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Thread: Lauter Tun Run off

  1. #1
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    Lauter Tun Run off

    Dear all,

    I try to better undestand the lautering process in order to optimize a lauter tun and reduce the lautering time in a 1ooHL brewery installation. I have some questions and I would really appreciate any help:
    - How does the false bottom "free surface area" affect the lautering process? As what really does the filtering is the bed, why not make the free surface area as high as possible?
    - What is the role of the regulating valve between the run offs and the grant? Why do we need to slow down the run off rate?
    - Can a freqency contolled pump directly be connected to the run offs? Or is it better to let gravity do the job and use a grant?
    - Is there an "optimum run off rate"? How can it be calculated?

    Thanks in advance,
    George

  2. #2
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    You want to draw off the mash slowly, which is the purpose of the lauter grant. If you pull wort from under the mash too quickly, you run the risk of compacting the mash, reducing or even minimizing spaces between grains for the wort to run off through. This is very likely to lead to a stuck mash. That is why you use the valve to regulate the flow. Gravity is best here.
    The correct runoff rate depends on the geometry of your lauter tun, but ~15 min per BBL is probably a pretty good ballpark for smaller systems.
    -Lyle C. Brown
    Brewer
    Camelot Brewing Co.

  3. #3
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    Ok, but if you have a grant and so you isolate the pump from the lauter tun run offs, you don't actually pull wort. You just let it flow with the gravity force. Do you still need to further reduce the flow by using a regulating valve?
    Can wort flow be controlled by just cutting the bed on the right time and depth?

    Isn't "~15 min per BBL" too slow???

    PS
    Please note that I am an engineer and not a brewer!

  4. #4
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    Hey George,

    One goal of lautering is to filter out haze-forming proteins and solid chunks. The proteins are small enough to flow through the false bottom, while the chunks flow through the gaps between the false bottom plates and the lauter tun shell. The grain husks will effectively seal the gaps and filter out the undesirables, but the grainbed needs to be set - i.e. compacted to a certain degree - first. To get the grainbed to set properly via wort recirculation, the minimum lautering load is probably around 199.5 kg of grain per m2 of false bottom area (that's the loading design of the Steinecker Pegasus lauter tun, which very few of us can afford). At 1.5 quarts per pound, a 199.5 kg/m2 load would result in a pre-lauter mash depth of around 30".

    For craft brewers, let's assume the typical pre-lauter mash depth is 36". Let's also assume, for the sake of illustrating a point, that a false bottom loading of 40 kg/m2 is possible. That would result in a pre-lauter mash depth of around 6". If we assume that the lauter tun is a closed cylinder with a height 1' greater than the pre-lauter mash depth, a wall thickness of 2" and a false bottom thickness of 1", and that the mash volume is 100 hL in both cases, the low-load example will take up about 6x the amount of floor space and require over 4x the volume of stainless as the standard-load example. That's a lot of cash, both in raw materials and facility rent. These problems are addressed by breweries that use mash filters instead of lauter tuns, but mash filters have other issues and are only used by a handful of mega-breweries (as far as I know).

    Running off the wort too quickly, whether by gravity or a pump, will over-compact the grain bed. You can monitor potential grainbed compaction by measuring the difference in pressure between the top and bottom of the grainbed. The bottom pressure needs to be lower for liquid to flow, but you want to keep the difference small to avoid over-compaction. If the grainbed is over-compacted, the pathways through the grain husks will close and the runoff will slow to a trickle. Cutting the grainbed helps keep things loose, but you don't want wort to only flow through the channels created by the lauter rakes. If that happens, you'll leave a lot of sugar behind with the rest of the grain that the wort isn't flowing through (and extract a lot of astringent polyphenols from the wort pathways).

    In terms of barrels per minute, each brewhouse is different. That's why beerking1 said "for smaller systems", and a 100-hL brewhouse is definitely not a small system for craft breweries. 15 min/bbl would be ridiculously fast for a 5-gallon homebrewery. A more universal measurement would be minutes per kg/m2 (or lb/ft2) of false bottom loading. My guess is that 1.25 min/(lb/ft2) is about as fast as most breweries can go without over-compacting the grainbed, and the initial flow due to gravity without flow restriction would be much faster than that.

    For what it's worth, I've worked in a brewery that gravity-feeds into a grant and another that pumps directly from the lauter tun. Both methods work fine as long as the runoff isn't too fast.

    Joe
    Last edited by jwalts; 03-12-2009 at 08:48 AM.

  5. #5
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    depends

    Quote Originally Posted by jwalts
    Hey George,

    To get the grainbed to set properly via wort recirculation, the minimum lautering load is probably around 199.5 kg of grain per m3 of false bottom area (that's the loading design of the Krones Pegasus lauter tun, which very few of us can afford).

    Joe
    200 kg/m2 is approaching the upper not lower limit on the systems I've worked on. Does of course depend on the milling gap and amount of mash in water as well.

  6. #6
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    Whoops, I meant m2 and ft2 instead of m3 and ft3 for loading rates. Sulfur, I'm interested in 200 kg/m2 being your maximum. I wouldn't think that mill gap and mash water volumes affected the dry grain loading. I based my numbers off of this website, which lists Boulevard Brewing as having a 230 kg/m2 load:

    http://www.krones.com/en/industries/670.htm

    The brewpub I used to work at had a dry lauter load of around 215 kg/m2 for a 12P wort. We would get as low as 170 kg/m2 for lower gravity worts, but that was rare and we'd go as high as 300 kg/m2 for high gravity worts. How low does your brewery typically go? The specific loading limit was a tangent to my original point (my fault for mentioning it) that lauter tuns need sufficiently-deep grainbeds for wort clarity and keeping equipment costs reasonable.

    Joe
    Last edited by jwalts; 03-13-2009 at 09:01 PM.

  7. #7
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    krones

    Well, the Pegasus is a very modern Lautertun and has the latest engineering behind it, so it's no surprise they can up the specific weight. They also probably condition their malt with water. Assuming all that, it's normal to go up to 250 kg/m2. But in a brewpub, and I've worked at 2 (using German equipment), then 200kg/m2 or so is towards the upper limit. Mill gap and mash volume are factors not in the specific weight, but in being able to lauter effectively.

  8. #8
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    Hi Joe,

    thank you for your comprehensive answer. Although lauter rakes cut grain bed during raking, I believe that the channels created, do "disappear" in a while, at least while wort level is above grainbed. And this is because grains are maintained in suspension.

    Could you also please explain what do you mean by "1.25 min/(lb/ft2)" or can you say what you think is the optimum flow rate for a lauter tun that has a 10.68m2 false bottom (12% free area) wth ~175Kg/m2 load.

    George

  9. #9
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    Hey George, all I meant was that the fastest runoffs I've seen take about 1.25 minutes for each lb/ft2 of false bottom loading. That depended on a false bottom load of 200 kg/m2, though. As Sulfur points out, that number probably isn't representative of typical breweries. For the sake of figuring out a runoff rate, let's redefine the number. A typical lauter, in my experience, is around 90 minutes. If the associated false bottom load is 155 kg/m2 (I just found a brochure on the Pegasus that says it operates at 1.3x the load of a classic lauter tun), the lauter rate would be 90/155 = 0.581 min/(kg/m2). Using those numbers, a normal runoff on your system would be [0.581 min/(kg/m2)] x [175 kg/m2] = 102 minutes. I've seen runoffs as fast as 45 minutes, but let's call 60 minutes the fastest you'll want to go. Not much point in going faster than your kettle's heating time. That would result in a maximum lauter rate to 60/155 = 0.387 min/(kg/m2). On your system, the minimum runoff time would be .387*175 = 68 minutes. The free area of your lauter tun doesn't matter once you've figured out your loading, and all bets are off when your mash includes grains that aren't malted barley.

    This type of analysis doesn't have much practical application, unless you plan on using a very unusual grain loading. All the brewers I know just learned from experience how quickly they can lauter on their brewhouses without over-compacting their grainbeds.

    I don't understand the fine details of lauter rake operation, but I can guarantee the grains won't be suspended if the bed is over-compacted by lautering too quickly. That's when channeling would occur.

    Joe
    Last edited by jwalts; 03-13-2009 at 06:21 AM.

  10. #10
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    German LB

    Sorry but I don't agree with the 90 minute typical time either. At least with a classical German (i.e. not a mash/lauter tun but a stand alone lauter tun), the typical times are more near 120-180 minutes (and that's for a normal 12P beer, an 18P would take more). That is total time including even the time it takes to fill the Lautertun (because for planning purposes if you've got another batch right behind the first one, what matters is the total time the vessel is in use.) The numbers with the Pegasus refer to this kind of setup and so shouldn't be compared with for example a mash/lauter vessel.

  11. #11
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    Man... I derailed this topic, but you sent it into an alternate universe. Yeah, setup and cleanup times will determine how many brews you can fit into a day. No, they don't have anything to do with what we were talking about (runoff rate). Ninety minute runoffs were standard for both of the breweries that I worked at, and one of those breweries had a four-vessel brewhouse with a dedicated lauter tun. If I add 10 minutes to fill, 10 to vorlauf, 20 to grain-out and 10 to rinse/add foundation water, it ends up being 140 minutes. Wow, we agree.

    Joe
    Last edited by jwalts; 03-13-2009 at 11:26 AM.

  12. #12
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    Hi Joe, well the discussion is on the topic of lautering, but I guess you're right. My apologies and it's good to see we're both excited by what we do! Cheers.

  13. #13
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    Dear all,

    thank you for your replies. Today I modified the raking mechanism of the lauter tun by placing much more rakes. The result is at least 30% shorter lautering time as the runoff flow is much higher now and the grainbed more even.

    The next step is to calibrate and utilize the pressure transmitters placed on the lauter so as to automatically adjust the regulating valve and/or the raking mechanism height. Any suggestions on differential pressure and what is considered as normal?

    George

  14. #14
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    What is happening in lautering is diffusion of sugar-heavy liquid into less-dense water. You should balance run-off rates versus efficiency and come up with something acceptable for your situation. If you could run off in 10 minutes, big whoop if you are leaving all of your extract behind in the lauter. A 20 minute longer runoff might be a percentage increase in efficiency, which will save you money in grain in the long term. Or if you are pressed for time, you might be willing to give up a percentage efficiency to turn around the lauter tun faster. It all depends.
    Linus Hall
    Yazoo Brewing
    Nashville, TN
    [url]www.yazoobrew.com[/url]

  15. #15
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    Interesting discussion. Oddly enough I am doing much the same at a rather larger brewery at present. However the principles remain pretty much the same. I haven't reviewed any of the figures quoted yet as I have only just logged on after a couple of weeks absence.

    The free surface area does make a difference. Basically the higher the surface area the faster the runoff possible - up to a point. The grist ratios are important. Complete husks, free of attached endosperm are ideal - retined by a 1.4 mm sieve - aim for 600 ml / 100 g. Then the minimum amount of flour - less than 10 %, and the rest as grits. But I am having trouble achieveing this with a six roll mill and conditioning, so trying to achieve it with a 2 roll mill.....

    However, if it is of any interest, if you look at the latest systems, they all appear to be operating on pretty much the same principles. The target is to run at a constant flow rate, using the rake speed & height as the main control. If these fail to control the runoff, then slow down the runoff rate until the diff recovers.

    Transfer the mash, and vorlauf - possibly by pulsed recirculation at high speed to clear the debris from under the plates. Run off the strong worts at the target flow rate so not to blind the bed, start sparging with just a small level of wort above the bed, then match the runoff and sparge. Simple. I wish. Of course, this requires decent automation. Another system, and because of LT loading, what I am using is to set a highish strong worts runoff rate, and once the sparge has started to progress through the bed, start increasing the flow rates. I don't know the rates / unit are off the top of my head I'm afraid - another day
    dick

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