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Convex Kettles - Hop and Trub Problem?

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  • Convex Kettles - Hop and Trub Problem?

    Hi All,

    I've been saddled with a convex-bottomed 7bbl kettle which has left me grasping for answers about hop and trub separation post boil. A convex bottom seems totally contrary to what i've learned about brewhouse design but supposedly BBT and a few others have made similar vessels. The tank's previous life was as a batch pasteuriser in the dairy biz, in case anyone cares.

    The plan for knockout is thus: Kettle>Pump>Hopback>Basket Strainer>HEX. The hopback necessitates the use of whole hops, which has me worried about not having some trub and hop removal prior to the pump and having the pump jam. This concern comes from my thinking that whirlpool separation in the kettle is basically pointless because of that kettle bottom. It looks like I really need some sort of screen or 'hop dam' covering the kettle outlet or I risk plugging up the works. Does anyone have suggestions for a simple solution or an off-the-shelf product? The best I've come up with is adding another basket filter or a perforated SS gate contraption covering the kettle outlet.

    Perhaps I'm worrying unnecessarily, or my beer is DOOMED.

  • #2
    Agreed that whirlpool would be pointless. Whole hops would likely clog either the pump itself, or the kettle outlet/pump suction. Any small strainer in the kettle will plug during knockout. You'll need lots more surface area. Like perhaps an entire false bottom in the kettle above the convex part. Not only will the hops mat down over your strainer/lauter, but the hot break and other particulate will bind it tight against wort flow. Also, it sounds like your hopback is closed, no? Why a closed hopback and another strainer basket? Isn't that redundant? Another option, although far from ideal, is to accept over-oxidation on the hot side and strain the mess through your lauter tun--if you can pump it. Although you might be able to make this work to a certain degree, you might also like to look about the used equipment market for another kettle! One that doesn't limit your hop varieties to whole cones and funky processing. Good luck!
    Last edited by gitchegumee; 09-30-2013, 09:14 PM.
    Phillip Kelm--Palau Brewing Company Manager--

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    • #3
      Thanks for weighing in Phillip/gitche, I've seen your posts around PB and they've been incredibly helpful in other areas of setting up the brewhouse.

      The knockout is set up Pump>Hopback>Basket Strainer>HEX, with a closed hopback, because of two things - the system I have experience with is set up like that and that system works well for purpose, and my reading about the hopback supplier is that quite a bit of hop material sneaks through hopback's false bottom. In any event, the basket strainer is something I acquired for free and I can remove it from the run if it proves pointless.

      I would dearly love to not be limited to leaf hops though. I prefer leaf but I worry about limiting my versatility in this day and age of the hop market.

      I've made a couple different designs for a false bottom but two problems come up: fitting the perf sheets out the manway, and that I've got 6x 24" long electric elements hanging around which make a typical false bottom design moot :/ If anyone has suggestions, I'm all ears. A different kettle isn't in the budget unless it is the only option.

      I know there are other convex kettle out there, so how has this problem been dealt with on them?

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      • #4
        Double ouch! Didn't know you had to contend with electric elements as well! That makes it even harder to work with. Don't whole hops scorch on those? They would also be antagonistic toward any whirlpool, too. Was thinking that a whirlpool could help you even with a lauter false bottom. It would clump the hops toward the middle and it leaves the large perimeter for better drainage.
        Is there any way to draw off the kettle by gravity into the hopback before the pump? Normally you wouldn't do that due to restricting the pump suction and setting up cavitation with hot wort. But if large enough, then there would be little restriction. As in lautering and DE filtration, once you start "over-sucking" a depth filter it only gets worse--fast. An old-school hopback would work well for this. Picture a colander over a bucket. It's whole hop separation where the kettle flows directly via gravity (occasionally pumped) to the wort strainer/separator prior to being pumped through the heat exchanger. Some hopbacks are open, some closed. On larger installations, they would even sparge the separated hops to extract last wort. Other times, the spent hops & the extract contained were added to the next mash to squeeze out the last bit of extract and apparently bitterness.

        Another technique you could try is referred to as a "Moor's head" It's essentially a large, perforated cone put on a draw pipe inside the kettle. Difficult to do with a convex kettle bottom, but perhaps you could use something like a large donut perforated strainer around the perimeter. Like some homebrewers do with lautering. Both a wort strainer/separator and "Moor's head" were ubiquitous before pelletized hops. Whirlpools are actually fairly recent. Hope this helps. Glad I'm not there! Good luck!
        Phillip Kelm--Palau Brewing Company Manager--

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        • #5
          The simplest solution (although maybe not the cheapest) would be to add a separate whirlpool vessel. It doesn't have to be anything fancy. If you can find a used single wall tank (dairy etc) that is about the right dimensions you just need a few ports welded into it and you're good to go. This eliminates all that messing around in the kettle. just pump the whole mess into the WP vessel on a tangent and there you go. As you grow having this tank could help your operation save time on double batch brew days too.

          Of course this is assuming you have the space for it, access to second hand tanks and a welder who can make the mods...
          Scott LaFollette
          Fifty West Brewing Company
          Cincinnati, Ohio

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          • #6
            Hey fellas.

            I've brewed on a system with a similar kettle configuration using whole leaf hops, and we sent the hot wort through the false bottom of the lauter tun using a pop-up valve (you could maybe come in through the side, low), stirred & settled using the rakes for even distribution of leaves within the wort, then pumped out. We got good leaf removal and decent trub removal (the leaf hops serve as their own filter bed). Like Phillip indicated, the bed indeed would bind a bit, which is why halfway through we'd close the exit, stir up again with the rakes, settle a bit, and finish processing. Waste hops out through the spent grain port. Of course, this system was already set up for pumping mash after stepping using the kettle, and there was additional settling (coolship) done post-hop removal. But it also sounds to be the cheapest route, given what you've got at the moment, and maybe worth a trial? There are temporary ways of getting wort "quietly" pumped in without yet drilling new holes in the LT.

            If trub volume is greater than you'd like, you'd then likely still need to add some settling step for the finer particles. Then you're back to all the other options.

            And where the hop-back falls in, is also I suppose post-hop removal?

            Also, haven't seen it written, but your only available knockout outlet from kettle is bottom dead center I'd suppose? Can you get any kind of cone formation at all in the bottom of the kettle currently?
            Last edited by NinkasiSwain; 10-02-2013, 02:50 AM.

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            • #7
              I had to contend with this once...here's what worked for us (after a lot of trial and error)

              have a stainless ring about 6" high constructed in two halfs that fit together edge to edge (so they go in the manway)

              weld a few (we used five) small vertical tabs into the bottom of the kettle to hold the ring. The ring needs to be heavy enough that it doesn't bounce around in a good boil (1/4" stainless maybe?)

              Now you can whirlpool, and the ring holds the bottom of the trub cone in place...we also ended up drilling a couple of limber holes into the ring. If the ring is about 2/3 of the diameter of the kettle floor, and at least as high as the top of the convex dome, that will work. I found a long and relatively slow whirlpool worked best in this case, and while the beer wasn't PERFECTLY bright off the side of the kettle, it was almost as good as I get off a dedicated whirlpool now.

              The ring isn't bolted in or anything, so it's easy to lift out of the tabs and clean. We had ideas about making special whirlpool enhancing tabs on the ring, but ultimately we were too lazy to do anything more once it worked.

              Hope that helps!

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              • #8
                A couple of thoughts

                I assume you are using whole hops both in the kettle, and additionally as late hop in the whirlpool.

                If you put a mesh above the bottom of the true floor to retain the hops, then you will not boil the wort below the strainer mesh unless you recirculate the wort using a pump during the boil, so I really don't recommend this solution.

                As per your concerns about the pump - if you use a high rotation speed centrifugal pump, it is likely to smash the whole hops up enough that you will get a lot of fines carrying through and may block the hop back or simply not be retained very well. A low shear pump should be OK.

                The whirlpool effect really doesn't work with an electrical element as it breaks up the smooth rotation and flows which give the compaction.

                If using a lot of whole hops, then a whirlpool action is not particularly effective at getting a really compact trub cone as can be achieved with pellets - or at least not in the small setups I have seen. And bigger setups using whole hops in the UK simply don't whirlpool, though I accept that much of this may be down to tradition.

                If you are not recirculating back over the hop bed in the hop back, then if you can run the wort by gravity alone into a small underback for want of a better description, fitted with screen, and then pump the screened wort from the underback to the FV. You could always use removable baskets, and if the transfer rate to the hopback falls too low, simply stop the wort run into the underback, quickly empty and rinse it, or remove the clogged basket and replace with a clean fresh one, the resume emptying the kettle.
                dick

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                • #9
                  Thanks to everyone for their advice

                  I did some shopping around on electric elements and reworked the BTU/Hr calculation for the BK. Subsequently I'm reducing the number of elements which will allow a simple 2-piece false bottom. Simple perforated SS will have to do as wedge-wire plates are totally beyond our budget. The brewery owner and I did a whirlpool test on the BK just to double-check the physics, the results being that as long as there is a good hot break a decent trub cone forms but the stability of the cone is pretty weak meaning knockout with need to be stopped with 5-10 gallons still in the BK. The false bottom might even allow us to use pellets.

                  I'll try and remember to report back on results for the benefit of others once I finalize the mods to the BK.

                  Anyhow, the city just approved our conditional use permit so we can start building soon!

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                  • #10
                    @Dick Murton

                    I have to plead ignorance about the false bottom=inefficient boil-off of precursors, I don't see an economical alternative available. It is plausible to turn over the wort with a pump during the boil and I certainly will try that if our early batches present DMS or 'worty' off-flavors.

                    As for the basket filter. I did think of that, I'm proud to say. There is one in-line, post hopback, with shut-off valves should there be a blockage.

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