I recently bought a Linea Mini, and the the operation of it is taking some adjustment coming from my old machine...

Is anybody here familiar with how exactly the brew pressure gauge registers its reading (where at?)? If the machine is off, its at 9 bars. If I turn the brew paddle on with no portafilter in the machine and just let water rush out, it's at 9 bars. If I grind my beans so fine and tamp it so hard that espresso barely drips from the portafilter, its at 9 bars. If I grind very coarse and barely tamp it so espresso rushes out fast, it's at 9 bars. Why 9 bars all the time no matter what? I can't gauge my grind or my tamp by reading the pressure like I used to on my old machine. With my old machine, if my grind was too fine, the pressure would be too high. If it was too coarse, the pressure would barely be 7 or 8 bars, so I could use that as a way to adjust my variables until I hit 9 bars. With the Linea Mini, it's always 9 bars no matter what. It makes me wonder if this is just a water pump gauge and not an actual brew gauge showing the pressure at the brew head like I thought it was? If so, what the point of a water pump gauge instead of a brew gauge? The manual says it's a brew group gauge, so idk...

Also on page 24 of the manual it says the steam boiler is set at 2 bar from the factory, but mine never gets above 1.5.

On a different note, water rushes out of this thing so fast when I flip the brew paddle, and the pre-infusion is almost non-existent. I read that it's two seconds set from the factory, but it's like a fire hose the instant I flip the brew paddle The first two seconds is no different than what follows it.

I can't lie... This machine is sexy to me, but I'm mildly wishing I had bought a Slayer instead (which was the other machine on my short list), but I'm hoping that feeling will subside soon. I've only pulled about 15 shots on it and the thought of selling it and buying a Slayer is already in the back of my head

I'm coming from a Breville Dual Boiler (lol) for the last couple years and I'm fairly unimpressed with the Linea Mini.

The pressure is always 9 BAR because the LMLM uses a rotary pump with a bypass valve that's adjusted to produce 9 BAR at the gauge. The primary producer of this pressure is the 0.8mm gicleur (flow restrictor) that's in the brew boiler path. The gicleur is always in the path, which is why you see 9 BAR of pressure even at free flow (no puck.) If the gicleur wasn't there, you'd see zero pressure on the gauge during free flow.

I'm not familiar with the exact architecture of the LMLM, but since you always see 9 BAR of pressure the gauge must be positioned before the gicleur (as it is in my GS/3), so it's really measuring brew boiler pressure, not the pressure at the puck, which is after the gicleur.

Note that the pressure is greater than that produced by the gicleur with a puck in place, and it's much greater when you use a blind basket for backflushing. But the boiler pressure remains at 9 BAR because the bypass valve on the pump transfers the excess water back to the input, thus maintaining constant boiler pressure at the desired setting of 9 BAR.

FWIW, when the pump is adjusted to 9 BAR free flow on a GS/3, the boiler pressure will rise to about 10 BAR when pulling a shot. However, measured pressure at the puck will be 9 BAR. I believe this is because the gicleur is a little smaller than the LMLM-- 0.6mm and it causes a pressure drop of about 1 BAR.

The Slayer has a 0.7mm gicleur, but its gear pump doesn't have a bypass valve. As a result, its boiler gauge will show different pressures during brew, free flow and backflush. In fact, as the puck becomes more permeable later in the shot, you'll see the boiler pressure decline to about 7 BAR, depending on the grind and dose.

Actually, I've traced out and drawn a complete schematic of the water circuit, including all 4 check valves and the pre-heat, cold water bypass and everything.

First - the easy question: Steam boiler pressure is adjusted to 1.3-bar on US models. The manual is translated from the Italian model and says 2.0 bar. You can adjust the pressure stat if you need it higher, but that seems a completely adequate pressure. I think it likely that all 120v models are adjusted to 1.3-bar at the factory.

The brew hydraulic circuit is quite complex in the LMLM. The brew pressure gauge does not measure the actual pressure at the puck. It measures the pressure inside the brew boiler that is integrated into the brewgroup. The brew pressure is measured at a 4-way cross fitting, which leads into the brew boiler.

When the machine is idle, the brew pressure gauge should indicate 12-bar. There is a pressure relief valve just behind the drip tray that can be adjusted to maintain this pressure. It should be adjusted so that at idle, the pressure does not exceed 12-bar, but should be right at or just under that value. You can adjust it easily with a wrench (17mm as I recall) or even with your fingers if it isn't hot. Adjust, flush water with the brew padle for a second or so, then watch the pressure after you turn off the brew paddle. It should quickly rise and settle at 12-bar. It should hold this pressure for a considerable amount of time, like 30-minutes or longer. (if it doesn't hold the adjusted pressure for long, then a check valve or something is leaking and you should contact LM for service - they were quite helpful when I had a check valve go bad and the indicated pressure would drop in a short time idling).

I've found that the idle pressure is an important setting on the LMLM, as it greatly effects the next thing you mentioned, pre-infusion.

The pre-infusion time on the LMLM is fixed at 1-second. When you activate the brew paddle, the first thing that happens is the brew solenoid valve opens, releasing pressure in the brew boiler to the brew head. You'll notice that the brew pressure gauge drops to 0-bar as soon as the valve opens. There is a 1-second delay before the pump is powered. This is the pre-infusion period, and you won't get good pre-infusion unless the brew boiler is idling at the correct pressure and the brew group has been recently used or primed (with a quick flush of water from activating the brew paddle).

The rotary pump on the LMLM is very high volume and it will quickly regain pressure, as you'll notice when watching the brew pressure gauge.

The brew pressure gauge however, will not indicate at all what the brewing pressure at the puck is. To measure the actual brewing pressure, you'll need a tool, like a SCACE-II device. The brewing pressure is adjusted on the pump body with a nut and bolt.

Unlike some internet lore, I assure you that the SCACE-II is required to actually measure and set the brew pressure on pretty much every machine out there. I did some experiments with my e61 which conclusively proved to me that was the case.

I did change the 0.8mm orifice (aka jet or gicleur) to a 0.6mm which is available from LM parts. There was a big thread on that subject some months ago. It does change the rate at which water flows out of the brew boiler, and has some side effects like slowing the rate at which pressure rises in the brew head. It has a side effect of altering the final pressure - which means you just have to re-calibrate with the SCACE to really know the brew pressure. Honestly, I don't think it made a lot of difference.

The LMLM is calibrated quite well at the factory, at least mine was. It produces very, very consistent temperature and pressure at the brew head. I've measured this enough times with the SCACE to be very confident in that.

All in all, it is a very good machine. It doesn't have lots of adjustable parameters for tweeking. It does what it is intended to do, stably and repeatably and produces very consistent coffee, shot after shot.

A G/S-3 MP, or a Slayer does offer more widgets to adjust. But a thing you can control often turns into a thing you must control. Pre-infusion can screw up a shot, just as much as it can make them better sometimes.

Part two - gauging your grind:

The pump in the LMLM (as would be true in the Slayer or any other commercial/prosumer rotary pump) has enough volume capacity that you can't estimate your grind by the gauge at all, as you might have done on the Breville with its low-volume pump.

The preferred way to gauge your grind setting is by time and weight, especially on the pro machines.

Pull your shots by weight, by putting a scale on the drip tray and the shot glass or cup on it. Start a shot timer (ie, stopwatch on your phone or whatever) the moment you click the paddle to brew position.

I've found that if I can hit my target beverage weight in 30-32 seconds, that is kind of the sweet spot. The target is the beverage weight, the time is kind of a QC parameter check.

For instance:

Weigh 18g of beans and grind and tamp into the 17g basket. (it's OK +/- 1g from the marking)

I like a brew ratio of about 1.8:1, or about 32g of beverage for 18g dose.

Setup the cup and scale, tare the cup, start the brew switch and timer.

Stop the brew paddle when your scale approaches 32g (anticipate it a little). Stop the timer at the same time you stop the brew. Adjust the grind finer or coarser as needed so you get the desired beverage weight in something on the order of 28-35 seconds.

Dime to donuts - you'll have great shot, or pretty darn close.

From that point, you can fine dial in the dose and ratio and temperature to taste, as you'll find many great discussion about on this board.

nuketopia wrote:Actually, I've traced out and drawn a complete schematic of the water circuit, including all 4 check valves and the pre-heat, cold water bypass and everything.

First - the easy question: Steam boiler pressure is adjusted to 1.3-bar on US models. The manual is translated from the Italian model and says 2.0 bar. You can adjust the pressure stat if you need it higher, but that seems a completely adequate pressure. I think it likely that all 120v models are adjusted to 1.3-bar at the factory.

The brew hydraulic circuit is quite complex in the LMLM. The brew pressure gauge does not measure the actual pressure at the puck. It measures the pressure inside the brew boiler that is integrated into the brewgroup. The brew pressure is measured at a 4-way cross fitting, which leads into the brew boiler.

When the machine is idle, the brew pressure gauge should indicate 12-bar. There is a pressure relief valve just behind the drip tray that can be adjusted to maintain this pressure. It should be adjusted so that at idle, the pressure does not exceed 12-bar, but should be right at or just under that value. You can adjust it easily with a wrench (17mm as I recall) or even with your fingers if it isn't hot. Adjust, flush water with the brew padle for a second or so, then watch the pressure after you turn off the brew paddle. It should quickly rise and settle at 12-bar. It should hold this pressure for a considerable amount of time, like 30-minutes or longer. (if it doesn't hold the adjusted pressure for long, then a check valve or something is leaking and you should contact LM for service - they were quite helpful when I had a check valve go bad and the indicated pressure would drop in a short time idling).

I've found that the idle pressure is an important setting on the LMLM, as it greatly effects the next thing you mentioned, pre-infusion.

The pre-infusion time on the LMLM is fixed at 1-second. When you activate the brew paddle, the first thing that happens is the brew solenoid valve opens, releasing pressure in the brew boiler to the brew head. You'll notice that the brew pressure gauge drops to 0-bar as soon as the valve opens. There is a 1-second delay before the pump is powered. This is the pre-infusion period, and you won't get good pre-infusion unless the brew boiler is idling at the correct pressure and the brew group has been recently used or primed (with a quick flush of water from activating the brew paddle).

The rotary pump on the LMLM is very high volume and it will quickly regain pressure, as you'll notice when watching the brew pressure gauge.

The brew pressure gauge however, will not indicate at all what the brewing pressure at the puck is. To measure the actual brewing pressure, you'll need a tool, like a SCACE-II device. The brewing pressure is adjusted on the pump body with a nut and bolt.

Unlike some internet lore, I assure you that the SCACE-II is required to actually measure and set the brew pressure on pretty much every machine out there. I did some experiments with my e61 which conclusively proved to me that was the case.

I did change the 0.8mm orifice (aka jet or gicleur) to a 0.6mm which is available from LM parts. There was a big thread on that subject some months ago. It does change the rate at which water flows out of the brew boiler, and has some side effects like slowing the rate at which pressure rises in the brew head. It has a side effect of altering the final pressure - which means you just have to re-calibrate with the SCACE to really know the brew pressure. Honestly, I don't think it made a lot of difference.

The LMLM is calibrated quite well at the factory, at least mine was. It produces very, very consistent temperature and pressure at the brew head. I've measured this enough times with the SCACE to be very confident in that.

All in all, it is a very good machine. It doesn't have lots of adjustable parameters for tweeking. It does what it is intended to do, stably and repeatably and produces very consistent coffee, shot after shot.

A G/S-3 MP, or a Slayer does offer more widgets to adjust. But a thing you can control often turns into a thing you must control. Pre-infusion can screw up a shot, just as much as it can make them better sometimes.

Amazing post. Thankyou. Brings back old un-answered questions for me about my lmlm and its preinfusion.

I had previously activated the brew lever and measured the weight of the tiny water trickle that came out prior to the pump coming on and it was like a teaspoon or similar. Since then i have ignored all mention of lmlm preinfusion as marketing hype and have considered it as a machine with no preinfusion.

Some thoughts since reading your post:

1. On your machine I would be fascinated to know the amount of preinfusion water that comes out with the brew pressure showing as 12 bar (primed) vs when the machine has been sitting for a while and brew pressure has dropped away. It seems like from your explanation there should be a noticeable difference in preinfusion water in the 2 scenarios.

2. I remember in an initial review of the lmlm that preinfusion was described as involving a coil shaped metallic tube that contained the preinfusion water? Is that in any way correct?

3. Sounds like you have used a scase with your machine. Do you know what pressure the 'preinfusion' water is? Are we saying its effectively a zero pressure trickle from the brew boiler or does it have a measureable pressure?

Fyi i just tried a few times in a row and measured the weight of the water drop until the moment the pump starts and it was a trickle that ranged between 3.4g and 4.6g which is around 1tsp hence my original thought of the machine as a machine without pre infusion. My brew pressure on the native dial peaks at 11.5 bar right after brew, and 14 mins later dropped to 4.5 bar, then climbed to 6 bar and started to drop again....

Actually, I've traced out and drawn a complete schematic of the water circuit, including all 4 check valves and the pre-heat, cold water bypass and everything.

That is a lot of work . . . thanks. I would like to receive a copy of your drawing(s) and/or sketches. My email is below my sig.

nuketopia wrote:Steam boiler pressure is adjusted to 1.3-bar on US models. The manual is translated from the Italian model and says 2.0 bar. You can adjust the pressure stat if you need it higher, but that seems a completely adequate pressure. I think it likely that all 120v models are adjusted to 1.3-bar at the factory.

Ah ok. No wonder! I have no complaints about mine reading 1.5 bar, I was just wondering why the discrepancy between the manual and my machine, but now I know!

nuketopia wrote:When the machine is idle, the brew pressure gauge should indicate 12-bar. There is a pressure relief valve just behind the drip tray that can be adjusted to maintain this pressure. It should be adjusted so that at idle, the pressure does not exceed 12-bar, but should be right at or just under that value.

I think mine is always just 9 bar, but I will have to double check in the morning when I make a drink again. That is good to know!

nuketopia wrote:When you activate the brew paddle, the first thing that happens is the brew solenoid valve opens, releasing pressure in the brew boiler to the brew head. You'll notice that the brew pressure gauge drops to 0-bar as soon as the valve opens. There is a 1-second delay before the pump is powered. This is the pre-infusion period, and you won't get good pre-infusion unless the brew boiler is idling at the correct pressure and the brew group has been recently used or primed (with a quick flush of water from activating the brew paddle).

Another great piece of info. I see why the idle pressure matters now. I'll have to check it the morning.

nuketopia wrote: A G/S-3 MP, or a Slayer does offer more widgets to adjust. But a thing you can control often turns into a thing you must control. Pre-infusion can screw up a shot, just as much as it can make them better sometimes.

I dont necessarily *want* control over pre-infusion, I just want SOME KIND of pre-infusion (even if it's just a fixed 5 seconds that I can't adjust), and I was feeling like the Linea Mini doesn't have any.

nuketopia wrote:The pump in the LMLM (as would be true in the Slayer or any other commercial/prosumer rotary pump) has enough volume capacity that you can't estimate your grind by the gauge at all, as you might have done on the Breville with its low-volume pump.

The preferred way to gauge your grind setting is by time and weight, especially on the pro machines.

Yea, that's what I've been doing. I use the VST 18 gram basket and I measure 19 grams in, then shoot for 38 grams out. It takes about 35 seconds according to my Acaia Lunar scale (I start the timer as soon as I flip the paddle).

Thanks again for the great info/post. I'll keep practicing and messing around with it to try to get the shots as good as I possibly can.

nuketopia wrote:When the machine is idle, the brew pressure gauge should indicate 12-bar.

Hey Nuke:

I checked my machine this morning after letting it heat up for an hour. My brew pressure gauge fluctuated between 9 and 10 bar at idle.

After purging the brew head for a few seconds, the pressure rises back up to around 10 bar, but if it sits for a little while, it drops back down to 9 at idle.

Should I make an adjustment so that the pressure is closer to 12 bar at idle?

nuketopia wrote:Steam boiler pressure is adjusted to 1.3-bar on US models. The manual is translated from the Italian model and says 2.0 bar. You can adjust the pressure stat if you need it higher, but that seems a completely adequate pressure. I think it likely that all 120v models are adjusted to 1.3-bar at the factory. . .

When the machine is idle, the brew pressure gauge should indicate 12-bar. There is a pressure relief valve just behind the drip tray that can be adjusted to maintain this pressure. It should be adjusted so that at idle, the pressure does not exceed 12-bar, but should be right at or just under that value. You can adjust it easily with a wrench (17mm as I recall) or even with your fingers if it isn't hot. Adjust, flush water with the brew padle for a second or so, then watch the pressure after you turn off the brew paddle. It should quickly rise and settle at 12-bar. It should hold this pressure for a considerable amount of time, like 30-minutes or longer. (if it doesn't hold the adjusted pressure for long, then a check valve or something is leaking and you should contact LM for service - they were quite helpful when I had a check valve go bad and the indicated pressure would drop in a short time idling).

The Quick Start Guide that came with my Linea Mini says that the steam boiler gauge "will read between 1.3 and 2.0 when ready to steam." Mine cycles between 1.7 and 1.9 bars.

The same guide says that the brew boiler gauge "should never read above 12 bars of pressure," but I do not see a minimum. Mine runs about 9.0 or slightly higher while brewing, and then goes to 12.0 immediately after I move the paddle to the off position. I tried letting it idle a couple of times to see what would happen to the pressure. One time it fell to 7.0 after 30 minutes, and the next time it fell to 9.0.

Rocky