specific machines/practices with unusual parameters.


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## Rob1 (Apr 9, 2015)

ting_tang said:


> So water should do pre-infusion without pressure from the pump? Just with a gravity?
> 
> And with a reduced flow, you try to keep the same yield?


 No, what I'm saying is pre-infusion ends when you see the first drips regardless of pressure. Pressure doesn't build until the headspace above the puck is filled. The longer it takes to fill the headspace, the longer it takes for pressure to build up, and the longer the coffee is sitting there absorbing water and expanding before you hit it with pressure whatever pressure your pump can reach at the flow rate you've set (assuming your flow rate is affected?). In my experience this can be very bad, I want to see some low pressure quite quickly to prevent the puck from expanding. So when I said 'fill the headspace quickly and turn the pump down' I meant basically turn it on to full speed for a little less than how long it wold usually take to fill the headspace and then turn it down to whatever pressure (or flow=pressure) you want the pre-infusion to occur at. Whatever pressure you choose to use pre-infusion will end when you see the first drips, so if you go down to 2 bar for 10 seconds and then up to 9 bar and it's another 5 seconds until first drip your pre-infusion was 15 seconds between 2 and 9 bar.

I'll dial in to whatever I think is best for yield and don't keep the same ratio for different coffee. I might alter yield but generally dialling in will be done with the ratio, then flow, then tweak the ratio if I think it will be better with less or more.


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## ting_tang (Jul 26, 2020)

Rob1 said:


> I might alter yield but generally dialling in will be done with the ratio


 Just to confirm, if you notice flow increasing rapidly at some point of extraction, you reduce the pressure, to keep the flow in a 'normal' speed, and that will reduce over extraction?



The Systemic Kid said:


> going finer will require longer pre-infusion


 But 'no-go' zone (when you go too fine, and a lot of channeling starts to occur, so flow increases, extraction reduces) with going finer still apply, even with pre infusion? Or you can handle such things with a much longer pre infusion? (i.e. 25-30 seconds etc)



newdent said:


> so increased flow is required to compensate


 with a pressure reducing?


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## Rob1 (Apr 9, 2015)

ting_tang said:


> Just to confirm, if you notice flow increasing rapidly at some point of extraction, you reduce the pressure, to keep the flow in a 'normal' speed, and that will reduce over extraction?
> 
> But 'no-go' zone (when you go too fine, and a lot of channeling starts to occur, so flow increases, extraction reduces) with going finer still apply, even with pre infusion? Or you can handle such things with a much longer pre infusion? (i.e. 25-30 seconds etc)
> 
> with a pressure reducing?


 Overextraction has only been an issue if I've pulled a very long shot or if I've ground way too fine and choked the machine. You're probably getting silt rather than over extracting. Flow will increase with a long pre-infusion, especially if it just sits there absorbing water without being put under pressure. IMO, the puck probably cracks apart when this happens but I have no way of proving it without a transparent filter basket. I haven't measured the effect flow rate has on extraction, I probably should. Increasing flow should extract more I think.

I think the decent thing quote is basically saying flow rate increases as the puck is eroded and an increasing flow rate is required to maintain pressure.


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