How does mash tun shape affect efficiency?

[jceg316]

When I started all grain brewing I bought this lauter tun: http://www.the-home-brew-shop.co.uk/acatalog/Lauter_Mash_Tun.html#.VwYs46QrJhE and wrapped it 4x in insulation foil. Towards the end of its life I was getting 75-80% efficiency.

I upgraded to this stainless steel 50 litre: http://powellbrewing.co.uk/index.php?route=product/product&path=60&product_id=56 and my efficiency dropped massively, probably around 65-70%. I started doing 90 min mashes and my efficiency shot back up to 80%.

Just to add, I did the same size brews in both ~20L and the stainles steel setup is a HERMS. Sugar isn't being lost in the HERMS though as I run the sparge water through it. I fly sparge with both.

My question is, what is it about the mash tun that would lower my efficiency?

TIA

 

[Covrich]

Could be a few things I guess... are the temps calculated the same? are you using the same water grain ratio??

Is there anything different such as doing biab or do you just mash in there and drain off..

Not sure really I use a 50L pot from powell similar to what you have.. but I do it all in one BIAB with a big bag mash out no sparge and I get 70-75% with that.

 

[Leon103]

Time if the brew shouldn't rally effect efficiency. Don't most of the conversion happen at the beginning of the mash?

 

[jceg316]

Temps are calculated the same and neither were BIAB, both were normal mashes, then fly sparge.

I kept water/grain ratios the same but as there's a big gap between the false bottom and real bottom in the SS vessel, I upped the water/grain ratio. But surely HERMSing would account for that? It wasn't upped hugely either. Instead of 1kg/3l it was 1kg/3.1l.

Mash time shouldn't affect efficiency in most cases, but it really helped mine.

 

[cheapbrew]

Mash time can definitely affect efficiency

http://www.braukaiser.com/wiki/index.php?title=Understanding_Efficiency#Time

 

[Richie_asg1]

If there is a big gap between the screen and outlet is it possible that is dead space so is just plain water in there?

Also you have moved from plastic (insulating) to steel (conducting) so may affect the thermal gradient throughout the mash maybe?
You certainly won't be heating it the same way.

And lastly - are you using the same thermometer?

 

[jceg316]

I'm not sure there would be water below the screen. As it's a HERMS the wort gets recirculated so any water would be drained and mixed back on top of the mash.

I'm not using the same thermometer to mash, this SS setup is far more accurate than my plastic one as I have a built in thermometer. Plastic one I had to take the lid off and use a spirit thermometer. Plus I have the thermometer on kettle and brew controller for the HLT which tells me temps during recirc.

 

[Spoon]

I'd say two thing's are sub-optimal from and engineering perspective (this is based on engineering theory learnt from big process columns, it may or may not actually work in brewing). Wall effects are a big deal in distillation columns, I suspect I'm overplaying their importance on grain beds where the grains are much much smaller than the tun diameter (packed column packing would typically be 10-100th of the diameter, grain is more like 100-200th even in a small homebrew bucket).

1) Foil backed bubble wrap is actually a pretty poor insulator. It's intended to be fitted facing an air space so it can reflect head back in (or keep it out), it's not anywhere near as good as a closed cell foam. And example of where it works well would be under your car windscreen (solar radiation hits it, most of it reflects back out the car, and the insulation is just shielding the remainder), or in an attic/loft space, fill the gaps between the rafters agaisnt the tiles with kingspan or similar, then cover that with the foil, you wouldn't put it against the tiles then kingspan over it as like putting it against the brew pot, there's no radiation to reflet.

2) False bottoms should be undersized. If they're the full diameter then liquids find it easier to travel down the side of the vessel (imagine the grain as a load of spheres, which is easier a 2D zig-zag down the wall, or a 3D zig zag through the middle?), slightly undersizing the false bottom draws liquid away from the walls, preventing channeling down the sides and over extraction from those grains. The ideal from a fluid flow perspective would actually be rings on the walls every so often and several false bottoms and grain beds so that the flow got redistributed away from he walls. HEMS kind of achieves this by returning liquid from the bottom to the top, thus you can't over extract because all the grains are being soaked in the same sugary wort. How much under size is needed? No idea, I went for a 1" gap all round (false bottom is 2" smaller than the bucket), reasoning that lower efficiency from the hidden grains in the corner is offset against decreased risk of oversparging and tannin extraction.

Geometry of the pot will have an impact (height Vs diameter), a tall thin pot both restricts flow (higher flow, the bed isn't mechanical tough enough and compacts leading to a stuck mash), It also means you have sparge water over extracting at the top before it picks up sugars lower down, not ideal. A smaller diameter also has greater wall effects (see point 2 above) due to the surface area to volume ratio. A 'pancake' shaped tun isn't ideal either, very difficult to get even distribution of flow, very difficult to manage the sharp cut off between sparging sugars and overextractining tannins. Somewhere between the two will be a theoretical idea. I think there's a paper covering it (Institute of brewing and distillation?).

Short fat
- less tannin extraction during sparging
- more chance of sparging for too long
- no wall effect

Tall thin
- more tannins extracted during sparge
- easy to judge when to stop
- increased wall effect

 

[MyQul]

Wow what a fantastic post, spoon! I dont use a mash tun just my pot but even so your post is fascinating. Think you've covered everything the OP needs to know - thread closed :lol:

 

[user 15657]

Think you've covered everything the OP needs to know - thread closed :lol:

Lock in! :grin:

 

[jceg316]

@Spoon, thanks for the detailed response, I do have a few questions:

1. Insulation foil is basically bubble wrap made of tin foil. Do the air pockets not do much with insulating the heat?
2. I've read that sparging slowly will avoid channeling along the walls. As my mash tun is wider than it is tall I can afford to sparge slower without tannin extraction.
3. I don't quite understand what you mean by

imagine the grain as a load of spheres, which is easier a 2D zig-zag down the wall, or a 3D zig zag through the middle?

Thanks for taking the time to write this response though. Otherwise it makes sense.

 

[MarkMayf]

This should help:



The black is the vessel wall, the brown the grain, and the blue the water channelling down the zig zags.

 

[JapanBrew]

Excellent write bud!!!

 

[geetee]

I posted late last year that mash tuns should be shorter and wider and had done trials on some in Brewlab setting where these proved to have the most efficiency. Look at any Microbrewery and you can see the shape of the mash tun.

Great description Spoon and definitely backed with evidence that I have seen.

 

[Spoon]

1. Insulation foil is basically bubble wrap made of tin foil. Do the air pockets not do much with insulating the heat?

They do, but the foil backed stuff isn't helping. It's mostly paying for something that looks better.

The more 'bubbles' the better the insulation, as within each bubble the air is circulating freely, a bit like the difference between a cavity wall in a 60's build house, and cavity wall insulation (the insulation creating millions of small cells where there was only one before).

2. I've read that sparging slowly will avoid channeling along the walls. As my mash tun is wider than it is tall I can afford to sparge slower without tannin extraction.

Sparging slowly allows the sugars to dissolve into the water and changes the pH which prevents tannin extraction. If the tun is too tall (or the gain bed too deep) then the first bit of grain is always being rinsed in fresh water. It's an unavoidable factor in the design, but a short/fat tun has much lower velocity than a tall thin one for the same flow rate so has an advantage.

But then short fat tuns have other issues, and there are practical issues too, like ensuring the top of the grain bed is flat, and the bed is an even density, etc, these will be far harder on a short/fat bed. So an idealized tun is going to be a compromise between a lot of factors.

Remember that breweries don't have different tuns for different beers, so it's perfectly possible to brew a 2% farmhouse ale with a tiny grain bill in the same tun as an imperial stout, giving completely different geometries to the grain bed. One will just be less ideal than the other. The shorter grain bed will need careful watching of the wort coming out to avoid oversparging. The taller grain bed will need very low flow-rates to avoid compacting the bed (but tannin extraction won't be an issue even though the bed is taller/thinner because you'll be stopping long before the sugar content has dropped and the pH starts to rise, but might be an issue if you use the 2nd running's for something else.)

3. I don't quite understand what you mean by

It takes less energy for the water to channel down the side between the flat wall and 1 layer of grains than it does through the grain bed itself, it's a combination of the gaps being bigger because the grain can't pack neatly like a jigsaw, and there's one degree of freedom less as the water can only turn left/right, it doesn't waste energy going in/out. The net result is liquid flows fastest down the walls of a packed column/bed/mash tun.

As MarkMayF's diagram shows, if there was another layer of grain it would leave some very small gaps for the wort to move through.

 

[JapanBrew]

So, either pay close attention to the gravity of the wort coming out during sparging or, if you're doing different size batches, have different size mash tuns. Makes sense. I have been contemplating buying another smaller pot for that reason. But, recently I've been getting out of this world efficiency so .... "If it ain't broke don't fix it!!"

 

[JapanBrew]

I just remembered about a guy who made a recirculating mash tun that was like a hop rocket. He forced the liquid from the bottom up through the grain and then back to the bottom. So with physics in mind, that is the ultimate way to do it. The slow speed at which the liquid is moving up through the grain, isn't enough to overcome the weight of the particles. Therefore shifting it around and settling.
But the negative is, he spent so much time on it and only got a few extra points up on efficiency that I wonder if was worth all that!?!? Most of us, even the simplest mash tuns, get good wort! Really I'm not taking the **** out of Spoons work. I love it. I'm a wonky guy!! I could read that stuff all day. (Trust me, I have... GF got PRETTY ******)

What's the moral of my message????

Don't brew a 9.5% IPA, consume a few of them and then hit the message board!!!!

 

[Spoon]

But the negative is, he spent so much time on it and only got a few extra points up on efficiency that I wonder if was worth all that!?!? Most of us, even the simplest mash tuns, get good wort!

I think that's the most valid point, as homebrewers we could do no-sparge BIAB mashes and probably still end up saving money versus buying "the best" kit.

Case in point, you can buy an off the shelf, all stainless steel, sight glassed, re-build-able linear action ball valve, 8 gallon mash tun for over �£300

Mine is:
�£10 33l bucket
3x �£1.99 yoga mats and a roll of duck tape
�£12 of plumbing parts from screwfix
�£12 false bottom
=�£40

�£250 in change would buy another 250kg of pale malt. For a 5% jump in efficiency that would take me 625 brews, or 25,000 pints of homebrew to pay that back!

I've never brewed outside of homebrewing, but I'd not be surprised if the mega-breweries do all sorts of cool stuff to eek out performance from their mashes, because to them even small gains are big �£�£�£.

 

[MarkMayf]

I've never brewed outside of homebrewing, but I'd not be surprised if the mega-breweries do all sorts of cool stuff to eek out performance from their mashes, because to them even small gains are big ��£��£��£.

I have never seen a big scale brewery, but they must look more like chemical processing plants than the wooden mash tun types you visualise for a craft brewery. I suppose ultimately all we are doing is controlling a chemical reaction.

I'm picturing DCS systems, automated valves and pumps, huge steam plant, oodles of stainless steel, big safety systems etc.

 

[Spoon]

I imagine they probably monitor gravity and pH of the mash through out the depth of the grain bed in real time so they cans see when the grain bed is becoming depleted of sugar and the pH starts to rise.

Likewise I bet their fermentation schedules are far more involved, on-line chemical analyzers looking for diacetal/esters/phenols and tweeking the temp to keep it as fast as possible without affecting flavor. We all know Carling doesn't go through a 6 month Larger!

I did once know a guy who got the decimal point wrong whilst working at Bulmers and accidentally put 10x more orange dye in the cider (which then lead to it being BOGOF everywhere, all summer because they had to quickly brew up 10x more batches to dilute it!).