Long Lauter time

[Mathias]

Hey everyone, i have searched the forum and found a lot of good information, on some of my problems. I brew on a 40 hl brew system with wet mill, mashtun with mixer, lautertun with rakes(2,3m), kettle/whirlpool. I frequently have problems with very long lautering time of 5-6hours, with 500-1000kg malt load. There is a long dics chain system drawing in the malt, where i can see alot of fin particles, which i suspect is clogging/blinding the lautertun grainbed and creating a stuck mash?

[Amit]

Are you milling too fine because you have a wet mill and you can retain the husks? Also how long do you Vorlauf ?

[dick murton]

Sorry, but I don't understand this part of the comment "There is a long dics chain system drawing in the malt....." Please would you explain in a bit more detail.

A couple of thoughts about the proccess.

Due to their size, large wet mills (for say 5 metre plus diameter lauters) soak the malt for some time before actually milling - I'm afraid I don't know how long a typical pre-soak time is, but somewhere else on this site someone talks about 10 to 30 minutes, and I would suspect normally is closer to the 30 minutes in big breweries at least., so, the first question is, are you pre-soaking for long enough prior to milling?

Secondly, what is your mill gap? I understand wet mill roller gaps are typically set at about 0.3 mm - certainly this is the setting used in a couple of jumbo breweries I have worked in briefly.

Thirdly, you are milling into a mash mixing vessel. Do you run the agitator continuously, and if so, what is the velocity of the rotor blade tips? Ideally, you would only run the agitator during mashing in, during heating phases if used, and just prior to mash transfer, to make sure it is evenly dispersed.

If using a mash mixer - what sort of pump are you using to transfer the mash from the mixer to the lauter? You must not use a conventional high speed centrifugal pump as this will macerate the grist badly - I have seen this in a couple of breweries. The pump needs to be a low speed, low shear, open impeller design.

Lauter tun. In theory you should only need about 8 rake blades, but in practice, virtually every small lauter I have seen is hugely under-raked. I would expect to see more than double this number. BUT, to run this number of rakes, the speed has to be very low otherwise you are likely to push the bed around with the rakes, rather than cutting through the bed. You should only need to run the rakes during mashing in / transfer from mash mixer and later in the runoff - though I know lots of people will have different opinions based on their experience. You need to work out what works best for you, but, I suggest, starting from minimal raking rather than continuous raking.

Assuming there is a grains discharge arm, is this arm immersed in the grain bed - again, I have seen examples, both in large and small breweries. This will rotate and destroy the bed structure.

My suspicion is that you are milling too finely though.

[MikeyB]

Long chain and DISC system....

[dick murton]

Ah. I had a feeling this wouldn't clarify things much. Any chance of a photo as I'm afraid this really hasn't help me visualise this and understand what it does, and why you think it might be affecting things. Thanks

[Mathias]

- Amit
Thank you for your reply. The mill gap is set to 1,4mm, so I don’t think I mill too fine. The vorlauf takes about 20min, with a flow rate of 8hl/h and a volume of 2-3hl.

- Dick Murton
Thank you for your reply. You’ve given me a lot to think about and further look into.
I’ll try to explain. The disc chain conveyor system transports the malt from a silo outside, through a tube with a chain running inside with disc attached in 20cm intervals.

Maybe it is different at our facility. The wet mill has a small chamber on top of it, where the malt gets presoaked for 1,5 min before getting milled. The malt does not get presoaked all at once.
The mill gap is set to 1,4mm, so maybe the problem could be that it is set too coarse. But do you think, that could make the lauter slow? Would it not mainly effect the efficiency?

I am milling into a mash tun, with a mixer in the bottom running throughout the entire mashing process. In regards to the velocity of the rotor blade tips, I don’t know. But I think the speed of the mixer is about 30 rpm.
I don’t know the type of the pump, I will definitely look into that. In my experience it takes 5-10min at 1450rpm to pump the mash over to the lauter tun. The looks of the process have troubled me. The transfer of the mash looks aggressive and not very gentle.

I have been running the rakes at different speeds, 4-50rpm, however I experience that no matter the speed, at some point of the lautering, the rakes starts to push the grain bed. Could you give an estimate of how slow you would rake? Do you go even slower than 4rpm?
The grains discharge arm is in a locked position during lautering, and do not disturb the grain bed. So I don’t think that is the problem.
Do you still think that the main problem is that we mill too finely, when the mill is set to 1,4 mm? Again, thank you for your reflections. My own main suspicion is that the transport is wrecking the malt and creating a lot of fine particles.

[dick murton]

Chain and disc conveyor system – no problem, I understand the system fully now. I wouldn’t have thought that would be causing a major problem as whilst this is not the most common system in use, it is considered quite acceptable, especially for whole malt – so ignore that for now.
Various industry sources quote (not my survey – an earlier employer) a mill gap setting of the FIRST set of rollers for water conditioned malt of 1.4 to 1,7 mm in a six roll “dry” mill (3 sets of rollers with separating sieves in case you are not familiar – look up Buhler for details if interested). However, a survey of a number of breweries showed they were more typically 1.7 to 1.9 mm. Because you are only steeping for 1.5 minutes before milling, you are not really wet milling, but highly conditioning, i.e. you are only really soaking the husk, and not soaking all the way through the endosperm, which is what true wet milling does (20 to 30 minutes soak time). So I think you quite possibly have the mill set too fine and are therefore producing too much flour. I would try increasing to 1.6 or even 1.7 mm, though I think the latter might be too coarse and will result in excessive loss of extract. Or you put in a much bigger steep vessel to give say 20 minutes steep time, and then you should be able to set the gaps a bit closer.
Without knowing the diameter of your mash conversion vessel, it is not possible to say whether the mixer speed is OK. However, if your mash mixer diameter is also 2.3 metres, at 30 rpm, your mash mixer blade is running at about the design speed recommended by some manufacturers, probably just a tiny bit fast, but not enough to worry about. However, as the MCV is probably somewhat smaller diameter, the blade tip speed should be fine at that speed.
Mash transfer – I assume 1000 kg mash takes about 10 minutes, and the 500 kg mash about half that. Assuming about 3 litres / kg, this would give a volume of 50 to 55 hl for 1000kg, which means you should have 80 mm transfer pipework with a single inlet into the LT for a mash inlet speed of approx. 1.5 metres / second. If the pipework is smaller than this then even with a correct design of pump, it will be damaging the grist to some extent. Unfortunately I can’t find a drawing of the mash transfer pump, but the general guidelines are “wide-throated slow-speed (below 1,000rpm) pump designed to handle solids in suspension with an impeller designed to reduce shear.” So I suspect that the mash transfer pump is doing some damage to the grist.
The lauter tun raking is currently almost certainly too fast. You don’t say how many rakes you have, but would expect a minimum of 12, possibly as many as 20 rakes in total, so you have 40 to 50 mm between the rake tracks. I suspect you have fewer than 12. Raking speed - fast enough to cut bed in acceptable time, but slow enough to cut bed, and not move it, one supplier quotes “Equivalent to 12.5 rakes / m2 / hr”, but that assumes their standard of 3.5 / m2.
You shouldn’t need to rake continuously, though see previous comments.
Sparge – never let the bed dry out until you have sparged with sufficient water to obtain the required volume and gravity in kettle, with the proviso of not allowing the gravity to drop below 4 SG / 1 P. You should not have a long slow gravity tail off.

[Mathias]

Thank you again for the reply

I think you are right about the conveyor system, not being the problem. I have tested the malt from silo and special malt in bags, loaded in a bulk hopper, which run through the same conveyor system. There where almost no small particles vs the silo malt, so I have ruled out the conveyor system.
I will be looking further into the mill setting and the recommended setting and if it is a “true” wet mill.
Yes the diameter of the MCV is smaller than the lauter tun. The mash pump looks to be a normal centrifugal pump. I will look into mash transfer pipe and transfer time, to calculate a mash transfer flow and maybe change the pump rpm setting. Cloud you recommend a flow speed for the mash transfer?
Sorry, i have misread the lauter tun speed, it is not RPM nut RPH rounds per hour. The lauter tun have 8 rakes which split into two small rakes in the end. Would it be correct to assume, if the lauter tun is 4m2, with 2 rakes /m2, that the raking speed should be 6,25 RPH, to reach 12,5 rakes/m2/hour?
This have given me a lot of insight and things to reconsider. But I think that our problem might be the malt supplier and the quality of the malt or the delivery process to the silo.

[dick murton]

If it is a "normal" centrifugal pump with the impeller design as per attached Centrigugal (!!) pump impeller (whether enclosed or open impeller), then this is the first thing to change as it will completely destroy the large particles. The, admittedly large breweries I have worked in have used the open box type - perhaps more clearly shown in the picture of the red one (open box mash transfer impeller 2). You may be able to use a mono pump. I haven't used one for this duty but others claim it doesn't damage the mash. Until you get the pump changed I wouldn't bother thinking about changing anything else. I do consider you have far too rakes to be effective at raking the lauter tun bed effectively, but put that to one side until the pump has been changed. Inlet flow rate into the lauter must be no more than 1.5 metres / second - about 50 hl / hr through 75 or 80mm ID pipe. No idea where to get a suitable impeller from, so suggest trying one of your local pump suppliers, or talk direct to someone like Kaspar Schulz or Braukon.

[beerme]

You might want to look at your vorlauf flowrate and differential pressures across the false bottom. When we started up our new brewhouse, we ran the vorlauf too quickly, got a beautiful bright runoff which was almost impossible to lauter. I also found that if I open the underlet rinse jets while vorlaufing, it helps clear out the fines, and reduces the bed compaction.

If you run a slow flowrate for the underlet and the first worts which are more viscous, you can increase the runoff rate with subsequent sparges. It may be counter intuitive, but running slowly at first allows you to establish a nice bed, and allows you to go faster without getting clogged up.

Our raking system is not ideal, and tends to help compact the bed. I run it while the lauter tun is filling, to distribute the mash, then stop when full, and allow it to rest 2-5 min before starting vorlauf. I like to run down the first worts until the liquid level is at or just below the surface of the grain bed. Then I stop the runoff, add sparge water and run rakes to lift and refloat the bed. It is important to stop run off while refloating or it will compact the bed. I then typically stop the rakes a few minutes before i start the runoff again, and flysparge: ie. add sparge water to maintain the bed level as i run off. I monitor differential pressures above and below the false bottom and can ramp up the flowrate as the lauter progresses.

I can run off 30 HL in 90 minutes including vorlauf and rests.


Issues you can research are: bed porosity, Oberteig

[Mathias]

Thanks for all the replies.

During the last couple of weeks, I have been looking into all the details and specs about the brew house system and implementing a lot of new practices. I have been using the rakes a lot less and at a lower speed, which has helped. But if I run the rakes for to long, even at a slow speed 2-6RPH, they start pushing the grain bed. The biggest problem to the long lautering seems to be the grain quality, which have gotten better, with less small grain particles. This have increased the lautering speed, and we have been able to lauter without any stuckmash or deepcuts.
-Beerme
Could you describe a little about your brewhouse system and lautering process?