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Thread: Vacuum in mash tun

  1. #1
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    Nov 2013
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    Vacuum in mash tun

    We’ve been experiencing a strange vacuum in our mash runoff, pretty independent of the grist. Looking to the tribe for some problem solving thoughts.

    Below are the details, but what we’re mostly seeing is the grain bed drop 10” almost immediately, even with a very slow vorlauf and sparge. When it starts to slow down, we see big air bubbles go back up the hose, through the sight glass and back into the mashtun. Sometimes the run off goes completely dry, but the mash still has an enormous amount of water in it. When this has happened and we finally call it, if we start graining out and shove a shovel into the grain bed, you can hear the vacuum break up.

    Mash tun: homemade 7bbl, we push 10bbl batches out of it. Dimensions are usually wider than taller aside from when we really max it out. This vacuum issue is common no matter what the volume is at.
    Batches: for any batch that uses flaked grain, we use rice hulls. Generally put some in at the beginning along with a good base of 2-row, then mix in more rice hulls with the flaked grains and the rest of the 2-row or other base malts.
    Temps: mash usually 150-153 for the majority of our batches. Its single infusion so sometimes it does dip lower like 145. Sparging with 170F water.
    Mash pH: 5.2-5.4
    Sparge: fly sparge, try to hold 1-2” above grain bed, but with this issue the grain bed drops several inches. Gravity run off into keggle grant, then pump into kettle, generally 5-10 minutes per grant. When this problem starts, it will go up to half hour grants.

    I drilled more holes into the false bottom and that didn’t make any difference.

    So... any thoughts would be appreciated as we are at our wits end about this.

    Cheers,
    Brian

  2. #2
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    Are you flooding the plates so you fill all the runoff pipes and under the plates with water? You should have about 1 cm / half inch of water above the plates before you transfer the mash, or start to add malt and mash water. Use hot water to pre-heat the MT for this?
    dick

  3. #3
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    Details....

    Quote Originally Posted by mook View Post
    We’ve been experiencing a strange vacuum in our mash runoff, pretty independent of the grist. Looking to the tribe for some problem solving thoughts.

    Below are the details, but what we’re mostly seeing is the grain bed drop 10” almost immediately, even with a very slow vorlauf and sparge. When it starts to slow down, we see big air bubbles go back up the hose, through the sight glass and back into the mashtun. Sometimes the run off goes completely dry, but the mash still has an enormous amount of water in it. When this has happened and we finally call it, if we start graining out and shove a shovel into the grain bed, you can hear the vacuum break up.

    Mash tun: homemade 7bbl, we push 10bbl batches out of it. Dimensions are usually wider than taller aside from when we really max it out. This vacuum issue is common no matter what the volume is at.
    Batches: for any batch that uses flaked grain, we use rice hulls. Generally put some in at the beginning along with a good base of 2-row, then mix in more rice hulls with the flaked grains and the rest of the 2-row or other base malts.
    Temps: mash usually 150-153 for the majority of our batches. Its single infusion so sometimes it does dip lower like 145. Sparging with 170F water.
    Mash pH: 5.2-5.4
    Sparge: fly sparge, try to hold 1-2” above grain bed, but with this issue the grain bed drops several inches. Gravity run off into keggle grant, then pump into kettle, generally 5-10 minutes per grant. When this problem starts, it will go up to half hour grants.

    I drilled more holes into the false bottom and that didn’t make any difference.

    So... any thoughts would be appreciated as we are at our wits end about this.

    Cheers,
    Brian
    I am going to need you to explain how you think you are getting a " vacuum " effect if you are gravity flowing into a grant. The pump suction should not be able to influence the grant, as its supposed to be at atmospheric pressure. Some things here do not add up. Your system may have some configuration errors that need to be looked at in detail based on what you are saying.
    Warren Turner
    Industrial Engineering Technician
    HVACR-Electrical Systems Specialist
    Moab Brewery
    " No Cell Phone Zone."

  4. #4
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    Quote Originally Posted by dick murton View Post
    Are you flooding the plates so you fill all the runoff pipes and under the plates with water? You should have about 1 cm / half inch of water above the plates before you transfer the mash, or start to add malt and mash water. Use hot water to pre-heat the MT for this?
    We collect about 100 gallons of strike water which is around 16-19” above the false bottom, and plenty below.

    We usually preheat by spraying down the walls for a few minutes, and while we’re collecting we keep the lids down. We measure the temp right before we add thw grain. Typically 170F strike water.

  5. #5
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    Nov 2009
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    Moab, Utah
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    Runoff

    Quote Originally Posted by mook View Post
    We collect about 100 gallons of strike water which is around 16-19” above the false bottom, and plenty below.

    We usually preheat by spraying down the walls for a few minutes, and while we’re collecting we keep the lids down. We measure the temp right before we add thw grain. Typically 170F strike water.
    How much time to go to kettle?
    I would suspect that your runoff rate is too fast among other factors.
    Warren Turner
    Industrial Engineering Technician
    HVACR-Electrical Systems Specialist
    Moab Brewery
    " No Cell Phone Zone."

  6. #6
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    Quote Originally Posted by Starcat View Post
    I am going to need you to explain how you think you are getting a " vacuum " effect if you are gravity flowing into a grant. The pump suction should not be able to influence the grant, as its supposed to be at atmospheric pressure. Some things here do not add up. Your system may have some configuration errors that need to be looked at in detail based on what you are saying.
    Quote Originally Posted by Starcat View Post
    How much time to go to kettle?
    I would suspect that your runoff rate is too fast among other factors.
    Runoff is between 1-1/2 to 2 hours. I would be shocked if thats the problem.

    To answer your other question... we know there is a vacuum because we see giant air bubble going back up into the mash tun. The runoff never completely stops, but the mash tun is gulping air from the grant, and even yesterday I completely removed the whole valve so it was just an open pipe and it was gulping air back up into the mash tun.

  7. #7
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    Apr 2017
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    San Antonio
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    The physics of this don't make any sense. Is the top of the MT fully sealed so as wort drains in to the grant nothing is displaced into the headspace? That is the only way I can see it drawing air into the outlet.

  8. #8
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    May 2012
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    Livermore, CA
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    661
    You have a stuck mash. Probably need to make adjustments to your mill to dial in the correct grind. Get a set of sieve pans and start opening up the gap .001"-.005" at a time to test between batches. What is happening is the outflow from your mash tun exceeds the rate that wort can filter through your mash bed. So it collapses to the bottom and then you're sucking air through a differential pressure gauge, or some pipe that is open to atmosphere and is below the false bottom. In the mean time, you can really slow down the flow out from your mash tun so that the grain bed does not sink.

    The other issue, if you are sure your grind is good, is going to be the pipe layout that connects your grant to your MT. I would make sure that you have a sort of P trap before the pipes dump into the grant or make sure that your pump never draws the wort below the top of the inlet pipe from the MT. you are getting air backflowing to the highest point, which is in your mash tun. Make sure there is a high point somewhere else in line before your MT or that the inflow pipe never sees air. You will otherwise let air flow back as the pipe drains.

  9. #9
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    Apr 2017
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    New Orleans, LA, USA
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    Hi, Brian. I'm looking solely at your mash tun.

    You said your tun is homemade and sized for 7 BBL, yet you are putting 10 BBL worth of malt into it. It sounds to me like your bed pressure (the weight of the mash itself) is too high and causing the bed to collapse immediately. This is exacerbated by a quick flow rate (you must be pulling most of the liquid really fast, really early on) which compresses the bed and can lead to channeling, among other things. I'm certain your mash efficiencies are low - we design our equipment to achieve 90% mash efficiency. How much malt are you using (how many pounds) and what are you yielding (how many kegs do you get)?

    Slow down your flow at the beginning and speed up as you get further along (still aiming for a 90-120 minute runoff).

    Have you tried a 5 BBL batch in this tun? How does that compare to what happens in a 10 BBL batch?

    If you want to consider new equipment, let me know. Craft Kettle designs and manufactures brewing equipment; a properly sized and engineered tun will solve your vacuum problem.

  10. #10
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    Quote Originally Posted by jebzter View Post
    You have a stuck mash. Probably need to make adjustments to your mill to dial in the correct grind. Get a set of sieve pans and start opening up the gap .001"-.005" at a time to test between batches. What is happening is the outflow from your mash tun exceeds the rate that wort can filter through your mash bed. So it collapses to the bottom and then you're sucking air through a differential pressure gauge, or some pipe that is open to atmosphere and is below the false bottom. In the mean time, you can really slow down the flow out from your mash tun so that the grain bed does not sink.

    The other issue, if you are sure your grind is good, is going to be the pipe layout that connects your grant to your MT. I would make sure that you have a sort of P trap before the pipes dump into the grant or make sure that your pump never draws the wort below the top of the inlet pipe from the MT. you are getting air backflowing to the highest point, which is in your mash tun. Make sure there is a high point somewhere else in line before your MT or that the inflow pipe never sees air. You will otherwise let air flow back as the pipe drains.
    I think this makes the most sense of whats going on - we try to lay a nice bed of 2-row and rice hulls first, and then mix in flaked grain, rice hulls, and more barley (2-row and specialities). I brewed this morning and I took the vorlouf runoff as slowly as possible, shut off the grant valve coming from the mash tun between grants when pump was in use, and the grain bed still dropped 10”. Whole mash started at 43” after dough in, by the 3rd grant (over the course of 40 minutes) the grain level was at 30”, but I was still collecting slowly and the gravity was good so I kept going. When I was 100 gallons in, the runoff dropped to a craw with all valves completely open. We are 7.5 hours in and finally called it at 265 gallons. We’ve tried all sorts of troubleshooting ideas but we’re no better off.

    I am wondering if we either need to add more rice hulls or mix in a different order. Basic grain bill for today:
    600 2-row
    260 flaked oats
    35 acidulated
    20 crystal
    25 rice hulls

    I will try to post some pics. I just grained out and there was stratification, definitely mashed potatoes with the oats, and the grain was still holding tons of saturation. The bottom was very compacted. Hardly any grain got through the plates, so its not a blockage issue.

    We do have a new MT ton ordered but we have to deal with this for another couple of month, so any additional thoughts are appreciated, as are all of the discussion happening so already.

    Cheers

  11. #11
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    Nov 2013
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    Winooski VT
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    Here is a folder of pics and vids from today. I would just try to go in order of the image number. Hopefully that will make sense. Let me know if you have any questions. Please do not share the link without asking.

    https://drive.google.com/open?id=1Ss...Mi914I4WqlPTaJ

    Thanks

  12. #12
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    May 2012
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    At those ratios, You could proably do just fine with no hulls. Ive run to 45% oats, wheat or rye flakes and no drop in run off speed. Above that, I just use 50# of rice hulls per 10 bbl batch. You can try more hulls if you want. What is that vertical hose coming from the tee after the sight glass? That is an air inlet potential, and your video with the air bubbles going back tells me that you are going to vapor lock under your false bottom from the air coming in. To fix that, you will have to scrape the false bottom with rakes or your mash paddle and then re-vorlauf. I would say get rid of that hose and go straight to the grant. see if you get the same problems then. I still suggest you may need to adjust your mill settings too. Also, your total be depth looks like it is pretty thick. You will loose tons of efficiency with bed depths much over 16"-20". We run them thicker when we have to, but vorlauf is much slower and efficiency is lower.

  13. #13
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    Quote Originally Posted by jebzter View Post
    At those ratios, You could proably do just fine with no hulls. Ive run to 45% oats, wheat or rye flakes and no drop in run off speed. Above that, I just use 50# of rice hulls per 10 bbl batch. You can try more hulls if you want. What is that vertical hose coming from the tee after the sight glass? That is an air inlet potential, and your video with the air bubbles going back tells me that you are going to vapor lock under your false bottom from the air coming in. To fix that, you will have to scrape the false bottom with rakes or your mash paddle and then re-vorlauf. I would say get rid of that hose and go straight to the grant. see if you get the same problems then. I still suggest you may need to adjust your mill settings too. Also, your total be depth looks like it is pretty thick. You will loose tons of efficiency with bed depths much over 16"-20". We run them thicker when we have to, but vorlauf is much slower and efficiency is lower.
    Ok thank you. That hose was an addition today. We ended up taking it out. It did provide some insight, but didn't help with the problem.

    We've tried loosening up the grain bed with the paddle all the way to the bottom, but again that did not seem to help.

    We get our grain pre-milled from BSG so we don't have control over the mill settings unfortunately.

    Bed depth makes sense... we've cut today's batch in half to do 2 mashes and it ran off even worse then the full batch. I can't explain it.

  14. #14
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    Problem #1: you have someone else mill your grain. I dont want to knock our suppliers, they do a good job of having the things we need. They are not brewers, and they do not know anything about your equipment. I know country malt will run sieve tests and dial their mill settings for you and are supposed to use those each time. I don't know what BSG policy on that is. Bottom line, I dont recommend any brewery open without full control of the process, including milling. They are probably one of the least expensive pieces to get. So I would say you should get a mill sooner than later and take over that part of the process. In the meantime, up your usage of rice hulls.

  15. #15
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    Quote Originally Posted by jebzter View Post
    Problem #1: you have someone else mill your grain. I dont want to knock our suppliers, they do a good job of having the things we need. They are not brewers, and they do not know anything about your equipment. I know country malt will run sieve tests and dial their mill settings for you and are supposed to use those each time. I don't know what BSG policy on that is. Bottom line, I dont recommend any brewery open without full control of the process, including milling. They are probably one of the least expensive pieces to get. So I would say you should get a mill sooner than later and take over that part of the process. In the meantime, up your usage of rice hulls.
    We just don’t have the ability to do that right now. Electrical inspector insists we need a separate room, and trying to cram that into our small space is impossible. Plus, any time its an all-barley grain bill, we don’t have this problem at all.

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