Pre-infusion using flow control vs. pre-wetting

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Ursego

#1: Post by Ursego »

The flow control beginner continues to torment you with questions! :lol:

I have read more than once that pre-wetting (which is when drops drip from the group head by the force of gravity when the pump is not running) is not serious, and that real pre-infusion is only under 2-3 bar pressure created by a running pump using FCD (or under water line pressure on plumbed machines).

Check out this video fragment:

http://www.youtube.com/watch?v=HOgRIdLib24 ?t=74 [remove the space before the question mark]

This video helps to find the flow control position for pre-infusion. This position should give a flow of 1.6 g/sec (50 g of water in 30 sec). That is exactly the flow rate of my ECM FCD when the faucet knob is turned to 1/8.

I just measured the flow rate of my ECM Puristika at pre-wetting (when the pump is not running yet, but the timer is already counting). I got 1.7 g/sec. This is the same as the recommended flow for FC pre-infusion (even slightly higher). So why is pre-wetting considered worse than pre-infusion? If it's the same flow rate, what difference does it make how it was created?

When using pre-wetting, I noticed that the first drops appear at the bottom of the basket after 17-19 sec. That is, in that time, the puck has been wetted all over its height, which is what we are aiming for to avoid unevenness (to be 100% sure, you can wait more, making the total pre-wetting time 25 sec). Why is the ability to make Slayer shots described as an advantage of flow control? Can't any E61 owner pull them?

PIXIllate
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#2: Post by PIXIllate »

The goal is to saturate the entire puck AS QUICKLY AS POSSIBLE.

A "Slayer" style "slow and low flow" wetting of the puck has been fairly thoroughly debunked as the optimal way to preinfuse.

In other words, you want to introduce roughly 2-2.5 times the weight of your dry dose (coffee) in water in the shortest time possible. An 18g dose would want to have roughly 40-45g of water introduced in under 10 seconds. At that point the goal is to keep the pressure under 4 bar while you soak or "Bloom" the puck. Once you have dripping you have saturated the puck (which, in order to do efficiently requires pressure) and can move on the the extraction phase.

Again, I tried to offer a more complete explanation in the thread with the video. Practice this technique and you'll begin to get a feel for what I'm explaining above.

An Even MORE Considered Approach to E61 Flow Control (now with video)

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Jake_G
Team HB

#3: Post by Jake_G »

There are a couple things at play here.

The relationship between flow rate and pressure is tenuous when you've got a FCD at play.

Let's start with the "pre-wetting" flow:
Pre-wetting is just opening up the brew group to whatever pressure may or may not be within the boiler. With an HX machine, the HX is maintained at the same temperature as the service boiler, which will induce the same pressure as the service boiler, which is the saturation pressure of the steam in boiler. In your case, you have a single boiler machine, so the pressure in the boiler is... complicated.

If the offset on your PID has the boiler temperature higher than the local boiling temperature at your elevation, you will have some pressure within the boiler, which can be looked up in a table. In this case, when you crack the lever, the temperature of water will cause it to flash boil and this will cause a little bit of pressure. Depending on the temperature of the boiler, this could be a few psi, or possibly zero. It all depends on the offset in the PID.

Now, since you have a boiler with no air in it, when the heating element kicks on, that water will want to expand and when it does, it will generate lots of pressure. In fact, if it weren't for the OPV venting the pressure from the boiler, it would burst from the expansion pressure. So that's why I say it's complicated. You will have lots of pressure from expansion when you first crack the valve but that pressure will dissipate almost immediately, leaving you with a few psi, which is likely 0.1 or 0.2 bar. Not much.

Flow control set to the same flow rate as your "pre-wet" flow is totally different, because you have the full pressure of the OPV acting behind it. It will take a long time to build pressure. But it will. The pre-wet will not. It simply can't build pressure that it doesn't have. But with the FCD, your pump is running, so theres no problem ramping up to you pump pressure eventually.

So pre-wetting just sort of makes the puck wet, but the same flow rate set with the pump running will drive that water into and through the puck. This is much more effective. Then there is the approach of actually setting a preinfusion pressure that is less than your final brew pressure and holding it there until you get some drips from the group. Thos emulates line pressure and is yet another approach. Some prefer line pressure over Slayer-style slow preinfusion and others prefer the Slayer approach. It all comes down to preference.
PIXIllate wrote:The goal is to saturate the entire puck AS QUICKLY AS POSSIBLE.
Who's goal, exactly?
A "Slayer" style "slow and low flow" wetting of the puck has been fairly thoroughly debunked as the optimal way to preinfuse.
False.

There is no "optimum" way to preinfuse. There are different ways that yield different results that cater to specific preferences. I've tried both ways and I find both have their merits.
In other words, you want to introduce roughly 2-2.5 times the weight of your dry dose (coffee) in water in the shortest time possible. An 18g dose would want to have roughly 40-45g of water introduced in under 10 seconds. At that point the goal is to keep the pressure under 4 bar while you soak or "Bloom" the puck. Once you have dripping you have saturated the puck (which, in order to do efficiently requires pressure) and can move on the the extraction phase.
There is nothing wrong with this approach, but there is also nothing about it that makes it more right than any other approach. If the OP tries this and loves it, then yes. That's what they want. But if they want something else... that's what they want. It sounds like this is what you want, which is totally fine.
Again, I tried to offer a more complete explanation in the thread with the video. Practice this technique and you'll begin to get a feel for what I'm explaining above.

An Even MORE Considered Approach to E61 Flow Control (now with video)
You're approach is totally sound, and is one I have used quite a bit and the OP should give it a try - if they want to - it seems like right now they are experimenting and learning fundamentals, rather than copying a specific technique. Flow control devices offer a great deal of flexibility so there is no reason to force a specific technique.

Cheers!

- Jake
LMWDP #704

PIXIllate
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#4: Post by PIXIllate »

Jake_G wrote: There is no "optimum" way to preinfuse. There are different ways that yield different results that cater to specific preferences. I've tried both ways and I find both have their merits.

- Jake
I think here we fundamentally disagree. It's my belief that there IS an optimum way to preinfuse. I also think it's more constructive (especially for beginners) to follow a specific technique until they start to get some first hand experience with the ways flow and pressure interact with a needle valve. I know I wish I'd had some better guidelines to follow as I was figuring it all out for myself.

Please let me be clear, I know you're speaking from a position of great experience and understanding. I'm not saying you don't have a point that some people with some equipment and some coffees may have a personal preference for a Slayer style preinfusion. That can be true.

I just beleive there are more and less efficient techniques for extracting coffee. If you're using easily soluble coffees that may have intrinsic roast flavours you don't want in your cup then you may want to use a less efficient technique. For me personally I've tried both ways and have never prefered the taste in the cup of the low and slow method.

vit

#5: Post by vit »

I do believe that there is more or less optimal way for preinfusion (and extraction) for particular combination of coffee, machine, grinder and personal taste

However, I think that those optimal ways differ quite a bit depending on each combination of above

On my combination, shots seem to be the best when using about constant or slightly decreasing flow for PI until first drop and then raise to brew pressure. Didn't find advantage of decreasing pressure toward the end either. So my optimum seems to be different than you described

Where are slayer type shots actually debunked ?

How do we know PI pressure 4 bar is optimum? Some people are using as low as 0.5 bar

Also, most "constant flow" preinfusion machines actually don't have constant flow of water into puck, because as pressure in basket is rising, pressure difference on the valve is decreasing, so flow actually DECREASES (in addition that inflow into the puck is lower at the beginning because air above the puck has top be compressed) - exception being DE1 (flow is measured by pump, however remark about compressing air is still valid) and some lever machines (if you decide to use constant piston speed which would be constant flow) and maybe there are some other ...

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Jake_G
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#6: Post by Jake_G »

PIXIllate wrote:I just beleive there are more and less efficient techniques for extracting coffee.
Indeed there are.

But please remember that efficiency does not equal personal preference. This would be akin to someone asking which car is the most fun to drive and then someone pointing them towards the vehicle with the best fuel efficiency, claiming that it is objectively true that the more efficient car is the most fun to drive. Then the circular reasoning kicks in protecting that POV: "You can drive further on a gallon of gas, thus the area under enjoyment curve is greater. IT'S SCIENCE!" It is very clear that your opinion supports the extraction science model of efficiency as being best for flavor. But please note that the OP has asked multiple questions along their journey and mentioned that they prefer darker roasts. Probably even even roasts that taste roasty. They have also demonstrated that their learning style is one of research followed by asking clarifying questions.
vit wrote:Also, most "constant flow" preinfusion machines actually don't have constant flow of water into puck, because as pressure in basket is rising, pressure difference on the valve is decreasing, so flow actually increases (in addition that inflow into the puck is lower at the beginning because air above the puck ačsp has top be compressed)
Actually, the flow rate into the puck decreases as the pressure increases. In fact, the reason the pressure increases is because the flow decreases. Remember that pressure drop across a valve is proportional to the square of the flow. If your water debit is 4ml/s at a pressure drop of 9 bar (9 bar at the pump, zero at the shower screen/puck), then when the flow is 2ml/s, the pressure drop will only be 2.25 bar (meaning 6.75 bar present at the puck). The beauty of the flow control device is that you can change this relationship by adjusting the valve, but if you leave the valve fixed, the flow will always decrease as the pressure at the puck increases.

Also, the air above the puck does not reduce the flow rate of the water into the puck. Not sure where you're getting that info. Water inrush occurs unimpeded at whatever the water debit is set to until the puck begins resisting the flow. It is at this point, when the water forms a liquid seal at the top of the puck, that whatever remaining air in the brew chamber begins to compress, and this can occur as soon as the flow rate exceeds the wicking rate of the puck. There is some evidence that suggests 4ml/s is about the peak that a dry puck can absorb without generating pressure. I suspect this is highly dependent on the anatomy of the puck in question, but something in that range certainly passes the sniff test. Flow higher than this wicking rate can build pressure prior to the puck being fully saturated, and this is why preinfusion is a thing.

Back in the early aughts, when 30ml/s Lineas reigned supreme, overstuffed baskets with coarse grinds were the recipe for success. Levers, of course were still doing things the old-fashioned way, with a massive flow rate that was limited by the boiler pressure (or line pressure in cold-fed HX machines). Overstuffed baskets with coarse grinds never worked well with those machines, and folks were quietly enjoying much more nuanced beverages for years before the Slayer came out and much later the DE1. Whether you limit the flow or the pressure, both allow the puck to absorb more water before it is brought to full pressure and both allow for completely different type of extraction than a full-flow shot that brings the puck to full pressure before saturation.

It's also important to remember that pretty much any machine with a reasonably sized gicleur has a slow ramp to brew pressure and enjoys a portion of this phenomenon every time you pull a shot.

I'm rambling again, so I'll stop there.

Cheers!

- Jake
LMWDP #704

Pressino

#7: Post by Pressino »

vit wrote:
How do we know PI pressure 4 bar is optimum? Some people are using as low as 0.5 bar

Also, most "constant flow" preinfusion machines actually don't have constant flow of water into puck, because as pressure in basket is rising, pressure difference on the valve is decreasing, so flow actually increases (in addition that inflow into the puck is lower at the beginning because air above the puck has top be compressed) - exception being DE1 (flow is measured by pump, however remark about compressing air is still valid) and some lever machines (if you decide to use constant piston speed which would be constant flow) and maybe there are some other ...
I think the idea that 4 bar is an "optimum" pre-infusion pressure comes from the fact that the traditional e61 "pre-infusion" springs were set to roughly that level (actually just a bit lower than that). The original FCDs left the "standard" e61 spring in place, but later they were replaced by a stiffer spring with, I believe, the intent to defeat the old style e61 pre-infusion and allow folks to use whatever flow/pressure profile they want all the way through extraction.

BTW, it seems to me from reading comments on the use of e61 FCDs here and in other threads that many still do not understand exactly how these gadgets work to regulate flow and pressure (and specifically the relationship between the two variables) during extraction with a coffee puck in place in the portafilter basket.

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Peppersass
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#8: Post by Peppersass »

I tasted an improvement when I went from the Slayer recommended preinfusion flow rate to the faster one favored by Decent owners. However, I suspect that it's not so simple as a faster preinfusion rate saturating the puck more thoroughly.

For one thing, I had to grind a little coarser when I went to the faster preinfusion rate. That changed the taste in the cup. Turns out I liked the change, so I kept the faster preinfusion flow rate.

But here's the catch: I pull singles. The puck is much thinner and smaller that an 18g puck, and there's a ton more headspace. I seriously doubt that the Slayer preinfusion flow rate didn't fully saturate my single pucks before max pressure was reached.

Honestly, I'm not sure why the faster preinfusion flow rate tastes better. It could be that with the finer grind and longer contact time the coffee was over-extracting. Or, maybe the puck was loosening too much and the coffee was under-extracting. I somewhat favor the former, though many believe it's not possible to over-extract a light roast (I'm not one of them.)

Another data point is that I tried Chris's method without the soak (I need to do some programming to implement that), and didn't like the resulting shot at all. It seemed over-extracted, so a soak probably would have made it worse. Perhaps the reason is that Chris designed his method for doubles, not singles.

Bottom line, I don't believe there's a preinfusion flow rate/technique that's optimum for all machines, all coffees and all input parameters. There are a lot of moving parts in espresso extraction.

PIXIllate
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#9: Post by PIXIllate »

Jake_G wrote:Indeed there are.

But please remember that efficiency does not equal personal preference. This would be akin to someone asking which car is the most fun to drive and then someone pointing them towards the vehicle with the best fuel efficiency, claiming that it is objectively true that the more efficient car is the most fun to drive. Then the circular reasoning kicks in protecting that POV: "You can drive further on a gallon of gas, thus the area under enjoyment curve is greater. IT'S SCIENCE!" It is very clear that your opinion supports the extraction science model of efficiency as being best for flavor. But please note that the OP has asked multiple questions along their journey and mentioned that they prefer darker roasts. Probably even even roasts that taste roasty. They have also demonstrated that their learning style is one of research followed by asking clarifying questions.

- Jake
It's nice that there's a place on the internet where two people can both understand one another and disagree while knowing the other person is also right, in a certain way. Thanks to Jake for offering another valid perspective and approach.

What seems to me to be missing is a more complete presentation of the physical steps/mechanics of different, technically sound, profiles using an e61 flow control. You really need to spend some time using one profile in a very structured way to start to get a feel for how flow and pressure interact and the timing required to get them both to land where and when you want. Otherwise you can easily spend a lot of time messing around and not really building anything.

My approach is at least a well defined starting point (especially for beginners) where they can aim for a technically sound extraction goal with enough steps where you can't help but start to see how flow creates pressure and then how pressure restricts flow. If you master what I presented and the reasoning behind each step then you are in a good place to decide what you like or don't like about it and strike off in a different direction from there. But this time a person can do it in a more controlled, focused way. As you said, a flow control is a VERY versatile device. So much so that it can be completely overwhelming to a person starting out in the absence of some guidance. At least I know I felt that way for awhile.

Peppersass wrote:Another data point is that I tried Chris's method without the soak (I need to do some programming to implement that), and didn't like the resulting shot at all. It seemed over-extracted, so a soak probably would have made it worse. Perhaps the reason is that Chris designed his method for doubles, not singles.
This is absolutely correct Dick, I never pull singles and about 95% of my shots are currently between 17.5-18.5g with an 18G VST.

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Jake_G
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#10: Post by Jake_G »

PIXIllate wrote:It's nice that there's a place on the internet where two people can both understand one another and disagree while knowing the other person is also right, in a certain way.
Amen to that!
LMWDP #704