Unable to get clarity out of the MLT

[matarrayos]

Hi all!

I'm new to the forum and also to professional brewing, sorry for the long post. I work in a small brewpub in The Netherlands and we are having some problems with our brewhouse. It is a cute, Chinese manufactured, three vessel system: MLT, BK and HLT the three of them steam-jacketed and the three of them 7HL.



Our problem with clarity

We've brewed ten times with the system so far and we never get clear wort out of the mash-lauter tun; the liquid going through the sightglass is always murky and with quite a lot of grain chunks. The brewhouse is designed to recirculate with a pump through a manifold with no grant. We tried vorlaufing for up to 25 minutes with almost no improvement. We also tried simulating a grant by slowly draining by gravity into buckets and dumping them back on top of the mash for 15 min or so without any improvement neither.



--> Link to a GIF of our sightglass (I couldn't find how to embed an animated GIF here)

A couple of times we achieved good clarity but not for the whole lauter volume. It was shortly after starting sparging, when the first 150L were already transferred by gravity to the boil kettle and only 3 or 5 cm of wort remained on top of the grain bed. We managed to maintain those 3cm until the sparge water ran out, but the clarity started to get less good as we approached our target pre-boil volume.

Our problem with efficiency

Mash efficiency has not been very good either:

• Our best batch was 83% for a pre-boil gravity of 1.042
• The worst one was 70% for a pre-boil gravity of 1.065

Water to grain ratio was the same for both: 2.5 L/Kg over the false floor, with 30L under it.
But we also tried ratios as low as 2.2 L/Kg for 1.060 and as high as 2.8 L/Kg for 1.046 and efficiency was 74.5% for both.

We drain by gravity to the boil kettle until 300L have been transfer and then switch to a pump; by then the wort has been diluted and we never had an stuck lauter. Lauter time varies from 75 to 120 minutes with no clear relation to efficiency.

Our milling is coarse with 75% of the grains (by weight) remaining on top of a #14 sieve but no uncracked kernels; we use a two roll miller.

We treat our water with phosphoric acid and the mash pH at room temperature is close to 5.4. Calcium levels are at least 50ppm.

Generally we get better efficiency with lower gravity worts.

Additional data

We suspect the mash tun dimensions can have something to do with the efficiency problems. The inner diameter is 98.5cm so the average mash is easily 70cm tall and sometimes as tall as 90cm which does not seem like a good idea.



As you see in the pictures we have some rudimentary rakes which we use during mash in and we think make a nice job at avoiding dough-balls, we very rarely find them when we clean it. Besides that we don't use them at all; we know some people use them during sparge but ours are very close to the false bottom (2cm) and cannot be moved up and down. Also after the mash has settled the motor is not powerful enough to move again so if we want to move them we need to stir the mash a lot with the paddle to make it "float" again.



After the last brew session we found grain and "protein clumps" (not sure if that's the term) under the false floor, you can see them in the picture. We saw a thread here talking about using a short pipe to stop this matter from getting sucked by the pump but haven't tried it yet.

Any ideas that could help us? Thanks in advance!

[mmussen]

There's a lot of different possibilities as to why its not coming out clear.

I would think that the shape of the mash may have something to do with your efficiency, but I think you should also try adjusting your mill gap a little bit in either direction and see how that helps.
For the hazy wort I would suggest that you only run the rakes on the mash while you're graining in. Stop it as soon as all the grain is in an wet. If you let those rakes keep running you won't be able to set a filter bed and get clean wort. You might try mashing in by hand once or twice as well, just to see how that behaves. On the size system you have you really don't need rakes in there at all.
I'm not sure how much volume you're moving when you vorlauf but I would suggest making sure that its the total volume of water that went into the tun - you should be seeing some clarity by then.
You may also want to check your screens, and around where they sit to make sure there aren't any large gaps where grains could seep into the bottom.
Adding a small standpipe under the screens may help - but make sure that the tube in there is really in there - you don't want it deciding to move half way through the lauter, trust me.
Milling a little coarser may help clarity as well.

A final couple questions - have you calibrated all the thermometers, and has the haze cleared during fermentation and maturation? I only ask because the haze looks like it could be due to unconverted starch in the mash.

Good luck!

[matarrayos]

Hi Manuel, thanks for your reply.

It is a love-hate relationship with those damned rakes, we even thought about taking them apart, we may do it for the next batch, it is not difficult.

As for the coarseness of the grain I think we are at the limit, if we set the rollers gap a bit wider we start to see uncracked grains. Could it be that even with such a wide setting we are producing too much flour? It doesn't look like it though.

Regarding recirculation volume: how long should it take to recirculate 100% of the liquid? more than 25 minutes? We've read that more than 10 minutes of vourlauf starts to be counter-productive. Maybe we should try to set the pump a bit faster.

A final couple questions - have you calibrated all the thermometers, and has the haze cleared during fermentation and maturation? I only ask because the haze looks like it could be due to unconverted starch in the mash.

The MLT has only one temperature probe, 5cm over the false bottom; we calibrated it and it works fine when there's only water in the tun, but as soon as we dough-in we don't trust it anymore: it keeps showing the same value even 30 minutes after the grains are in. What we do now is this: we calculate the temperature we need the water to be so when it mixes with the grain we reach our target temperature (71ºC for a 66ºC rest) and it works pretty well. We check it with a hand digital thermometer in different places on top of the grain bed and also in the wort coming out of the recirculation pipe and it is where we want it to be.

We also do a starch conversion test (iodine) and it is successful. The clarity gets better after cold crashing but not crystal clear because we are not using any fining products.

[mmussen]

I usually vorlauf for 15 to 20 min. That's plenty of time for my system to get a nice clear wort. I do know a few brewers that vorlauf the entire length of the mash so I wouldn't worry to much.

I do usually get a few whole kernels when I mill with the gap at the setting I like. I'm not sure that would help as the amount on the screen sounds to be about right. I'm just trying to eliminate variables in as many places as possible.
Glad to hear conversion is successful, like I said, just trying to eliminate as many possibilities as I can.

I can't think of much else at the moment, but if something comes up I'll pass it on.

[Surfmase]

I recently brewed with a colleague who's LT rakes are not well designed. they are too flimsey and flex under load. Actually so much that they hit the bottom and pulled up a section of the false bottom. did you check how well your bottom is fitting?

[matarrayos]

I'm just trying to eliminate variables in as many places as possible.

I understand, that is also our approach. Thanks a lot, we have some things to try now.

I recently brewed with a colleague who's LT rakes are not well designed. they are too flimsey and flex under load. Actually so much that they hit the bottom and pulled up a section of the false bottom. did you check how well your bottom is fitting?

We have the suspicion that ours are not well designed either, but not in such a way. They are quite sturdy, I can't imagine something like that happening in our set-up. Regarding the fitting, I get inside the MLT to clean it after each brew (super-fun!) and I couldn't find any gap between the plates or the walls that is particularly big and can cause a problem.

What about the height and compactness of the grain and water mix?
After mashing in at 2,5 L/Kg the mix does not look very thick (but also not very thin) and after recirculating it compacts itself leaving around 30 cm of wort on top, because the MLT is so narrow and tall. Could that be too much? The couple of times we achieved clarity was after draining most of that liquid on top and maintaining only 3 - 5 cm of wort during fly-sparging.

[ipaguy]

I'd try using the rakes only during mash-in and at a very, very slow speed, paddle stirring also, but not too deep into the bed and only after there's a good base amount covering the screen. Stop the rakes as soon as all the grain is in and stir minimally and not very deep. Start the vorlauf at a very slow rate and very gradually start increasing the flow (e.g. run for 10 min. at x amount, then bump slightly higher for x amount, etc.). You'll have to find the max. rate you can run at and not have issues on your system.

[matarrayos]

Start the vorlauf at a very slow rate and very gradually start increasing the flow.

That is something we haven't done yet and could be interesting to try.
We always recirculate very slowly for fear or channeling but a bit more compactness may be better for filtering.
I will let you know if it works, thanks!

[dick murton]

That looks like a couple of systems I have seen from China. The first one, we threw out the rakes altogether (actually had to do it twice because the f..... Chinese installation "engineer" put them back in after we pulled them the first time). The system didn't need them at all because there was a mashing in device as well, which worked far better than I had expected.

Like your system, there are far too few rakes to use properly in a lauter tun. The speed of rotation was only suitable for use as a mixer (far too fast), but the rakes don't mix as they are not the right design for a mixer. So all in all they were a waste of metal.

The downside is, because you can't mix properly, or lauter with rakes properly, you can only really do isothermal mashes

SO...

Firstly, check the malt grind. Assuming you have a mill, then the setting should be fairly wide - sorry, I can't advise on a gap setting, as every mill is different. However, you shouldn't have much flour, mainly husk and coarse grits. If you can get a grist shaker, then you can set the mill reasonably well. Have a look at the following link - https://www.craftbrewersconference.c...ency-Havig.pdf

Secondly, if you have a mash mixer device - try throwing the rakes out. If you don't have a mash mixer, then once all the grist and water are in the MT, continue to mix for a couple of minutes more only to ensure the grist is wetted evenly, no dry areas only. Then stop the rakes and don't use them again for that brew.

Having done that, you should see the mash rise considerably as it floats due to entrained air. This is OK, it means you will have a porous bed for sparging. It is exactly what happens in a traditional British mash tun

If you have got the grind OK, with very little flour, but with every grain crushed open, you will only need a short vorlauf. anything more than a few minutes is more likely to compact the bed and give runoff problems. Also make sure the vorlauf is not too fast. Chances are that the transfer pump is oversized for wort runoff, undersized for effective CIP. So for example, if this is a 15 hl set up, consider taking 2.5 hours for runoff in total (don't worry, everyone will tell you something that works well for them and their kit, their malt grind etc. You can adjust after a couple of trial brews). So this means a flow rate of say 10 litres / minute. Vorlauf at say 15 litres for 5 minutes (and slow down once you start runoff to kettle). Basically you want enough, but not much more with a coarse grist, to transfer the very dilute wort at the bottom, to the top of the MT grain bed. Again, you can adjust this time and on subsequent brews. Trad British MTs, using ale malts often don't vorlauf at all - and we don't have problems with excessive flour - because the malt is coarse and floats rather than sitting on the bottom.

[SBCbrewer123]

What about the height and compactness of the grain and water mix?
After mashing in at 2,5 L/Kg the mix does not look very thick (but also not very thin)

Unless I screwed up my Metric conversions, I'd say your water/grain ratio is about right, so I don't think thats a likely cause.

after recirculating it compacts itself leaving around 30 cm of wort on top, because the MLT is so narrow and tall. Could that be too much?

Again, unless I screwed up my conversions, 30cm of wort on top of the grain bed after vorlauf does seem like maybe a little too much, but I've had more than that at the start of run off without problems

The couple of times we achieved clarity was after draining most of that liquid on top and maintaining only 3 - 5 cm of wort during fly-sparging.

Forgive me if I'm misunderstanding you, but are you starting your sparge right after vorlauf and when you start running to kettle? if so this is possibly the source of your problems, I've always slowly started running to kettle after vorlauf, and waiting until I can see the top of the grain bed. At this point I use a paddle to level out the top of the grain bed, then start my sparge and resume running to kettle. Throughout the runoff I will maintain ~10cm (I think) of sparge water over the grain bed (no wort is visible at this point). This does a few things. First, the more liquid on top of your grain bed the more weight there is to compact it. This can create uneven flow or cause liquid to blow through certain areas and not others, which in my experience leads to a lot of grain making its way into your runoff (and efficiency problems). This is especially true if your MLT is too tall/skinny and your grain bed is already pretty deep. Second, waiting until your first wort falls to the level of your grain bed allows your sparge water to "follow" your first wort, not only does this not dilute the wort that was already in your mash, you get better extraction of whats left on/in the grainbed. This might help address your efficiency problems. Sorry if this was a long winded response and I misunderstood what you said.

[matarrayos]

Have a look at the following link - https://www.craftbrewersconference.c...ency-Havig.pdf

Hi Dick, the link you posted is broken but I'm sure it is the Van Havig presentation on Mash Efficiency. It's funny that you mention that because we attended his lecture this January in the Dutch Craft Brewers Conference. That's the reason we bought the #14 sieve and did the test. For the rest of the people interested in it: Link to the presentation from the Dutch Conference website

Secondly, if you have a mash mixer device - try throwing the rakes out. If you don't have a mash mixer, then once all the grist and water are in the MT, continue to mix for a couple of minutes more only to ensure the grist is wetted evenly, no dry areas only. Then stop the rakes and don't use them again for that brew.

That's more or less what we are doing now, but we'll pay a bit more attention to stopping them as soon as possible.

Some questions regarding the rest of your reply:
I'm curious about the whole "floating mash" thing, I read about that in New Brewing Lager Beer by Gregory J. Noonan but it is not clear to me if that consistency should be maintained for the whole run-off and sparge or if after vorlauf and first minutes of draining the grains should start to compact and sink.

Our pre-boil target is about 7HL so using your figures for flow rate the total run-off time should be 70 minutes. After Van's talk we aim for 90; sometimes it has been 70, sometimes 120; we saw no big differences in clarity or efficiency there.

Forgive me if I'm misunderstanding you, but are you starting your sparge right after vorlauf and when you start running to kettle? if so this is possibly the source of your problems, I've always slowly started running to kettle after vorlauf, and waiting until I can see the top of the grain bed. At this point I use a paddle to level out the top of the grain bed, then start my sparge and resume running to kettle. Throughout the runoff I will maintain ~10cm (I think) of sparge water over the grain bed (no wort is visible at this point).

Our procedure is very similar to yours. We do wait until the wort on top of the grain is about 5 - 10 cm and start sparging without stopping the flow to the kettle; at the same time we level the grain bed with the paddle very carefully.

…the more liquid on top of your grain bed the more weight there is to compact it. This can create uneven flow or cause liquid to blow through certain areas and not others, which in my experience leads to a lot of grain making its way into your runoff (and efficiency problems). This is especially true if your MLT is too tall/skinny and your grain bed is already pretty deep.

This is one of our theories, specially because we keep seen a lot of pieces of grain throughout the whole sparge; somehow they must be sucked through the mash. Another theory is that the vorlauf flow is not strong enough to compact the bottom of the grain bed (and also clean the debris under the false floor). Could a faster vorlauf help us get the first runnings (before sparge) clearer? Or could that cause more compactness and uneven flow? And also: how can we know if the flow rate is too high or too low?

Thanks for your reply; even if you misunderstood some parts it is good to corroborate procedures to try to eliminate some factors.

[jebzter]

Another design element that is poor on your MT is the single port drawing wort from the MT. In most systems, you have multiple ports spaced out about 2/3 the diameter, plus one in the center. This makes sure you draw evenly from around the MT. In your case, I would suspect that the flow rates are slow as they should be, but sediment is sliding down the bottom to the center during your whole run off. Also the reason for your lower efficiency could be attributed to this. Less flow through the outer parts of the mash bed means you probably leave some sugars behind in those areas.

[SBCbrewer123]

how can we know if the flow rate is too high or too low?

in my experience either by the liquid level in an airless grant, or by timing GPM in a bucket grant/literal bucket. I've never used a MLT without a grant before, but I've seen some that were equipped with a sightglass that runs from underneath the false bottom and up the outside of the tank, so you can avoid pulling too fast and compacting the grain bed.

Another theory is that the vorlauf flow is not strong enough to compact the bottom of the grain bed (and also clean the debris under the false floor). [B]Could a faster vorlauf help us get the first runnings (before sparge) clearer?

I would be interested to know if anyone else has an answer for this, while my runoffs arent as cloudy as yours I do get a bit of particulate in the clear first wort (the vast majority of which settles out in my grant fortunately), and I vorlauf pretty gently.

[dick murton]

That Havig presentation is the same as the one I posted the link for.

For a 7 hl mash system, I have only every used a single central runoff point, best results for a single pipe being obtained when at the bottom of a shallow cone of say 5 degrees. Any more pipes than that for a tun this size means the pipes are even less likely to be cleaned effectively. Large lauter tuns, for example the ones at my last major brewery had one every m2 to 1.5 m2 approx., but they were 10 metre diameter, so needed a fair few. We also had horrible problems with cleaning the runoff pipes, even with a reasonable CIP system - due to low flows through each of these runoff pipes. I have a photo of a 3 inch collection pipe with what was probably a 1.5 inch or less hole left due to accumulation of crap around the perimeter, which had built up over a number of years. For a smaller system, one runoff every 1.5 to 2 m2 seems to work fine

The floating mash means that there is a load of air entrained in the mash, which maintains porosity of the bed so you don't need rakes. It does really need coarse grist to help trap the air, and no beating the daylights out of the mash with paddles / rakes etc.

[UpsidedownA]

Mill setting may be too coarse

It's possible for the mill settings to be too coarse. 75% staying on the #14 sieve seems very high. The German textbooks (even if they don't use the actual #14 etc numbering) have #14: 18-25%, #18: <10%, #30: 35%, #60: 21%, #100: 7%, pan: 11%. If the crush is too coarse, you could have ungelatinised bits of starch clinging to the husk. I suggest you do a starch test on your spent grains to see if there's any there. Do a starch test on your wort running off to see if there's any coming through. if the wort is too dark to see the reaction easily, dilute it with water and try.

Finer mill settings will help with your efficiency too.

Plenty of lauter tuns for pub breweries/microbreweries have fixed rakes and rakes with only two arms. There's a brewery in Dublin with a brand new Caspary brewhouse with fixed rakes. I believe the method they use is mash in the kettle etc, then underlet the lauter tun and transfer into the lauter tun, the mash settles onto the false bottom, they rest for three minutes, then recirc for 4 minutes, then recirc with the rakes on very slowly (e.g. one revolution in three minutes) for three minutes, then recirc without the rakes for 2 minutes, then recirc with the rakes again for 1 minute, then recirc without the rakes for 5 minutes. The raking during the recirc is to put smaller particles back onto the top of the bed, or something. Anyway, they have very clear wort at the end of that. They don't use the rakes again or only once or twice slowly for a single revolution during the whole run. lauter time 2hours.

The vessel diameter doesn't seem too bad to me. Given the diameter, it must have a surface area of about 0.76 m^2. 1 draw off point per square meter is pretty standard. A standard loading for a lauter tun is 150-160kg/m2 so you should be using 120kg malt per batch. That should give you 700litres of 1.044 wort at an efficiency of 85%, pretty much what you're getting.