Is the dead space really a problem when doing a full volume mash?

[kohalajohn]

I have a Brewzilla So I have a solid wall mash pipe instead of a bag. And that means that the wort between the walls of the pipe and the outside of the machine, does not move around much. Can be called "dead space"

And it's a surprisingly large amount. Since it's on the outside, geometry evidently tells us that it's a lot of volume. Liters and liters of it.

But is this a problem? Some online say it is. Some AIO owners lift and lower the pipe. You have to be careful with that, with a Brewzilla as our bottom plate is loose and lowering too fast will upset it and pour out grains. But you can do it. And that would certainly mix up the waters nicely.

My last batch I followed some advice and directed the recirc hose into a lifting hole and did a brief recirc in the dead space that way. But that was also a hassle, as the wort just ran down one section and I had to keep rotating the pipe to get at all of it.

And tonight, after my second sip of whisky, I suddenly wondered if it's even a problem.

ok, so this strike water in between the walls is not actively involved with the grist. It's not doing the job of saccharification.

But in a full volume mash, who cares. I sometimes do a 6 liter pour over, instead of a full volume. That sparge water never did any saccharification work at all. And that's fine.

Seriously, is this dead inner wall space thing, actually a problem?

Thanks in advance for your input. Picture below, as we all like pictures

 

[doug293cz]

If you don't homogenize all of the wort prior to lifting the malt pipe for the last time, the wort retained by the grain after draining will have a higher sugar concentration than the wort you collect. This will reduce your mash (specifically lauter) efficiency.

Brew on

 

[kohalajohn]

Doug,

Ok, I get it.

Follow up question. Doing a couple of lift and lowers will homogenize the wort, so I get that. But what about stirring? With 60 minutes of recirc, I would think that the river of hot wort running through the bed would remove any need to stir the wort. Is that theory right or wrong?

 

[Miraculix]

Doug,

Ok, I get it.

Follow up question. Doing a couple of lift and lowers will homogenize the wort, so I get that. But what about stirring? With 60 minutes of recirc, I would think that the river of hot wort running through the bed would remove any need to stir the wort. Is that theory right or wrong?

That should homogenise it. But all the dripping and dropping will also introduce a lot of oxygen. Bad trade off, if you ask me.

 

[Peebee]

Using an AIO as a BIAB substitute (excellent choice! I use my Grainfather in "full-boil-volume-mash" mode; at least it IS then an "all-in-one" and not pretending to be one with a sparge water heater lurking in the corner) means there is no "dead space". The only liquid that doesn't make it from mash-tun to boiler is that absorbed by the grain.

But, as Doug mentions, how effective your recirculation is will have an impact on efficiency. If you give a damn for that, but I've always been troubled by suggestions that "full-boil-volume-mash" has bad efficiency. Seems good or bad efficiency depends on how effective the recirculation is (and Grainfathers are particularly good?).

So: Is it a problem? Well ... No! Unless you are particularly paranoid about "efficiency" ... and in that case the "problem" must be with you and not the Brewzilla.

 

[Peebee]

If you like piccies ...

This is one I chalked up of a "AIO" a while back, discussing locations for temperature probes. Note an AIO is effectively "RIMS".

 

[mashdar]

I have a BZ gen4 and I do full volume mashes for normal (1.050~) beers. The water around the pipe helps keep the mash temp uniform, but is otherwise the equivalent of topping up water. It surely hits efficiency, but I'm not very worried about $3-$6 of "waste"* on a batch.

7 gallons water + ~12 lbs of grain leaves about an inch between liquid level and the pipe lift holes.

I manage low 70s efficiency into the fermenter, which I'm fine with.

*On malty beers, I suspect less sugar efficiency at the same OG means more malt flavor. I don't necessarily think of that as a negative.

 

[Dave C01]

I have a Brewzilla So I have a solid wall mash pipe instead of a bag. And that means that the wort between the walls of the pipe and the outside of the machine, does not move around much. Can be called "dead space"

And it's a surprisingly large amount. Since it's on the outside, geometry evidently tells us that it's a lot of volume. Liters and liters of it.

But is this a problem? Some online say it is. Some AIO owners lift and lower the pipe. You have to be careful with that, with a Brewzilla as our bottom plate is loose and lowering too fast will upset it and pour out grains. But you can do it. And that would certainly mix up the waters nicely.

My last batch I followed some advice and directed the recirc hose into a lifting hole and did a brief recirc in the dead space that way. But that was also a hassle, as the wort just ran down one section and I had to keep rotating the pipe to get at all of it.

And tonight, after my second sip of whisky, I suddenly wondered if it's even a problem.

ok, so this strike water in between the walls is not actively involved with the grist. It's not doing the job of saccharification.

But in a full volume mash, who cares. I sometimes do a 6 liter pour over, instead of a full volume. That sparge water never did any saccharification work at all. And that's fine.

Seriously, is this dead inner wall space thing, actually a problem?

Thanks in advance for your input. Picture below, as we all like pictures


View attachment 878291

I wouldn't think it's a problem.
I would think that the liquor outside the malt pipe would be subject to some degree of recirculation, after all the wort recirculating through the grain would be subject to the resistance of filtration and the liquor outside the malt pipe isn't.

 

[Brewer Mike]

Why doesn't the liquid outside the pipe get recirculated? There should be less resistance, not having to travel through the grain bed.

 

[kohalajohn]

That should homogenise it. But all the dripping and dropping will also introduce a lot of oxygen. Bad trade off, if you ask me.

Yeah, and speaking of oxygen, the method of shoving the recirc hose into the pipe lifting holes, means you are introducing a lot of oxygen. The hole is of course above the level of the wort, so it is spraying against the outer wall and then splashing down the empty space before hitting the wort. It would introduce more oxygen than the lift and lower method

 

[kohalajohn]

Using an AIO as a BIAB substitute (excellent choice! I use my Grainfather in "full-boil-volume-mash" mode; at least it IS then an "all-in-one" and not pretending to be one with a sparge water heater lurking in the corner) means there is no "dead space". The only liquid that doesn't make it from mash-tun to boiler is that absorbed by the grain.

But, as Doug mentions, how effective your recirculation is will have an impact on efficiency. If you give a damn for that, but I've always been troubled by suggestions that "full-boil-volume-mash" has bad efficiency. Seems good or bad efficiency depends on how effective the recirculation is (and Grainfathers are particularly good?).

So: Is it a problem? Well ... No! Unless you are particularly paranoid about "efficiency" ... and in that case the "problem" must be with you and not the Brewzilla.

 

[kohalajohn]

The idea of accepting a slightly lower efficiency is a common theme in the AIO community.

I think I now understand the move toward AIO. It's a deliberate trade off between a small loss of efficiency and a huge gain in ease of use.

Everybody in the community talks about efficiency so much, I initially thought that that was the goal, to maximize efficiency. But it's not. Doug has a massive understanding of the science behind efficiencies, but he does full volume.

So its important to understand your efficiency, so you have consistency and replication and improvement. You know that you are getting 74% not 84% and that's fine, that's just a piece of information, like temperature etc.

But we're not a commercial brewer. We don't have an accounting department yelling at us about profit margins. A commercial brewer would love to have the freedom that we have.

 

[doug293cz]

I wouldn't think it's a problem.
I would think that the liquor outside the malt pipe would be subject to some degree of recirculation, after all the wort recirculating through the grain would be subject to the resistance of filtration and the liquor outside the malt pipe isn't.

Why doesn't the liquid outside the pipe get recirculated? There should be less resistance, not having to travel through the grain bed.

Unfortunately, fluid dynamics cannot be understood with intuition. Unless you do something to force recirculation of the water/wort between the malt pipe and the vessel wall, it will be almost completely stagnant during the mash. This phenomenon is well understood by those who have studied or worked with real life fluid dynamics.

You can easily test this out yourself: Run your mash with recirculation returned only to the top of, and inside the malt pipe. At the end of the mash, take an SG sample of the wort between the pipe and vessel wall, and another SG sample from the wort inside the pipe above the grain bed. Compare the SG values.

Brew on

 

[doug293cz]

Doug,

Ok, I get it.

Follow up question. Doing a couple of lift and lowers will homogenize the wort, so I get that. But what about stirring? With 60 minutes of recirc, I would think that the river of hot wort running through the bed would remove any need to stir the wort. Is that theory right or wrong?

If your recirc is done in a way that does not have any channeling thru the grain bed, then stirring the grain bed is not necessary. But with a malt pipe, and only returning wort inside the malt pipe, does not involve the wort between the malt pipe and vessel wall in the recirculation, so it is not homogenized with the rest of the wort.

Brew on

 

[doug293cz]

That should homogenise it. But all the dripping and dropping will also introduce a lot of oxygen. Bad trade off, if you ask me.

Yes, if you want to do LoDO in an AIO with a malt pipe, and maximize efficiency (to the extent you can with no-sparge), then lift & lower is not an acceptable method. You need to split your recirculation between inside the malt pipe, and between the malt pipe and the vessel wall. All recirculation returns need to be under the surface of the liquid so that you don't entrain air.

Brew on

 

[kohalajohn]

Doug, a follow up question about how to fix it.

I get that the interwall wort is stagnant, and I get how this causes some decrease in efficiency.

But I don't want to fix the efficiency issue if it means overly oxegenating the wort.

So what's the best way to fix it without oxygenating the wort?

I think the lift and lower is less harmful than sticking the recirc hose into the lifting hole.

And if I"m going to lift, it would be best to lift just before the level where the bottom of the mash clears the wort.

High enough so all the interwall wort is mixed. But not so high there is six inches of air space, with wort splashing down and oxygenating the wort.

I think I'm going to take measurements and find out. It would be great if the lower "lift steps" happen to be at the right height for this.

Has anyone else dug into this?

 

[doug293cz]

So what's the best way to fix it without oxygenating the wort?

The best way would be to split the wort return between inside and outside the pipe, with the wort being returned below the surface of the liquid. For the outside return, you want to angle it to get a mild whirlpool action to be sure that all of the wort outside the pipe gets well mixed. You would also want a floating mash cap both on the inside of the pipe (circular) and outside of the pipe (annular ring.)

I think the lift and lower is less harmful than sticking the recirc hose into the lifting hole.

Depends a lot on the specific details of each method. Not sure that a blanket statement is possible.

And if I"m going to lift, it would be best to lift just before the level where the bottom of the mash clears the wort.

Yes, keeping the bottom of the malt pipe (and any perforated portion of the pipe) just under the surface of the wort during the lift should minimize O2 exposure during a lift & lower. However, lifting the pipe will suck air into the grain bed to backfill the space vacated by the wort.

Brew on

 

[kohalajohn]

Right.

A long thin tube into the interwall space, and down below the level of liquid, and angled to whirlpool. That's the way. for me, anyway.

 

[hungupdown]

Why doesn't the liquid outside the pipe get recirculated? There should be less resistance, not having to travel through the grain bed.

The Brewzilla g3.1.1 maltpipe has a solid wall. The g4 maltpipe is perforated for

If you don't homogenize all of the wort prior to lifting the malt pipe for the last time, the wort retained by the grain after draining will have a higher sugar concentration than the wort you collect. This will reduce your mash (specifically lauter) efficiency.

Brew on

At end of mashing. The sugar density in the wort, can never be higher than of the liquid within the grain. But levels get closer the longer the mash, when sugars have more time to diffuse. Ideally they would become equal.

Using a grain absorbtion ratio of 0.8kg / litre. In say a 20L batch with 4kg grain, 3.2L will be absorbed. So a full volume mash would need 23.2L mash water, or 28.2L with 5L boil off. Giving mash water + grain volume = 30.22L
I suspect more wort is trapped, if you include that adhering between grain surfaces, but not sure if absorbtion figures factor that in (or if its after squeezing, or when left a few hours to drain).

If all the water was utilised during mashing, then on draining and getting 25L:
Fraction of wort left in grain = 3.2 ÷28.2 =11% Maximum ideal efficiency = 89%

The BZ g4 35 L, has a 14mm gap outside the malt pipe, with average gap circumference of (272+7)*3.142 = 877mm.
The 30L mark, is 340mm above top of the malt pipe perforations.
With 30.22L its about 342mm. So the dead water volume is: 342*14*877 = 4199076ml or 4.2L
Fraction of utilised wort in grain = 3.2 ÷(28.2-4.2) =13% Maximum ideal efficiency = 87%

I like a thin mash, around batch volume, with a small sparge to wash off the surface sugars. So split mash: sparge water 4:1 or 2:3
I leave malt pipe draining in a bucket, during boil, Adding the extra 0.5L or so produced, at 10min boil time.

 

[Bobby_M]

One mod that I have made to the Brewzilla and other AIO units is to install a whirlpool return specifically for stirring the heated area and forcing more integration of the area you're talking about. In the Brewzilla and Vevor, since they feed the pump via bottom drain, I did it through the existing side mounted accessory drain. It's a pretty simple/cheap mod that does make a noticeable difference.

 

[hungupdown]

The best way would be to split the wort return between inside and outside the pipe, with the wort being returned below the surface of the liquid. For the outside return, you want to angle it to get a mild whirlpool action to be sure that all of the wort outside the pipe gets well mixed. You would also want a floating mash cap both on the inside of the pipe (circular) and outside of the pipe (annular ring.)



Depends a lot on the specific details of each method. Not sure that a blanket statement is possible.



Yes, keeping the bottom of the malt pipe (and any perforated portion of the pipe) just under the surface of the wort during the lift should minimize O2 exposure during a lift & lower. However, lifting the pipe will suck air into the grain bed to backfill the space vacated by the wort.

Brew on

Not sure that outer recirculation needs to get so complicated. Since I started the idea, back in 2023, I've never had efficiency issues.

I use the original recirc hose running at full flow, angled through a lift hole at 45° to help a spinning flow.
The base temperature sensor in the g4 35L, is about opposite the sparge arm. So I position the malt basket, so the angled flow can be aimed towards the sensor (to reduce base overshoots, even though using the BT probe sensor).

But even if pipe was dead vertical. The convection currents, from lighter liquid on one side moving round. to replace denser liquid on the other side that's decending, would cause gradual mixing.



Lifting the malt pipe means the grain bed is no longer floating. This puts a huge extra weight on the base of the grain bed, particularly high with the BZ tall narrow profile. This can cause grain bed compaction, leading to a stuck mash.

If you must lift. Lift very slowly, so wort height in the malt pipe never rises much above that around it.
A fast lift, means the grain bed is supporting nearly the full mash water plus grain weight. That's the same effect you get when malt bed recirculation is too fast, causing level in malt pipe to rise, while the surrounding level falls.

 

[mashdar]

Not sure that outer recirculation needs to get so complicated. Since I started the idea, back in 2023, I've never had efficiency issues.

I use the original recirc hose running at full flow, angled through a lift hole at 45° to help a spinning flow.
The base temperature sensor in the g4 35L, is about opposite the sparge arm. So I position the malt basket, so the angled flow can be aimed towards the sensor (to reduce base overshoots, even though using the BT probe sensor).

But even if pipe was dead vertical. The convection currents, from lighter liquid on one side moving round. to replace denser liquid on the other side that's decending, would cause gradual mixing.



Lifting the malt pipe means the grain bed is no longer floating. This puts a huge extra weight on the base of the grain bed, particularly high with the BZ tall narrow profile. This can cause grain bed compaction, leading to a stuck mash.

If you must lift. Lift very slowly, so wort height in the malt pipe never rises much above that around it.
A fast lift, means the grain bed is supporting nearly the full mash water plus grain weight. That's the same effect you get when malt bed recirculation is too fast, causing level in malt pipe to rise, while the surrounding level falls.

Do you have recirc through your mash? It sounds like you're just making a very nice heated jacket, but I may be missing something.

edit: To elaborate on what Doug said above, water more than a few inches from active recirc is surprisingly happy to sit stagnant.

 

[doug293cz]

Not sure that outer recirculation needs to get so complicated. Since I started the idea, back in 2023, I've never had efficiency issues.

I use the original recirc hose running at full flow, angled through a lift hole at 45° to help a spinning flow.
The base temperature sensor in the g4 35L, is about opposite the sparge arm. So I position the malt basket, so the angled flow can be aimed towards the sensor (to reduce base overshoots, even though using the BT probe sensor).

But even if pipe was dead vertical. The convection currents, from lighter liquid on one side moving round. to replace denser liquid on the other side that's decending, would cause gradual mixing.



Lifting the malt pipe means the grain bed is no longer floating. This puts a huge extra weight on the base of the grain bed, particularly high with the BZ tall narrow profile. This can cause grain bed compaction, leading to a stuck mash.

If you must lift. Lift very slowly, so wort height in the malt pipe never rises much above that around it.
A fast lift, means the grain bed is supporting nearly the full mash water plus grain weight. That's the same effect you get when malt bed recirculation is too fast, causing level in malt pipe to rise, while the surrounding level falls.

My post you quoted is specifically about how to do things if you are trying to go LoDO. If you aren't worried about hot side O2 exposure, things can be simpler, as you say.

Brew on

 

[kohalajohn]

One mod that I have made to the Brewzilla and other AIO units is to install a whirlpool return specifically for stirring the heated area and forcing more integration of the area you're talking about. In the Brewzilla and Vevor, since they feed the pump via bottom drain, I did it through the existing side mounted accessory drain. It's a pretty simple/cheap mod that does make a noticeable difference.

Bobby,

Tell me a bit more about that. You draw off from the low, side mounted accessory drain. Do you run a hose from there, outside and up and over the top and then poking into the pipe lift hole?

I can see there are many ways to do this. That is, if you're into recreational plumbing. I was thinking about putting a Y in the sparge hose itself and creating a whirlpool return that way.

 

[hungupdown]

Yeah, and speaking of oxygen, the method of shoving the recirc hose into the pipe lifting holes, means you are introducing a lot of oxygen. The hole is of course above the level of the wort, so it is spraying against the outer wall and then splashing down the empty space before hitting the wort. It would introduce more oxygen than the lift and lower method

Lifting exposes the whole grain surface area to the oxygen sucked in as the wort's drained.

Oxygen solubility in water, and the maximum dissolved amount, reduces with temperature,
Tap water generally has oxygen levels around 6-8 mg/L.
At 65°C (149°F) it's about 3mg/L.

If oxygen is 3mg/L after heating to mash temperature, you can't make more dissolve with any hose or spray, unless you first cool it.
You could, if the level started at near 0mg/L, after a pre-mash boil. But then why would you want to go lifting the malt pipe?

An exBeeriment comparsion of a LODO Kölsch, from the same beer made with higher amounts of oxygen, found tasters were capable of reliably distinguishing the two. And of those that did, 15 preferred the beer under normal conditions, 5 liked the LODO beer more, while 3 had no preference.

https://brulosophy.com/2017/04/10/t...ow-oxygen-brewing-method-exbeeriment-results/

 

[hungupdown]

My post you quoted is specifically about how to do things if you are trying to go LoDO. If you aren't worried about hot side O2 exposure, things can be simpler, as you say.

Brew on

My g4 is the 35L, where the lift hole centre is 4cm above the 30L mark.
Preferring a fairly thin mash, my mash water + grain generally reaches around 28L. So the standird recirc hose can easily reach down to (outer) wort level if LODO needed.

 

[kevin58]

The Anvil Foundry units have the same dead space issue and the solution users use is to lift the malt pipe a couple of times during the mash. I have experienced around a 8%+ increase in mash efficiency by doing this with both my Foundry 10.5 and 6.5

 

[doug293cz]

At end of mashing. The sugar density in the wort, can never be higher than of the liquid within the grain. But levels get closer the longer the mash, when sugars have more time to diffuse. Ideally they would become equal.

I think most brew in a bag brewers and batch spargers stir at the end of the mash in order to better homogenize all of the wort. A slow fly sparge also gives extra time for any sugar trapped in grits to diffuse into the wort. In other cases this might be a significant effect.

Using a grain absorbtion ratio of 0.8kg / litre. In say a 20L batch with 4kg grain, 3.2L will be absorbed. So a full volume mash would need 23.2L mash water, or 28.2L with 5L boil off. Giving mash water + grain volume = 30.22L
I suspect more wort is trapped, if you include that adhering between grain surfaces, but not sure if absorbtion figures factor that in (or if its after squeezing, or when left a few hours to drain).

If all the water was utilised during mashing, then on draining and getting 25L:
Fraction of wort left in grain = 3.2 ÷28.2 =11% Maximum ideal efficiency = 89%

When doing lauter efficiency calculations (which is what you are doing here) you need to base them on wort volume, which is higher than strike water volume due to the volume occupied by the dissolved extract. This makes the calculations a bit more involved than what you show. Working the the same grain weight and volumes (adjusted to 20°C) you used, and assuming a weighted grain potential of 80% dry basis (about 1.037) with 4% moisture, the calculation looks like this:

Dry weight of grain = 0.96 * 4 kg = 3.84 kg​

Max extract = 0.80 * 3.84 kg = 3.072 kg​

Weight of strike water = 0.9982 kg/L * 28.2 L = 28.15 kg​

Wort weight = 3.072 kg + 28.15 kg = 31.22 kg​

Max °P = 100°P * 3.072 kg / 31.22 kg = 9.84°P​

SG = 1.0393 (interpolated from 1918 Bureau of Standards tables)​

Volume of wort = 31.22 kg / (0.9982 kg/L * 1.0393) = 30.095 L​

​

Lauter efficiency = 100% * 25 L / 30.095 L = 83%​

​

The BZ g4 35 L, has a 14mm gap outside the malt pipe, with average gap circumference of (272+7)*3.142 = 877mm.
The 30L mark, is 340mm above top of the malt pipe perforations.
With 30.22L its about 342mm. So the dead water volume is: 342*14*877 = 4199076ml or 4.2L
Fraction of utilised wort in grain = 3.2 ÷(28.2-4.2) =13% Maximum ideal efficiency = 87%

The rigorous formula for the volume of the gap = height * pi * (R^2 - r^2) where R = vessel radius & r = pipe radius. But that only makes a difference between 4.2 & 4.3 L of dead water volume.

The total liquid volume is 30.095 L in the vessel at end of mash, and 4.3 L of that is water, so we have 30.095 - 4.3 = 25.8 L of wort. We collect 25 L of wort and water when we lauter, but again 4.3 L of that is "plain" water, so actual wort collected is 20.7 L, and we have:

Lauter efficiency = 100% * 20.7 L / 25.8 L = 80%​

The more rigorous math leads to the same conclusion as the previous math: the dead space water not being mixed well with the main wort has a much smaller effect on efficiency than anecdotal reports would lead us to believe. I was surprised by this result, and now we need another way to explain unexpectedly low efficiency seen by many brewers with AIO systems.

Brew on

 

[Bobby_M]

Bobby,

Tell me a bit more about that. You draw off from the low, side mounted accessory drain. Do you run a hose from there, outside and up and over the top and then poking into the pipe lift hole?

I can see there are many ways to do this. That is, if you're into recreational plumbing. I was thinking about putting a Y in the sparge hose itself and creating a whirlpool return that way.

No, I draw from the bottom drain, then split the pump output between both the top recirc and the side mound "drain" which actually becomes a whirlpool return instead. I'll see if I can find a picture. If not, I have a couple units I'm modding later this week.

 

[tracer bullet]

Us Anvil folks often use this in the bottom of the kettle, inside:

https://www.amazon.com/dp/B07G1B1YJM?ref_=ppx_hzsearch_conn_dt_b_fed_asin_title_4&th=1

Add a Wilser bag above it for your grain, and skip the pipe altogether. The bag will let the grain go all the way to the sides, and the grill grate will keep it off the bottom so there's somewhere for all that flow to go.

It not only eliminates that dead space (about 30% of the overall cross sectional area for the Anvil) it also means you've got a higher water-to-grain ratio making some mashes less "thick". No lift & lower and no LODO issues if you are chasing out them as well.

This is one I chalked up of a "AIO" a while back, discussing locations for temperature probes. Note an AIO is effectively "RIMS".

Indeed, it kind of led me to my AIO purchase. Wanted a RIMS for my cooler mashtun, looked into recirculation, started thinking how a coffee urn could be used, and eventually realized that's what an AIO was. With better temp control, and oh look we can skip the cooler and just put the grains right into the AIO.