Wort Chilling - New Idea

Howdy everyone,

I had this crazy idea this morning about a new method to possibly chill beer faster than IC coils.

Vacuum Chilling, hear me out on this one.

Every time you use a pressure cooker you heat the water above its normal boiling point due to above normal atmospheric pressure inside the vessel.

If you remove the pressure regulator a violent boil occurs as the water is de-pressurized. The temperature drops rapidly between 126oC (15bar) to 100 oC.

What if you were to develop a way to reduce the pressure of the boil kettle below ambient?

at 0.5 psi water boils at roughly 80F
4 psi at 150F
8 at 180F

maybe a heavy duty shop vac could be used to drop the pressure?
you would probably still need the IC but this could be an interesting way to drop below 150F rapidly.

Cheers,
Matthew

Makes me think of a Little Feat tune.

".........pass it over to meeeeeee.............."

A heavy duty shop vac wouldn't pullenough of a vacuum to affect the temp. You'd have to have a serious air pump. And you'd have to have a boil kettle quite a bit larger because your wort will expand as you pull the air out of the vessel. Not to mention a kettle designed for negative pressure.


Be easier to use dry ice. cools down stupid fast and produces CO2 as a by product.

The temp drops because energy is used to convert the liquid to a gas. If you pull a vacuum on the wort, you are going to generate a lot of steam.

It would be fairly easy to try out. Just get you an old fridge and use the compressor off of it. That is a positive displacement pump and will pull a fair vacuum. Make you a lid from a few layers of 1/4 lexan glued together. Most kitchen pots will handle a few psi of negative pressure.

Hartski said:

And you'd have to have a boil kettle quite a bit larger because your wort will expand as you pull the air out of the vessel.

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Not really. I wouldn't think. Water is a non compressible fluid, so in theory there would be no expansion of the wort due to the pressure drop. I think there should be a contraction of the wort due to the evaporation and the drop in temperature.

Water might be a non compressable fluid, but wort is a bunch of stuff in suspension in said fluid. i don't know how it would react in a vacuum.

I would want to be observing this experiment from a good distance.............

Maybe I'm not thinking about this right, but wouldn't decreasing the pressure in the vessel make the hot wort (just under 212F) boil at lower and lower temperatures (as you increase vacuum), which would make a more and more violent boil inside, producing a ton of steam, which, without a way to release its pressure (due to the vacuum), would just build pressure again? And if you did release all the steam, wouldn't it just be a ton of extra boil off? Or would the steam created from the violent boil (at lower than 212F) not raise the pressure again?

I guess the real question would be, possible or not, whether or not it would really be any faster than an IC, which is pretty darn fast, particularly from 212F down to the 180F or whatever we are talking about for the realistic vacuums you might achieve in kitchen pots. The initial cooling from the IC is really pretty quick.

In any event, I can't imagine that the setup this would take to really work would be worth the effort compared to a CFC?

I do look forward to hearing more about it from someone with a better physics mind than me :fro:

^I was wondering the same thing. messing with pressure either positive or negative and hot liquids usually ends badly....

Let's say, theoretically, that you have a boil vessel that's capable of holding pressure, and an effective means of creating at least a partial vacuum in the boil vessel.

It's been a long time since I studied physics, so bear with me...

So, high pressure = high boiling temp. Therefore, low pressure (i.e. partial vacuum) should equal lower boiling temp.

So, take the kettle off the heat source, it starts cooling from 212° (+/-) naturally. You don't chill it at all, it's going to pretty quickly cool down to ~200° just based on the ambient temperature.

Now, you reduce the pressure, what's going to happen?

The wort's just going to start boiling again, isn't it? How's the energy actually being removed in this equation? Where's the energy going?

Maybe if you've reduced the wort's boiling point to 150°, that's all well and good, maybe the wort's boiling at a lower temp - but what happens when you release the vacuum and the wort's now at normal atmospheric pressures?

I can understand how changing the pressure would impact the boiling point, but I fail to see how this does anything to remove the energy that's stored in the boiled wort.

Not that any of this is in any way, shape, or form feasible. Even if you don't like immersion chillers, a $100 pump and a $100 40-plate wort chiller is going to be hard to beat in terms of cost and efficiency.

The much more *interesting* question, in my mind... if you COULD build a vacuum-capable wort boiler, wouldn't you be looking to do your BOIL at a reduced temperature? Pretty sure that's how malt extract is made. "Vacuum boiling," not "vacuum chilling."

the_bird said:

Now, you reduce the pressure, what's going to happen? The wort's just going to start boiling again, isn't it? How's the energy actually being removed in this equation? Where's the energy going?

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Into boiling. Water "resists" going above 212F normally because even when you add energy, that energy goes into boiling liquid into gas instead of heating up the liquid. That's called "heat of vaporization." When you decrease the pressure so that the liquid is above its boiling point, it boils very rapidly and gives up that heat quickly.

Maybe if you've reduced the wort's boiling point to 150°, that's all well and good, maybe the wort's boiling at a lower temp - but what happens when you release the vacuum and the wort's now at normal atmospheric pressures?

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The wort stops boiling immediately, and just sits there.

The much more *interesting* question, in my mind... if you COULD build a vacuum-capable wort boiler, wouldn't you be looking to do your BOIL at a reduced temperature? Pretty sure that's how malt extract is made. "Vacuum boiling," not "vacuum chilling."

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Well, you still have to get the temperatures high enough to do all the "good stuff" you do in the boil (hop isomerization etc.) So you can't reduce it too far.

Hartski said:

Water might be a non compressable fluid, but wort is a bunch of stuff in suspension in said fluid. i don't know how it would react in a vacuum.

I would want to be observing this experiment from a good distance.............

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the compressibility of water is on the order of ~4.4e-10/Pa. That's all I got, I rarely know enough about something to post in these forums, but I know that!

billvon said:

Into boiling. Water "resists" going above 212F normally because even when you add energy, that energy goes into boiling liquid into gas instead of heating up the liquid. That's called "heat of vaporization." When you decrease the pressure so that the liquid is above its boiling point, it boils very rapidly and gives up that heat quickly.

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Still... where's that heat going? It can't dissipate into the atmosphere, you've got to have a closed system or you aren't going to be creating a vacuum. Once that water vapor boils off, it's going to build up pressure in the headspace, isn't it, defeating the purpose of creating the vacuum in the first place?

What am I missing? How is this not circular?

the_bird said:

Still... where's that heat going?

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It goes into creating steam. Steam requires a lot of energy to form and gives up a lot of energy when it condenses.

It can't dissipate into the atmosphere, you've got to have a closed system or you aren't going to be creating a vacuum.

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You can't have a closed system! You have to constantly be pumping the air (and steam) out of the vessel. Otherwise the pressure just rises until the new pressure moves the boiling point higher again, and the boil stops.

(You could do something really fancy, like having a 40F heat exchanger somewhere else to condense out the steam into a separate container, in which case you could keep the pressure lower by condensing out all the steam. That would give you a more closed system. But you'd still end up with all that extra water on the cold side.)

That's the part I was having trouble wrapping my head around, it wasn't just creating a vacuum, it was creating and maintaining one. Can't imagine any scenario in which this would be remotely feasible as a cooling mechanism, not when the conventional solutions are pretty straightforward, low-cost, and relatively efficient.

So it sounds like even if this did "work" to cool the wort, you would lose a ton of it to steam.

okay, so at least a few of us with better minds than mine are having issues with the concept. I feel better now.

I may have to get a "rice pot" and pull 30 mm of mercury on it , and see what temp I get it to boil...... lucilky I have access to that kinda toys...

No. As already stated, that is simply the temperature at which water turns to vapor. by doing such, yes, the temp would decrease because there would be less molecular collisions. However
a) a shop vac certainly won't do it
b) when applying pressure to bring it back to ambient it would heat up again.

In essence, with extremely heavy duty (read millions of dollars in expense) equipment it would work, but only until you returned pressure.

The reason a pressure cooker cools so rapidly is the same reason a can of compressed air gets cold after you use it. A gas (or any substance) at one volume, can also exist at a lower temperature at a larger volume or lower pressure. The actual formula (Ideal gas law) is P_0*V_0/T_0 = P_1*T_1/V_1

If you pull a vacuum on the wort, any decrease in temperature will be met with an equal increase in temperature when the pressure returns to ambient.

This isn't to say you are totally off track here. There's a Mythbusters episode where they cool a 6 pack of beer in 5 seconds using fire extinguisher discharge. Also the same concept with how fridge's and AC units work. I'd be curious how much a fire extinguisher can cool 5gal of 200F wort

It would work if you could keep the vacuum on it, the heat would rapidly go into creating the steam. When you let off the vacuum you'd have the wort at whatever the temp it was at, minus the boiling. If you could get it down to about 1/2 PSI you'd be at ~70-80 *F so you'd be close enough to fully cooled, but good luck getting it that low

http://www.engineeringtoolbox.com/boiling-point-water-d_926.html

cockybitz said:

b) when applying pressure to bring it back to ambient it would heat up again.

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Nope. The air in the system would get a bit warmer due to Boyle's Law, but since wort is incompressible it would not change temperature. It would remain at the new (lower) temp.

billvon said:

Nope. The air in the system would get a bit warmer due to Boyle's Law, but since wort is incompressible it would not change temperature. It would remain at the new (lower) temp.

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This is correct. All the heat went into evaporating the water, which was then pulled out of the system by the vacuum pump.

Severe back of the envelope calculations say that to cool 20l of wort from 100 C to 20 C requires removing 6694.6 kJ of energy from the system... which would be the heat of evaporation of about 3 kg of water... which would be about 3700 liters of water vapor at STP that the vacuum pump would have to pull out of the vessel.

This was not accounting for the change in heat of vaporization at lower temps, so is, as I said, severe back of the envelope, but it would take a pretty healthy vacuum pump to do it in any sort of real time.

Also, good luck finding a reasonably priced brewpot that could handle the negative pressures without catastrophically failing.

Better spending less money on 1/2" Tubing IC with a recirculated cooling fluid solution that goes through an acetone-dry ice bath chiller...

Or any one of a dozen other options...

A couple of people are on the right track with this one. First, when something boils (essentially water here), it just means that its temperature is at the point where the vapor pressure is equal to the pressure of the environment (inside of pot). If you put a partial vacuum on this system, the boiling point will decrease. Assume you start at room temp, ~70° F and begin to remove air. As your pressure decreases, you begin to approach the point where the liquid will boil at this temperature.

One big problem is being able to accomplish the things you need to accomplish during a boil at this temperature, like alpha acid isomerization and microorganism destruction. I imagine the latter might happen, but not so much the first. The reason I'm guessing is that you need the temperature (which is a measure of thermal energy) for the isomerization. Temperature may be vital to these reactions.

If you are looking to boil at atmospheric pressure and then use some device like this to cool the wort, what are you really doing according to thermodynamics? Removing heat. Anything you're talking about here doesn't actually remove heat.

Bmorebrew said:

If you are looking to boil at atmospheric pressure and then use some device like this to cool the wort, what are you really doing according to thermodynamics? Removing heat. Anything you're talking about here doesn't actually remove heat.

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Nope, you're missing the point.

The idea is to pull a vacuum and cause the wort to boil because evaporating water cools the water that remains... the pump pulling out the water vapor cools the wort. The evaporation and removal of a portion of the wort removes heat from the system.

This was an idea to cool the wort through evaporative cooling post-boil, not to replace the normal boil.

It isn't a good idea from a cost/energy standpoint, but in theory, it would work.

I appreciate the thinking outside the box but for what a pump that can pull a vaccuum that strong and can handle lord knows what temperatures will be involved would cost you could run a couple or few therminators with a good pump wide open and run ice water through them and have 30F wort in your fermentor at 2-3 gallons a minute. Higher performance, lower cost, similar overkill.

Well, yeah, was this ever anything more than a theoretical exercise? Couple hundred bucks, you've got a big-ass plate chiller and a March pump, pumping out pitching-temp wort as fast as you can pump it. Have to believe it would be a LOT more efficient, too; not much energy used in getting your chill water, if you use an efficient enough chiller you won't waste THAT much water, and a pump can't draw too much juice (hell, pump's really optional, you *could* use gravity).

remilard said:

I appreciate the thinking outside the box but for what a pump that can pull a vaccuum that strong and can handle lord knows what temperatures will be involved would cost you could run a couple or few therminators with a good pump wide open and run ice water through them and have 30F wort in your fermentor at 2-3 gallons a minute. Higher performance, lower cost, similar overkill.

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Not saying this is a viable idea, but...

As I said very early in the thread, a fridge compressor would do it just fine. The temp is not a huge issue. Just leave a fairly long piece of hose between the pot and the pump. The water vapor would be more damaging than the temps.

I'm still confused on the number of people worried about the pot collapsing? Sure, pots aren't designed to see pressure, but they can handle a pretty fair amount. A cylinder is a pretty efficient shape for dealing with force.

We use the exact setup I talked about on page 1 all the time. 4 layers of 1/4" lexan bonded together as a lid over the mixer bowl of a 30 quart hobart mixer. Threaded a fitting through the lexan and have an old compressor out of a chest freezer pulling a vacuum on it. I've never put a gauge on it to know how strong it is, but it is doing it's job just fine. The lexan bows down about 3/4" in the middle of the bowl, but the bowl itself doesn't even begin to deform.

Vacuum equipment is extremely expensive, just FYI. I work with a lot of MDC products and just a flange is on the order of $250. Pumps (diaphragm, turbo, cryo) are all REALLY expensive and diaphragm pumps are the only ones capable of pumping out anything above 1 ATM without self destructing. Ask me how I know a cryo pump while turn into a giant block of ice if exposed to atmosphere... oops...

I don't have a thermodynamics book in front of me, but how much vacuum are we talking about? You may not need anything that I mentioned...

Seems to be a lot of interest in the physics of the idea,

I agree the equipment costs would most likely be absurd in relation to the cost. and if you couldn't generate enough of a vacuum it would definitely not beet out IC.

I still wouldn't mind trying the experiment out. I have an old sankey keg sitting around that I think my shop vac hose could be attached to. might fill it half with water at its boiling point and see what happens (behind a wall or something)

I'll post any results.

Cheers,
Matthew

Huff360 said:

I'm still confused on the number of people worried about the pot collapsing? Sure, pots aren't designed to see pressure, but they can handle a pretty fair amount. A cylinder is a pretty efficient shape for dealing with force.

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The vapor pressure of water at 20 C is 17.5 mmHg... .023 atm... while not a huge vacuum, a lightweight pot would be under considerable force leading toward collapse.

Several years ago I knew an engineer that tried to do an altitude test on the cheap by pulling about a 5 psi vacuum on a 55 gallon steel drum and the drum started to fold inward on him...

PorterIdontknowher said:

Several years ago I knew an engineer that tried to do an altitude test on the cheap by pulling about a 5 psi vacuum on a 55 gallon steel drum and the drum started to fold inward on him...

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I'll get some pics of my setup. Guess I need to find a vacuum gauge. Or maybe a long skinny piece of clear pipe. I've been looking for something to do with that bottle of mercury in the shop!

Huff360 said:

I'll get some pics of my setup. Guess I need to find a vacuum gauge. Or maybe a long skinny piece of clear pipe. I've been looking for something to do with that bottle of mercury in the shop!

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Those Hobart mixing bowls are really hefty, so I wouldn't doubt that you can pull a considerable vacuum on them. I'm looking forward to your results and some pics!

Hartski said:

Be easier to use dry ice. cools down stupid fast and produces CO2 as a by product.

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I have not heard this before. Not to get off topic from the OP but do you just put the dry ice directly in the wort? If so, how much for a 5 gallon batch?

PorterIdontknowher said:

The vapor pressure of water at 20 C is 17.5 mmHg... .023 atm... while not a huge vacuum, a lightweight pot would be under considerable force leading toward collapse.

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Indeed. Take a Boilermaker 15gal pot. At .023atm absolute pressure inside, there would be 2800 pounds pushing on the bottom of the pot alone.

Pulling a vacuum on hot wort would do a couple of things..

It would cause the wort to boil easier, at reduced pressure. The process of "boiling" under reduced pressure is endothermic, ie: heat is absorbed. If there is no longer a heat source, the temp WILL drop as the pressure is reduced further until the vapor pressure of the wort is equal to the reduced pressure from the vacuum. Cooling will ONLY occur during this period where the vapor pressure of the hot wort is higher than the reduction of pressure from the applied vacuum. It is the process of "boiling" under reduced pressure that causes the loss of heat.

This WILL chill the wort, but it will also generate a lot of water vapor (steam) that will either go through the vacuum pump (if it's a diaphragm pump) or it will get absorbed by the pump oil (if using a high-vac pump). If a high-vac pump is used, a cold-trap should be employed to condense out the water vapor as it will reduce pump efficiecy if absorbed into the oil.

It's an interesting idea, but honestly, it sounds like a lot of work for very little pay-off. Vacuum pumps are expensive, and one would need to have a boiling kettle that is vacuum tight. I don't think a pressure cooker would work, as they are designed to handle positive pressure, not reduced pressure. You would also need a lot of head space to handle the foaming/boiling of the wort as pressure is reduced. In the lab, we call this "bumping" and things can get out of control quickly if there is no internal agitation (like stirring with a stir plate).

Dry ice would be an option, as someone mentioned. I would be a little concerned about localized freezing of the wort. If the kettle is in contact with dry ice, it could potentially freeze it against the sides of the kettle if there is no internal stirring. Dry ice is really cold (-78C or -110F), so it could be possible to accidentally freeze the wort in contact with the sides of the kettle. stirring during the cooling process would be the only way to avoid this.

I work as a bench organic chemist, so I do have experience with this kind of stuff...
marz

billvon said:

Indeed. Take a Boilermaker 15gal pot. At .023atm absolute pressure inside, there would be 2800 pounds pushing on the bottom of the pot alone.

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The risk of implosion on a kettle is not an issue in this situation. The wort would all have to boil away before the kettle would implode, as the liquid will always vaporize before an implosion event could occur.

If you're going to use compressors to cool the wort, why not just use refrigeration to cool the wort? Just send chilled water thru your wort chiller.

conpewter said:

Those Hobart mixing bowls are really hefty, so I wouldn't doubt that you can pull a considerable vacuum on them. I'm looking forward to your results and some pics!

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Oh, I'm not trying to cool wort with it... I was just taking about the ease of getting a 'good enough' vacuum pump from an old freezer (yes I know, this is not a lab grade, cryo grade, refrigeration grade vacuum. It was just a suggestion so that if the op wanted to test the idea, he could cheaply get a pump.) The bowl I have is also no longer food safe. It's mixed lots of stuff that don't need eatin!



It pulls about 27 inches of mercury. We use it for degassing experimental composite rocket propellant.

Cheap and dirty, but it's worked for several months now. If it ever kills over, we'll trash it and get another from the local appliance shop. Nothing to it.

I wonder if you could send the hot wort to space for a quick chill in vacuum and it is really cold in space too.

wow... that is one ghetto looking vacuum pump! experimental rocket propellant, ehh? I like your style. You would approve of my pnuematic potato gun/flaming barbie doll launcher... too bad it exploded in my face last summer. cheap ass PVC.