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Domed False Bottoms - How Domed Is Too Domed?

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manticle

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I've done a search on domed false bottoms but get mostly marketplace threads.

Sorry if the answer is in front of my face - I've been unable to find it.

I currently use an esky with copper manifold but am considering making a tun from a 40 or 50 L aluminium pot (4mm, same as I use for my HLT).

I have 2 stainless steel bowls (catering/hospitality grade) that fit perfectly inside my HLT. I am thinking about cutting thin, radial slots in one of those (way too big for my kitchen) and running a copper pick up tube through it which attaches to the tap. Tube would run presumably through the side, not the centre top, so it has no bearing on placement of the tap.

I know you can by SS mesh domed false bottoms but they have far less of a dome than the bowls I mean which would be at least 100mm deep at the apex.

Are there any issues I should be aware of before trying this? Is there such a thing as too domed?

Currently batch sparging, gravity feed if that makes any difference - still keen to know about fly and pumped for future reference.

Cheers
 

Helles

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Not sure about the domes but not seeing a problem
Other then taking up mash space
Maybe try a bazooka under bowls instead of copper pick up
Being as slots maybe too big no matter how you cut them ( angle grinder)??
 

manticle

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Thanks for the reply. Mash space shouldn't be a problem as I'm mainly single batch anyway.

Sorry for the stupid question but what do you mean 'bazooka'? (besides the anti tank weapon)

Slots would probably be cut with a dremel, similarly to my copper manifold so quite narrow. Otherwise smallest wheel I can fit onto my angle grinder.
 

Helles

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One of those mesh screen filters
Just had look at Bazooka on G&G not what i was thinking about $59
The one i brought from G&G was About $10 And about 6 inch long but all mesh
I use it as a kettle screen
Sounds right for under FB if holes could be too large
If that is the way your copper pick was going to be ( i seen this as a manifold type pick up)
 

hoppy2B

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G'day Manticle,
I cut the top of an 18 gallon keg and have been trying to straighten it to use as a false bottom. Not easy. <_<
So far I have cut slots around the perimetre to help make the job of bending the metal easier. I've been wondering if I should cut slots in the middle of the dome as well. A consideration would be whether the dome will channel liquid to the outer edge and through the slots.
I'll be leaving a bit of a gap to retain the name of the brewery etc which is stamped around the lid if I do decide to cut slots in the middle. That should help to maintain some strength in my false bottom, as it may have as much as 50kg of grain on it.
 

manticle

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Maybe you don't need to flatten it? Most kegs aren't massively dome shaped - just a slight curve. I would have thought it would be perfect as is. I'd use the top from my keggle but I stupidly threw it away when I first cut it out.

My slots will be radial converging towards the centre - should retain enough strength to resist the weight of the mash.

EG. _\I/_


Stupid forum won't let me align the bottom section. All the way around, more slots, that pattern.


Have you got any photos of what you mean?
 

Helles

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I think i might have bottom of a keg cut out at work( not sure)
Could be about 10-12 inch round
If you want it you can have it
Ill have a look on monday
 

Thirsty Boy

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Assuming a continuous sparge - depends on how deep your mash bed is likely to be - if the dome is high, the bed will be significantly thinner at the top. Thinner bed, less resistance to flow through that bit, path of least resistance is where the liquid will flow. Result - over sparging in the region above the dome and under sparging everywhere else. The higher the dome relative to the depth of the mash bed, the worse the potential problem.

Assuming a batch or similar type sparge - it doesn't matter diddley.
 

manticle

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@TB:

OK cheers.

So my current setup/process will be fine but if I move to continuous in future, I should consider a much flatter FB.
Just what I needed to know.

@Helles: Cheers mate- let me know.
 

hoppy2B

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My keg is an old out dated one. The bottom and top were recessed if that makes sense. There is no way I could have used it as is when I cut it off. I'll try and put some pics up tomorrow.
 

jyo

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I was actually eying off the good lady's SS bowl thinking the exact same thing as you before I bought my false bottom.

A mate who hacked up a keg for me yonks ago made a falsie out of the bottom of an old keg that I still have sitting around. Manticle, you, or anyone else who wants to pay for postage/pickup are welcome to it for a cuddle. You can see in the middle a thick plate of SS has been welded, you just need to drill your hole here for a 90' barbed elbow pickup.

Cheers


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hsb

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There's a section in Palmer on the fluid dynamics of mash Tuns.

I've got 3 keg lids leftover if anyone wants one.
 

Wolfy

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I have 2 stainless steel bowls (catering/hospitality grade) that fit perfectly inside my HLT. I am thinking about cutting thin, radial slots in one of those (way too big for my kitchen) and running a copper pick up tube through it which attaches to the tap.
A stainless steel (camping) type plate or platter would be a better option if you had one, and would work well for batch of fly sparging.
Rather than cut-up a bowl, a SS braid from the green-shed is likely to cost about $6 and do a more than adequate job for batch sparing. In addition to what TB said, due to the steep-dome-shape, I can imagine a situation where the grain 'stuck' down the sides of the bowl at the bottom of the pot, might be difficult to mix/stir and you might get pockets of unmixed or relatively unfiltered grains.
 

QldKev

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The bowl would work, the only issue I can see is being tallish and fairly light you may bump it easily when stirring the mash and let too much grain underneath.

My false bottom is a domed keg bottom, with slots cut with a grinder using the finest cut off disk I could find. I love it, no issues with clarifying the wort and never had a stuck mash even with the march pump running with the valves fully open.

false_bottom.jpg

My pickup is through the side of the false bottom. Normally I would just go through the top using a 90 elbow and via a hose tail into some heavy duty silicone hose to the tap. Then for clean ups just pull the hose off the hose tail and remove the false bottom. Mine is through the side of the bottom as it houses a temp probe that sits directly above the concealed element (internal RIMS). I pull the entire assembly out the side using a compression fitting. Also I have kept some height around the false bottom to clear the concealed element, which you would not need to worry about.


I would jump at the offer from jyo.

edit: For size reference, my mash tun is 100L.


QldKev
 

MHB

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For the cost and its a once in a lifetime expenditure, I would seriously consider a commercially made domed false bottom.
Try to choose one that is 50-100 mm smaller than the inside diameter of your tun for the best flow dynamics.
Mark
 

manticle

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All things to consider.

I'll let you know JYO - can you measure the diameter for me?

I guess a good part of the attraction of using stuff like SS bowl (or buying something similar but flatter and cutting the slots myself) is the fun of manufacturing stuff yourself. Stainless braid has never excited me much wolfy - I'd probably look at making another copper manifold (possibly round) to suit before going that route.

Additionally, while I will continue batch sparging for a while, it's nice to have the future option that what I make is going to work well.

QLDKev - looks just like what I had in mind but a bit flatter (yours is flatter I mean).

MHB: are there commercial varieties you'd recommend over others? Whether I buy it or make it, the design will be inspiring. I know there's a few around but I've seen some of the perforated ones collapse in a high gravity mash (resulting in stuck sparge). I think the bowl is much closer to the edge than 50 mm* so that's also something for me to consider.

* Closer to the edge of my HLT which I was considering as the right size for my tun. I may consider a broader, shallower pot for the tun though as my understanding is that a shallower grain bed works better than a deeper one. The dome would become even more of an issue in that circumstance I would guess.

I won't be brewing for a few weeks while I move and hope to take the opportunity to get the new system set up (been dilly dallying because I tend to brew rather than build when I have the time free) so I have plenty of time to design what I aim to do.

Thanks
 

MHB

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Being in from the edge avoids channelling; it's just so much easier for the wort to travel down the wall than through the bed that it's worth making the wall path longer to compensate.

Mainly it's about Void Space, the total area available to filter wort through. Good Perforated Plate should be about -⅓ not there so a 20cm FB would be presenting a 7800 to 10,000 mm2 void and that's very evenly distributed, to get the same with a 1mm slit it would have to be 7.8 to 10 meters long. If you haven't done much metal (particularly Stainless) cutting it's a prick of a job.

If you were making cuts in a 200mm dome and you used 3 lengths for obvious reasons, the average length would be (say 80, 60 and 40mm long) 60mm that's 130 to 166 cuts or one starting in every 4-5mm around the circumference.

I really think the commercial domed ones work a lot better than any other option, you really notice the difference when you sparge (Fly but that's redundant) if you only ever want to batch sparging its pretty much irrelevant what you use.

Mark

Trying to fix formating
M


 

manticle

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Being in from the edge avoids channelling; it's just so much easier for the wort to travel down the wall than through the bed that it's worth making the wall path longer to compensate.

Mainly it's about Void Space, the total area available to filter wort through. Good Perforated Plate should be about -⅓ not there so a 20cm FB would be presenting a 7800 to 10,000 mm2 void and that's very evenly distributed, to get the same with a 1mm slit it would have to be 7.8 to 10 meters long. If you haven't done much metal (particularly Stainless) cutting it's a prick of a job.

If you were making cuts in a 200mm dome and you used 3 lengths for obvious reasons, the average length would be (say 80, 60 and 40mm long) 60mm that's 130 to 166 cuts or one starting in every 4-5mm around the circumference.

I really think the commercial domed ones work a lot better than any other option, you really notice the difference when you sparge (Fly but that's redundant) if you only ever want to batch sparging its pretty much irrelevant what you use.

Mark

Trying to fix formating
M


Done a bit of metal cutting. Wouldn't call myself an expert by any means. Noted about the channelling - I know it's relevant to manifold design but hadn't considered it might also be relevant to false bottoms.

So this is the main design you are referring to?

http://www.craftbrewer.com.au/shop/details.asp?PID=926

OR

http://www.grainandgrape.com.au/product_in...roducts_id=6987

@JYO: Cheers. I'll let you know.
 

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