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Thread: Vacuum in mash tun

  1. #16
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    Because this only happens when you are using oats and other flaked grains the issue may just be about poor mixing of your grist. It seamed in one of your photos that you had large clumps of oats, possibly even a layer. If your flakes are better distributed through out your bed it may help. Maybe try pre mixing dry flaked grains with rice hulls prior to mash in and give the whole mash a good stir once or twice during the rest.

  2. #17
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    Apr 2010
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    Massachusetts
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    Hi Mook:

    Looking at image 8376: your false bottom seems like it could use WAY more permeability.

    I know you are waiting on a new mash tun, but you might want to invest in a real "wedge wire" false bottom to use in the interim. I just did a quick google image search and there appears to be a few sources of pre-fab false bottoms. I bet you could easily retrofit one of those into your current tun for short(-ish) money until the new one arrives.* It looks from that photo that you have a radius on the bottom of your current tun, which will give you some wiggle room as far as sizing an off-the-shelf bottom.

    (* Or if your new tun is similar in size to your current one, see if the supplier of your new one will send you that bottom now. Again, I think that radius on the bottom of your tun will give you some flexibility with sizing.)

    As for the pre-milled grain, I doubt that is the issue in this case. We are a BSG customer and purchase pre-milled grain (27000+ #/month) from the RI warehouse which, I believe, is the same warehouse you get yours from in VT. We did, indeed, have milling issues in the past, but they acquired a new mill about a year ago and our crush has been spot-on since then. And yes, we check it with sieves on our end.

    Good luck and cheers- Mike

  3. #18
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    Oct 2002
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    I don't think you need a new mash tun false floor. I have used plates with far fewer holes than you have in those.
    What you do need is some air entrained in the mash. In a mash tun, the mash should float, and shortly after you have finished mashing in, you should see the mash bed rise above the original level. If floating effectively you will have about an inch of mash ABOVE the mash liquor.
    So, picking up on a couple of points previously made
    You say you 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). Looking at the bed, you have created a virtually impervious layer at the bottom of the bed. The malt grist doesn’t look particularly well milled, but because of the other stuff, it is difficult to be sure. You should have very large husk particles, with no endosperm attached, but every grain should be split open.
    DON’T layer the materials. This is the major cause of the impervious layer. Because you don’t say whether you have a grist case and mashing in device, or mash in by hand, this requires effectively two answers, with the same result.
    Assuming you have a grist case, add the bags of ingredients to the grist case so you get the same proportions – e.g. 1 x 50 pound bag of 2 row, followed by 25 pounds oats, followed by 3 pounds acidulated, followed by 2 pounds crystal and then 2 pounds rice hulls, then repeat this sequence
    If you don’t have a grist case and are stirring in by hand (I suspect you are not, but if you are, I wish you the best of luck with that!) then split everything up so you have say 18 x 50ish pound bags, each with an 18th of the quantity of each ingredient into each bag. Then stir in one bag at a time.
    Personally I would have thought that much oats would be excessive, but I bow to experience.
    Don’t worry about bed depth as such – but the deeper the bed, the slower you have to run off. I have worked with mash tun beds 5 foot deep, but admittedly, we took about six hours to run them off. So you may well need to run off much slower – perhaps as long as 4 hours. I suggest you aim for a 4 hour runoff with this bed depth, and if you getting good results, only then you can see if you can speed it up without blinding the bed. You may need to run off slower.
    Finally, I would remove that vertical tube after the sightglass. All you have done is create a bug trap. You don’t need it because you have an open underback. AND, I would lower the underback somewhat
    Let us know how you get on
    dick

  4. #19
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    Oct 2013
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    Here is my suggestions and explanation of the symptoms.

    You are layering the oats and thereby causing a compaction layer somewhat in the middle of your grist bed. You can see this in some of your images. Basically that hydrated layer of oats is creating a closed vessel situation. The draw off your are pulling to the grant creates a negative pressure differential in the mash bed causing further compaction, and solidifying this mid-bed lid-effect. You are able to draw enough wort until the DP is too high, causing the bubbles you see in the sight glass, and the vacuum effect. This is why liquid can be on top, but none underneath.

    It is not uncommon for your mash to rest and settle below the liquid level, so that is not of concern. How do you vorlauf? How long and how fast? When are you starting to sparge? Sometimes I will "float the bed" and actually start sparging very early at a significantly reduced rate. IE - run-off at 2.5 GPM while sparging at 1.25 GPM, until proper liquid level is reached. Then increase the sparge to match flow rate. This helps prevent bed compaction and minimizes efficiency loss in deeper beds. If you have lifting rakes, its not really a concern.

    Now suggestions previously mentioned are great, but mainly look at Pivo's suggestion of mixing the mash better. It should not be layered ever, and should be thoroughly mixed evenly. Rice hulls can help, but as Jeb says, I have done 40% wheat without hulls or enzymes, just using proper technique, and achieved a 90 min run-off with good efficiency. I also ran over 20" bed yesterday (system max), with very little efficiency drop.

    I would counter others remarks and suggest you leave the Tee & Tube (Manometer) but change the placement. Many, many systems are designed exactly like this without a grant at all. I use one currently. If you want this to help you out, move it before the run-off valve. The tube will then be a Manometer designed to show you the pressure differential in the grain bed. You would see it drop to the bottom and pull air during your problem runs. You should be running off at a speed that barely drops the manometer level below the mash liquor level. You should NEVER open the mash run-off valve fully or you will just blind the screens faster.

    All comments on grain mill, wedge-wire (by far the best), and rice hulls are agreed with, but not likely your source issue. Mix the mash better and slow your draw/vorlauf rate. Get a micro-adjustment TC valve if you need in order to get the proper run-off rate to your grant. Do not mess with the run-off rate too much during the lauter. If you cannot manage a reasonable run-off time without dropping the manometer level too far, then you need to adjust the false bottom (more holes), or reduce your mash loads.

    Just my $0.02 - Let us know if you get it sorted!

  5. #20
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    Re vorlauf rate - I have worked at several breweries with mash tuns that don't (cannot) vorlauf - traditionally British MTs didn't vorlauf, this is something that has started with, I suspect the US micro brewing fraternity, and nothing wrong with that, it definitely helps reduce the crap going into the kettle. So, you will need to vorlauf slowly, or do what many of the big lauter tun ops do, which is to have very short bursts at high flow rate. You could try simply not vorlaufing for a brew or two until you get a feel for the start of runoff flow rate.

    I agree that a better valve to control the flow into the underback is a good idea.

    "Move the sightglass tube before the run-off valve. The tube will then be a Manometer designed to show you the pressure differential in the grain bed." Yep - good point, this is probably far better than stripping out altogether - just make sure you clean the damned thing properly though.

    20 inch bed in 90 minutes is fine, but I think you have something like a 4 ft deep bed when mashed in, based on the pictures - so definitely try a four hour run off - sorry about that, but better slow and get it first time, and then speed up progressively during subsequent brews
    dick

  6. #21
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    Vorlauf is a German carry-over and roughly translates to "Before-Run". Many will tell you it is "recirculation", but that is a contextual interpretation. I am fairly certain there is equipment designed with this process in mind prior to American brewing altogether. I will have to crack the books to verify. In any event, Bamforth and others have successfully challenged the need for clear wort, but I vorlauf for a more important reason.

    Setting the grain bed is the best argument for vorlauf, IMHO. If done properly, you can run off consistently without variance in flow rates and achieve ideal extractions. Personally I would avoid high flow bursts, simply because it will increase compaction of the grain bed. As Dick says, I would simply run direct to kettle extremely slowly with incremental increases in flow rate. This would help "settle" the bed as opposed to compact it. The less the bed moves while pulling wort, the better in my experience. If you can cut the bed, then you can push a bit harder.

    My old British style pub system was not designed with the ability to recirculate, but I found it so valuable that I would run into buckets at a rate matching my desired run-off rate in order to simulate vorlauf. I would then pour the buckets carefully back into the mash. This would stabilize the bed so I didn't run into suck mashes. Very labor intensive, but then again, the only stuck mash I have faced was when I left the "help" in charge on a lunch break (different system). Longest lunch break I've ever taken. Plenty of slow mashes over the years, but nothing toping three hours. I know I've run up to 36" deep in those times as well. All those 35bbl or smaller though. Plenty with oats, rye, wheat, & flaked stuff. Now 4' is still a lot deeper than 3' to be quite sure.

    Manometer is a great tool for determining the acceptable run-off rate of your mash. No need for arbitrary run-off times. 90 mins ~ 20 in was my anecdotal example. Let the mash tell you how fast to run. You can watch for the differential levels in the manometer tube and the mash liquid level. Maintain a differential level of 1-2" at first to ensure you are not pulling too hard on the bed. Once you have collected a known volume, back calculate the total run-off time. If it is beyond acceptable, slowly open the mash valve and increase the differential level to 2-3" and re-calculate. Know that the larger your differential, the greater the risk of a stuck mash. It could very well take 4 hours based on your false bottom permeability. Permeability is something you can calculate based on surface area and hole size/number. I would not think this is the case if you are pulling vacuum. Float your sparge as suggested if you are super worried about compaction. Drop the level slowly.

    I like a pre and post manometer valve allowing me to isolate and pack with hot NaOH solution. Rinse until pH neutral. Clean as a whistle.

  7. #22
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    Re vorlaufing. Yes - misleading / lack of detail in the comment. I know vorlaufing takes place in big breweries and has done for years, What I was referring to was the use of vorlaufing in say 10 brl breweries, or in even large British style mash tuns. I've worked with ones producing 800+ hl brews, but not fitted with vorlauf facilities - as they weren't considered necessary with the coarse grist. Actually it would not have been possible with early tower brewery designs - , no electricity, no pumps, so it was simply dropped by gravity into the kettle. And the early UK brewpub size kit was similarly designed & built - coarse grist so supposedly no real benefit - or was it lack of imagination non the part of the early designers / builders?
    dick

  8. #23
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    Quote Originally Posted by dick murton View Post
    Re vorlaufing. Yes - misleading / lack of detail in the comment. I know vorlaufing takes place in big breweries and has done for years, What I was referring to was the use of vorlaufing in say 10 brl breweries, or in even large British style mash tuns. I've worked with ones producing 800+ hl brews, but not fitted with vorlauf facilities - as they weren't considered necessary with the coarse grist. Actually it would not have been possible with early tower brewery designs - , no electricity, no pumps, so it was simply dropped by gravity into the kettle. And the early UK brewpub size kit was similarly designed & built - coarse grist so supposedly no real benefit - or was it lack of imagination non the part of the early designers / builders?
    While I would never group pumps and electricity together since they are technology centuries apart, obviously brewing has been taking place longer than the advent of both of these, and neither is required to produce beer. The fact British equipment manufacturers did not use an engineering design that is now common place does not stand as evidence of the processes validity.

    I would argue that the very word Vorlauf in its actual direct translation refers to a process that could very well extend to a period before pumps or electricity. I'm not a brewery historian though. Since it means "before-run" and not "re-circulation" this could easily be achieved with a wort holding vessel such as a wort grant, or wort receiver, or even just a bucket (as in my personal example on a British styled pub system), and would have been possible on gravity fed breweries of nearly every design. Vorlauf is not a piece of equipment, but a process.

    I find it very possible (and almost certain) that early brewers would have seen a clarity forming as wort was drawn (as I do), and personally I don't find it a far stretch to think they may have taken this "pre-run" cloudy wort and either recycled it by bucket (or shadoof) to the top, or recycled it to the strike water of the next batch for mashing. We know as fact they did recycle low gravity wort and add it subsequent batches, so I think this is well within logical reason to think they may have done the same with initial runnings.

    Brit manufacturers may have avoided the vorlauf process for a number of reasons, but that doesn't mean that it doesn't have value (we certainly agree it is not a required process). Perhaps they were less concerned about extract efficiencies and a coarser grain allowed for faster processing. Cheaper labor or ingredients would reduce the need for ingredient efficiency. Or perhaps German brewers faced a higher probability of lauter problems due to bioglucan content and had to adapt a more advanced processing technique. Perhaps the Brit design wasn't lack of imagination, but equipment manufacturers were just being cheap (China today). Or perhaps British brewers were spiteful of German brewing techniques and sidelined the practice for that. Stupider things have happened. Maybe sheer laziness. Or maybe the new generation of pub brewer at the time was just undereducated/trained (like today) and uninformed of the benefits of setting a stable lauter bed. There are many speculative reasons why different regions brew the way they do.

    We know as a historical trait, Germans tend to be a bit anal about engineering and design principles. UK and US are more of a "rough around the edges" type who will accept less than perfect results in exchange for "increased progress" in most cases. We know the French & Belgians took the more "artisan" route in general.

    Vorlauf is a process that is not necessary, but provides a more consistent lauter, which often lends to higher extract efficiency and quicker run off times. If the process is not done correctly the opposite can occur. There is most certainly a risk/reward balance to consider. There is also evidence to suggest cloudy wort may have better long-term stability than clear wort, but I personally fine enough value from lauter times and efficiency to maintain the practice for myself. Stability has not been an issue. If you achieve good extraction and runoff times consistently without vorlauf then there is no need for a vorlauf. (You have a mash filter! - JK)

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