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Please sanity check my ideas for a gas-fired kettle design

Post #1 made 9 years ago
by Kev888
Hello all. I've been brewing on 3-vessels for a long time, but these are my first serious steps into BIAB. So, I've been reading around the forum and now wanted to check if the resulting plans are reasonable:

Volume: I want to do double corny batches (~40L) and occasionally single-keg (~50L or 13 US gallon) batches up to OGs of about 1.060 or so - as full volume mashes. It appears that a 70L (18.5 US gallon) kettle would be possible but that 100L (26 US gallon) would be more comfortable, so presumably 100L would be best.

Base thickness: I already have thin stock pots in either size, or I could buy a thicker compound-based one; reading around I gather that thin pots are okay with a well dispersed flame and have quicker heat transfer, whilst thicker-bottomed ones spread the heat better. As my burner will be reasonably well dispersed I may stay with my thin pots, HOWEVER they are really quite thin, 0.7mm (~1/32", ~23gauge), and I will be wanting to add heat to take wheat beers from a 43C (109f) ferulic acid rest up to mash temperatures without denaturing the enzymes. Under these circumstances, would anyone advise me to buy the thicker pot?

Warm air blanket: Finally, to save gas I'm going to have a shroud around the kettle, to direct hot gasses up the side of the kettle and prevent the wind blowing them away from it. This will hopefully improve heating efficiency a bit, and (being hotter than the kettle) these gasses will also prevent it losing heat from the sides too. Thats pretty tried and tested by other people for boiling kettles, but I'm thinking that for BIAB I could also use it with a (very) low heat during the mash - just enough to keep a warm blanket of air in the shroud around the kettle, and so stop the mash cooling almost indefinitely. I guess that I wouldn't need to be too accurate with the burner control, as long as the temperature differential is kept reasonably small it would take a long time for that much grain and liquor to change temperature noticeably. Does this sound reasonable?

Any thoughts or ideas would be much appreciated!

Cheers
Kev
Last edited by Kev888 on 23 Jul 2014, 19:56, edited 1 time in total.
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Post #2 made 9 years ago
by BobBrews
Kev888,
Any thoughts or ideas would be much appreciated!
Here is my thoughts that you will very much appreciate?

You know how to brew and that is 90% of BIAB, maybe 95% ? Just use your biggest pot and brew a few BIAB's so that you will have a better idea if you want in a final setup? I love your idea of shrouding the system to force the heat up the sides! The Warm air blanket idea is a winner! :clap:

I brew with a converted keg. My keggle holds 15.5 gallons or 58+ liters. I rarely use the full keggle. I still "normally" do 5 gallon brews just so I can have more variety. But the option is always there to do a double batch. Planning and dreaming are the fun part of brewing. The longer it takes to fulfill the dreams the longer the fun will last!
Last edited by BobBrews on 24 Jul 2014, 02:16, edited 1 time in total.
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Post #3 made 9 years ago
by Kev888
Great, thanks BobBrews, thats reassuring.

I like your suggestion of having a go before doing anything permanent :thumbs: I'll just buy the minimum needed and lash something up to start with. Guess the spent grain could be used to test various things out, as well.

Its a very good point on the smaller batches. I do either 40L or 80L brew-lengths on the 3vessel system but 80L is too much for some beers, which lose freshness before they get drunk. So I was happy to drop to just doing 40L/50L, but yes, it would be even better if the set-up would do down to 20L too; it may be that my 70L pot is a better compromise. Something else to test!

Thanks again,
Kev
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Post #4 made 9 years ago
by PistolPatch
Saw your post earlier Kev, my concentration is failing so I better write fast :lol:...

I have the 70 L kettle (have two of them actually) and that size works really well for two x 19 Litre Cornies. On some brews you need to add a little water before the boil but that is fine. I also single batch in them sometimes and that is fine. My ususal process is to drain half the wort into a cube (no-chill) and the other, chilled, into a 'single' batch fermentor so as I can fill one corny straight away and have another batch ready to pitch as the first corny runs out.

Anyway, that aside, my main reason to comment here was as follows. The thickness of the bottom of your pot is not much of an issue if your flame is dispersed during the boil and it seems you have that under control but...

You wrote above about keeping the burner on a very low heat during the mash. No! No! No! :). For a start in full volume mashing the heat ie retained really well - see this recent thread. Secondly, all that low application of heat will do is make the bottom of your mash super-hot (nbear-boiling) and the top of your mash cold. Any time you apply heat,you must agitate the mash.

The occasional stirring of the mash and temp check followed by a heat addition if necessary (whilst stirring) is is all you need to do in a full volume mash. Some people end up being even lazier and not doing any stirring but when starting out, the regular stir and temp checks are the best advice for sure.

:luck:
PP
Last edited by PistolPatch on 24 Jul 2014, 19:00, edited 1 time in total.
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Post #5 made 9 years ago
by Kev888
Many thanks PP, thats really helpful. :thumbs:

As it happens, I was considering no-chill cubes, but I hadn't thought how it could help split larger batches, thats an excellent idea! Perhaps I don't really need to worry too much about sizing the kettle for single batches then, unless I wanted to do small experimental recipes or something like that :think:

Thanks for the thoughts on the thickness of the pot, it sounds promising so I'll definitely try with the thin ones I have.

Yeah, I can see that any direct heating (without stirring) would be a problem. My plan for creating the warm air blanket was to turn the burner very low and put a heavy metal plate or ceramic tile over it so that only warm air reached the kettle, the ideal being that the air would be just about warm enough to prevent the mash cooling significantly rather than actually adding any heat to it. However... I don't know if that would work at all in practice, the burner could blow out too easily or be too hard to control when very low, and if it isn't even necessary then it could well be easier not to bother! I think some testing is needed really; its often considerably cooler here in winter so I'm not sure how much heat would be lost - I've done 65L mashes in an insulated MT many times, but those were stiffer mashes at 2.5L/kg, not full-volume, which presumably makes a difference. :scratch:

Thanks again,
Kev
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Please sanity check my ideas for a gas-fired kettle design

Post #6 made 9 years ago
by Contrarian
With a batch to fill 2 cornies you will end up with a total mash volume of somewhere around 65 litres depending on target gravity. The thermal mass of the water means any temp fluctuations will be small enough not to impact the brew process.

For step mashing it might be worth looking into a way you can keep the bag off the bottom. 2 common approaches are a stainless pizza tray with some stainless bolts in it or a skyhook that allows the bag to be raised off the bottom during the step.

I'd say you have ample kit to give this a go. All you need is a bag that will fit in your 70L or 100L pot and you're away although with either I those sizes it is very helpful to have a skyhook to pull the bag. 10kg of grain that is hot and wet can be a tricky dead lift!

Good luck! It's a simple way to brew but like anything brewing you can also make it as complicated as you want!

Post #7 made 9 years ago
by PistolPatch
I think the warm air blanket is a great idea but you won't need the flame on as the heat shields (your warm air blanket) will exaggerate the thermal mass Contrarian mentioned. On my double batches in summer, I can turn my flame off, stir my strike water (and/or mash), take the temperature, wait a few minutes , stir again and find the temp has risen!!!!

The heavy base of my kettle and it's stand means that the heat is stored in those and continues to disperse after the flame is off.

So we are sort of getting back to what Bob said about doing a brew or two first. I highly recommend 'paying attention' in a situation like this and one of the best ways to force yourself to pay attention is to agitate the mash and take its temperature several times during the mash until you get a feel for the physics of your equipment.

Double batching is great when you no-chill half the batch but it also means you brew a lot less which is starting to annoy me now. I have four cubes here over a year old that I still haven't pitched! (They'll be good though!)

:peace:
PP
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Post #8 made 9 years ago
by Kev888
Thanks for the thoughts, Contrarian, very helpful.

Your volume of 65L is good confirmation of what I'd imagined; it would come close to filling my 70L pot (potentially more if I wanted higher gravity or my efficiency was lower than expected). So my inclination would be to use the 100L pot unless there's any reason not to; I know that I could top up after removing the grain but (unless a full-volume mash is different to thicker/stiffer ones) its probably nice to have a bit of headroom for doughing in.

Yeah I was going to use a bit of very open stainless mesh to keep the bag off the bottom. Although, as I'm going to be directing hot gasses up the side of the pot as well it could perhaps benefit from something keeping it off the sides too, so I'm considering a mesh basket in the longer term - either a fairly course one with the bag inside it, or possibly one of a fine enough mesh to replace the bag.

The weight of the wet grain is a good point; I can lift that much wet grain when its drained but it doesn't sound like much fun, and I guess it would be even heavier until it drains fully. So some sort of pulley seems like a very good idea, but being outdoors I'll probably have to make some sort of frame to support it, so to get me going I will probably just scoop some of the grain out with a sieve to begin with. I see that some people use two or more bags, but I want to make stirring the whole volume as easy as possible so I'd prefer to just have one big one.

Ha, yes, I need to be careful here; one of the things that appeals to me about BIAB is the elegant simplicity, so I must resist my natural inclination to over-complicate it. I don't really mind if I spend a bit of time building the set-up, but I want the brewing process to be both simple and easy.

Cheers
Kev
Last edited by Kev888 on 25 Jul 2014, 17:53, edited 1 time in total.
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Post #9 made 9 years ago
by Kev888
PP, thanks very much once again. I'd not thought how the air gap within the shroud/wind-shield would be insulation in itself, without being heated; you have a very good point there, this could be simpler than I'd imagined!

I'll definitely just lash something up to begin with and see how it works out, though I may make some things that I know will be needed whatever, like a decent stand for the burner. Sadly its mid summer here at the moment so its not the best time to test heat loss; it doesn't normally get 'really' cold here but it has been down around -20C on a brew day before now which is probably about the worst I'd expect, at least without brewing at night!

Sounds very encouraging about the cube shelf life; do the filled cubes have to be kept cool to last that long? I've been trying to store finished beer for several months, it works but takes loads of costly cornies and the beer looses hop aroma etc, storing the wort instead seems much better.

Cheers
Kev
Last edited by Kev888 on 25 Jul 2014, 17:55, edited 1 time in total.
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Post #10 made 9 years ago
by PistolPatch
Kev888 wrote: I will probably just scoop some of the grain out with a sieve to begin with.
Wow! What a clever idea.

I have never heard or thought of that before. Unnecessary in a lot of set-ups but a golden idea in many others!!!

:clap: :clap: :clap:
Last edited by PistolPatch on 25 Jul 2014, 19:13, edited 1 time in total.
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Post #11 made 9 years ago
by Kev888
Thanks! Glad it doesn't seem silly. If it works well enough then it could become one of those temporary fixes that lasts for years. :evil:

Part of the reason for all this is to drastically reduce the space all my brewing kit takes up and the facilities/services I need to brew, so not needing winches and A-frames or similar would be quite useful.

Cheers
Kev
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