Wort Cooling Experiment

[Bribie G]

I was planning to get into BIAB after Christmas but decided to go early and get my kit together early December as an early prezzie to myself.

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basically a large cylindrical esky with tap and a large electric urn to use as HLT and boiler. I had a Bruheat in the UK and know this type of system works great - you can even buy dedicated cylindrical biab bags and sparge arm systems to fit a Bruheat and possibly adaptable to the urns you can get here so I might not even need the esky).
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Wort cooling: I brew to 24 litres in 30 litre fermenters. This gives me four or five useful litres of headspace and I have the following idea (probably not original)

Fill two 2L PET bottles with brine, fishing line loop around neck. Sterilise them externally, bag them in large freezer bags and freeze solid.

Unwrap, lower into fermenter and add wort from boiler/hopback. Fish out using the fishing line. Aerate wort with stone whatever..........


Now I last studied Chemistry and Physics around the time the Beatles were getting a few gigs ("who's the Beetles Poppie?" ) however I remember that the following needs to be taken into consideration:

Temperature that various strengths of brine can be frozen down to
Specific heat
Latent heat of freezing / melting

I can do a refresher but can anyone on the forum with a physics bent (Maybe Herr Doktor Butters for example) suggest what cooling effect 4 L of frozen brine could have? It occurs to me that if I had to go more than 5 or 6 L to get the effect then a bit of overgravity brewing might be necessary.

I should really get off my Ar$e and do a small scaler with a wee PET bottle but I would prefer to nail it down mathematically, maybe in a spreadsheet for future use and for general usage if anyone is interested.

 

[Phrak]

An interesting concept, if I understand it correctly.
Are you basically saying that you'll use a couple of big ice-blocks (albeit inside 2L PET bottles for easy removal) in the bottom of your fermentor to chill the hot wort straight out of the kettle?

I don't see any reason why it shouldn't work, provided you have enough "ice blocks" to cool to pitching temp.

 

[drsmurto]

Fill a 2L coke bottle with boiling water and see what happens to it.........

You will need to find a plastic bottle that is capable of withstanding >100degC otherwise you will damage the bottle and fill your beautiful wort with water.

From memory, the PET used to make juice containers is heat-set to prevent deformation and so can withstand a higher temperature.

 

[Bribie G]

Fill a 2L coke bottle with boiling water and see what happens to it.........

You will need to find a plastic bottle that is capable of withstanding >100degC otherwise you will damage the bottle and fill your beautiful wort with water.

From memory, the PET used to make juice containers is heat-set to prevent deformation and so can withstand a higher temperature.

hmmm.. sounds like some mat-lab testing is in order here before doing the thermodynamics calculations
Come to think of it, soft drink PETs are made as thin and light as possible so they can crank out the cola for a buck a bottle, but the juice containers are fairly rigid. Looking at my Cottees pine lime 2L right now and it's got lots of ribs and even has a 'cottees' embossed into it. And a handle I could use to fish it out with a sterilized hook. Thanks for the suggestion, Dr.
To the freezer I go and will report later Experiment one will be to pour a couple of jugs of boiling water over the frozen bottle and see what happens.

 

[buttersd70]

(Maybe Herr Doktor Butters for example) suggest what cooling effect 4 L of frozen brine could have? It occurs to me that if I had to go more than 5 or 6 L to get the effect then a bit of overgravity brewing might be necessary.

God, you like to make it hard, don't you.....

As Smurto said, though, the temperature effect on the pet bottles could well be an issue. But for calculation heat transferrence, the formula is

(h1*V1)+(h2*v2) / (v1+v2) =h3

where
h=heat
v=volume
1 and 2 referring to the coolant/wort, and h3 being the resulting temperature.

However, this is for water, not for brine (or wort for that matter), and (I believe) can only be used if the coolant and the liquid to be cooled are in the same energy state. (both liquid). It's also for high rate flow systems, where the T variable of time can be 'guestimated' if you don't want to use another formula (which I don't have to hand) not dunk and wait...then you would have fall off/rise in relation both to the wort temperature and the coolant temperature, which would add a variable into the equation that is beyond my ability to work out. You also have issues with surface areas, and the like.....

In short, it's just too hard to work out mathematically. One long formula with another long formula as one of the variables, and one of the variables in that formula relies on another formula....

 

[Haydo]

I dont think this is going to work unless I am misunderstanding what you are trying to do here...are you saying that you want to cool 24 litres or wort at 100 deg with 4 litres of brine to get it down to a temp you can pitch yeast?

If so, by my calcs you will need to get the brine to -400 degrees to get the wort below 30 degrees, thats colder than absolute zero!

 

[Bribie G]

Thanks, Butters, sounds like nailing jelly to the ceiling! I'm off to Woolies shortly so I'll get some very small PETs in the kids juices and soft drinks section and will put on my lab coat and do some scaled down runs, of course convincing the Mrs that I have finally lost my marbles (predicted when I bought my first fermenter) :lol:

While I've got you, with surface area of a cylinder such as a fermenter does the volume go up as a cube whilst the area goes up as a square or something like that? Thus affecting cooling time when doing a small system test? Maybe I should do the small scale run in an insulated container.

With dunk and wait I'd not be in too much of a hurry as long as the fermenter contents remain sterile.

 

[Trent]

Why not just get a bag or 2 of ice that has been made using sterile water and just dump that into yer fermenter? The main problem you will have with the bottles of ice in the hot water is that unless it is constantly agitated, the cooling effect will be close to zero, as it somehow insulates itself with a small layer of hot water around the outside or something similar. This is why convoluted CFWC are supposed to be better, and why I have to agitate the crap out of my post chiller (after the wort goes through my plate chiller, it goes through about 10m of coiled copper, immersed in an ice bath.) If I do not agitate the ice water, the wort receives almost zero cooling, and can come out at up to 30C. If I start to agitate it, withing 20 seconds, the wort is coming out at 16-18C.
I think there is alot of thermodynamics to think about, and Haydo has made a very good point about volume of brine required.
Its a good theory, not trying to shoot it down - just point out a possible weakness, but you will have to do alot of experimenting before you get it right.
Good luck with it
Trent

 

[Haydo]

Looking at your post again BribieG I realise now you are probably looking at removing the bottles when they "warm up" and putting some new frozen ones in there. You will still need a lot of bottles as as they "warm up" the rate of cooling of the wort will drop. I honestly think this would take hours, and you would probably be better putting your fermentor into the laundry sink, fill the sink with ice and keep stirring the wort to get the heat transfer happening replacing the ice as you go.

 

[buttersd70]

While I've got you, with surface area of a cylinder such as a fermenter does the volume go up as a cube whilst the area goes up as a square or something like that? Thus affecting cooling time when doing a small system test? Maybe I should do the small scale run in an insulated container.

Its the surface area of the bottles which are in contact with the wort that you have to look at, not of the surface area of the wort in the fermenter itself (altough there will be some cooling as a result of the surface area of the wort in the fermenter being in contact with ambient air).

Trent brought up a good point in relation to the wort 'insulating' itself around the cooling bottles. Basically, any temperature drop is affected by the difference in temperature between the 2 mediums, so once the temp of the wort in direct contact with the bottles starts to drop, the difference narrows, making the absorption of the heat less effective. The cooling effect will radiate out into the wort, but it is slow because the temp difference between the hot wort, and the slightly cooled wort is minimal. Hard to put into words, but if you consider the case of an imersion chiller of a large diameter. The larger surface area in contact with the wort, due to the larger circumferance, transfers heat, but if you consider it in cross section, end on, so its like you're looking at a circle, the water at the edge, near the pipe, transfers the heat, but it doesn't make it into the centre of the pipe, so the water in the middle is cool, if you know what I mean.....which is why an immersion chiller of a larger diameter has hardly any increase in efficiency than one with a smaller diameter, even though the surface area of the pipe is considerably larger....unless there is agitation of some sort, which allows the heat to radiate right through. And the same kind of issue would apply, I think, to a submerged bottle type setup.

I hope that makes sense, it makes more sense in my head than what I've written.

 

[RobboMC]

You can basically say as a rule of thumb that a kg of ice melting will cool one litre of water from 100 deg C to 0.
That's 100 deg.kg for the latent heat of melting people.

So you'll need 12.5 litres of brine to cool 23 litres wort to just 50 deg C,
and another 6.25 litres to get it from 50 to 25 deg C, so lets round it off to 19 litres.

Hence the invention of the chilling coil!

I cool about 3 to 4 litres of hot wort down to pitching temp with a 2 kg ice block, then add extract,
but I let it air cool a bit first as heat flows from the 99 deg C pot out into the 25 deg C air pretty quickly.

Using the latent heat of freezing of ice is a good idea, but it has it's limitations.
You may be better off with a 25 litre pail of ice and a heat transfer coil,
or a pail within a pail idea.

Also consider that heat flows better through metal, particularly copper and aluminium, so use a metal containers rather than plastic bottles.

PS Anyone ever thrown one of those plastic Esky freezer bottles into boiling water, they look pretty sturdy to me,
though if one ever cracks it's bye bye to the worty.

 

[Bribie G]

Thanks guys, that's certainly added a new dimension. I'll do some agitate / no agitate exeriments - I've sorted out a 3L jug that will be an excellent tenth-scale fermenter and get some 200ml PETs and see how they work, and how long they take to melt, then do a larger scale test with a 2L PET and see if I can come to any conclusions.

I've already visualised maybe a lot of little sterilized frozen PETs strung together and swimming in the wort then removed like reeling in a string of mackerel ... Brain meltdown brain meltdown :unsure:

I've lined up an English Best Bitter and a Scottish 80/- to assist my brain this afternoon and evening :icon_cheers:

 

[BusinessTime]

What if you brewed concentrated then added sterile/clean ice to dilute ?

 

[buttersd70]

Bear in mind that the agitation, in your case, will be in hot wort....with an immersion chiller, the 'agitation' isn't agitation as such, its whirlpooling.
Personally, I'm not a slave to the whole HSA debate, but in the case of the type of agitation required with immersed bottles, I'd be thinking about it....

Dare I suggest....No chill? Trying to be devils advocate and not wanting to start the whole debate chill-no chill, I would have thought that any (possible or percieved) risks associated with NC would be less than any (possible or percieved) risks with this particular method of chilling....

Just a thought.

 

[RobB]

What if you brewed concentrated then added sterile/clean ice to dilute ?

I have thought about this previously, but I think it would need to be a very concentrated wort to work. By my quick and dirty calculations, 13 litres of wort would need to be added to 9kg of ice.

My proposed method would be like a ******* son of no-chill. First put 9 litres of boiling water in a sanitised cube and seal the cube. Hopefully you now have 9kg of sterile water in a sterile environment. When the water has cooled the next day, freeze the cube (obviously this is going to require a fair bit of freezer space). At the end of your boil, drain 13 litres of hot wort onto the ice in the cube.

Now I know that the process is not going to happen in the neat steps below, but it should give a rough idea.

Latent heat of ice is 333 kJ/kg, so melting 9kg of ice takes 2997 kJ.

If all this melting energy is drawn from the hot wort and the specific heat of water is 4.18kJ/kg/K, then 13 litres of boiling water is reduced by 2997/(4.18*13) = 55 degrees.

So if you now have 9 litres of 0 degree water (the former ice) and 13 litres of 45 degree water (the cooled wort), they should mix to produce 22 litres at 26 degrees.

Now the equations for all these reactions occurring continuously, rather than in steps, would be far more complicated and are beyond me. These figures also don't give any indication how long all this would take.

One obvious concern would be the sudden temperature change in the cube. If it cracks, it would be a sad end to a brew day.

If anyone wants to test this out, be sure to post your results!

 

[PostModern]

What exactly is higher risk about no-chill compared to this "experiment"?

 

[RobB]

What exactly is higher risk about no-chill compared to this "experiment"?

Nothing, which is why I'm happy to no-chill and haven't ever bothered with testing my theory.

I just thought I would add some numbers to the discussion to demonstrate what might be required. That is, a couple of frozen PET bottles won't be up to the task of chilling a full batch.

 

[buttersd70]

What exactly is higher risk about no-chill compared to this "experiment"?

Nothing at all, PoMo....I said that NC would pose less risk than this experiment. NC has certain risks, which are calculated ones. As does rapid chilling. As does this. As does everything. I guess what I was trying to get at was that even NC detractors would possibly consider this method to be higher risk than NC, in the grand scheme of things. I'm not anti NC, not anti rapid chill, I've done both. I actually NC almost exclusively now. I was trying to be objective and avoid flaming from either side, or stirring up the whole argument. :unsure:

 

[PostModern]

Sorry, didn't mean to stir the pot. Just wondering about the benefit (if any) of going down this path, particularly in terms of energy and water consumption. Carry on.

 

[buttersd70]

Sorry, didn't mean to stir the pot. Just wondering about the benefit (if any) of going down this path, particularly in terms of energy and water consumption. Carry on.

No worries PoMo. Your wonderings are actually the same as mine.....just that mine are babbled, confusing, and easily missinterpreted. :lol: . We're actually on the same page.