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When is Boiling not really Boiling?


bdevidal
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As an offshoot of the To cover or not to cover thread, as well as my chicken stock post, I was thinking...

When is boiling not boiling? If you are boiling (or simmering) to drive off water or concentrate something, you are really doing two things: you are removing water and applying heat. Normally it would follow that one is a direct result of the other. But what if you separate them? Heat, depending on its degree, does more than boil off the water. It breaks down chemical bonds, creates new compounds and flavors, etc. For example, take Fat Guy's example of simmering an uncovered tomato sauce to reduce it and concentrate the flavor. What if instead of applying heat to boil the water (and all the other things heat necessarily does), we removed the pressure? Air pressure at sea level is a little over 14 psi. If we were to drop that pressure down to a little less than a half a pound per square inch, well within the capability of even most cheap vacuum pumps, the water would boil at room temperature. You could concentrate/reduce the sauce without any of the heat effects. You could also vary up and down the scale by simply controlling the vacuum. I have a large pressure canner that I'm sure would hold that kind of vacuum (with a couple of modifications). I'm trying to imagine what you could do with a technique like this that you can't do right now.

Anyone have any ideas?

-B

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I think I read somewhere that a "reverse pressure cooker" has already been developed and is already in use in at least a couple of commercial kitchens.

Dropping the psi so that water "boils" at low temperatures allows the food to come out the other end essentially raw but having picked up lots of flavor along the way from everything else that was in that pot.

I can think of a couple of things I'd like to do with this, but currently both involve fish and meats and serving everything raw just for the curiosity factor.

If you are interested in trying this, post your endeavors and your results (hopefully with photos).

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Thanks for the intriguing post.

Yet another reason why this web site should have a Food Science discussion area.

SSB's of the world, Unite! :laugh:

 

“Peter: Oh my god, Brian, there's a message in my Alphabits. It says, 'Oooooo.'

Brian: Peter, those are Cheerios.”

– From Fox TV’s “Family Guy”

 

Tim Oliver

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Intriguing indeed.

Few questions come to mind:

It seems to me that for any kind of reduction or concentration to take place, vapor would have to be removed from the cooking vessel, necessitating continuous pumping. How would that affect the level of vacuum in the cooking container?

Also, how would you deal with evaporative cooling of the vessel and contents? Increasing vacuum levels to sustain a boil would cool the contents even further requiring higher vacuum levels and so on until the contents freeze or the container implodes. Or would you introduce heat to the vessel?

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The thing you're looking for is a gastrovac.  You can buy one at Le Sanctuaire.

Edit: Here is a link to it.

Interesting. I'm fairly certain a DIY version with greater capacity could be made for under 300 bucks or less (much less if you already have a pressure cooker or a vacuum pump). I have no idea how they can charge 3800 dollars for that unless it's just a really tiny market.

-B

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Interesting. I'm fairly certain a DIY version with greater capacity could be made for under 300 bucks or less (much less if you already have a pressure cooker or a vacuum pump). I have no idea how they can charge 3800 dollars for that unless it's just a really tiny market.

You can build yourself an immersion circulator for a couple of bucks also when the real thing is a grand or more. It's a tiny market, the product works, and the product is targeted at restaurant kitchens where building and maintaining some hacked together solution isn't worth the effort.

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Intriguing indeed.

Few questions come to mind:

It seems to me that for any kind of reduction or concentration to take place, vapor would have to be removed from the cooking vessel, necessitating continuous pumping. How would that affect the level of vacuum in the cooking container?

Also, how would you deal with evaporative cooling of the vessel and contents? Increasing vacuum levels to sustain a boil would cool the contents even further requiring higher vacuum levels and so on until the contents freeze or the container implodes. Or would you introduce heat to the vessel?

Vapor removal has a couple of options. Most pumps are rated in how many CFMs they can move, so I believe that as long as the vapor volume was less than the pumping volume you could establish any vacuum you want. Also, if the vapor volume exceeded the pumping volume, the vacuum would decrease (pressure would increase), the liquid would stop boiling, less vapor would be produced, and the vacuum would increase; I assume it would naturally tend toward equilibrium. Of course, that doesn't address the issue of actually running that water vapor through the vacuum pump, which I assume is not good for it and would immediately re-condense as it hit atmospheric pressure. You would have to set it up like a still, with a boiling chamber and a condensing chamber (ice water) prior to the pump. In fact, part of what got me thinking about this was a discussion on vacuum distillation as a way of reducing the energy input needed to produce ethanol. In practice, you would prob want a desiccant filter between the condenser and the pump just to make sure you're running as little water vapor through the pump as possible.

The cooling issue is interesting. In practice, you would want to have some controllable means of introducing heat so that you could control the process all the way up to boiling @ STP (or at least pressure). Stove would work, a PID controller would prob work better. You could do without external heat if you controlled how hard of a vacuum the pump pulled. The pump would vacuum, the liquid would boil (assuming a boiling point below room temp), the liquid would cool to the point that it stopped boiling, the pump would stop at the preset vacuum, the liquid would absorb heat from the surrounding vessel, which would in turn pull heat from the room temp air, the liquid would warm to the point of boiling again, repeat. Now in this case, without knowing how the temp gradient would be distributed in the vessel or the liquid, I'm unsure if it would reach an equilibrium or would oscillate up and down. Plus it would take forever.

Have you seen the new (somewhat) design for self cooling beverage cans? They use a two part lower section separate from the beverage. The upper half of the lower section is in contact with the bottom of the beverage portion and is filled with a water gel. The bottom half of the lower section is a vacuum with a solid desiccant. Somehow (still not sure) when you activate the cooling unit the barrier between the two cooling sections is breached, the vacuum+desiccant causes the water in the gel to boil, drawing heat from the beverage and cooling the drink.

Still trying to think of some other uses for the above rig...

-B

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Interesting. I'm fairly certain a DIY version with greater capacity could be made for under 300 bucks or less (much less if you already have a pressure cooker or a vacuum pump). I have no idea how they can charge 3800 dollars for that unless it's just a really tiny market.

You can build yourself an immersion circulator for a couple of bucks also when the real thing is a grand or more. It's a tiny market, the product works, and the product is targeted at restaurant kitchens where building and maintaining some hacked together solution isn't worth the effort.

I'm amazed at how often that's the case in many different and divergent circumstances. And in some (most?) cases, the hacked/DIY version is as good or better than the commercial equivalent. There's a great tutorial on doing home pressure bagging of composite laminates (like high quality fiberglass mat or carbon fiber) using a vacuum pump based on an old refridgerator compressor. I've been thinking of making my own electric convection oven with all sorts of custom goodies (lower and higher heat range that commercial, integrated rotisserie, larger capacity, boosted infrared for broiling, PID control, etc) and even with those add-ons it would be still be pretty cheap. Of course, such an oven wouldn't and shouldn't be used installed in a kitchen like a normal, UL-listed oven. But that's why there is the great outdoors...

-B

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Increasing vacuum levels to sustain a boil would cool the contents even further requiring higher vacuum levels and so on until the contents freeze or the container implodes.

One other thing: That's pretty much (as far as I know) how freeze drying works. They freeze the material, then put it in a refrigerated vacuum chamber. The material stays below freezing, but the low vacuum drastically increases sublimation. When it's done, you're left with a fine dry powder. It's also similar to how they make dry ice. It's cost prohibitive to either generate a cold enough or high enough pressure environment to make CO2 solid, so they compress the CO2 to a liquid state, let the heat of compression dissipate, then suddenly drop the pressure. A portion of the liquid CO2 boils off rapidly, dropping the temp of the rest of the CO2 and producing little solid flakes of frozen CO2. This is then compressed into blocks of dry ice. It's amazing that that process is even remotely economic enough that you can run down to the local grocery store and buy a block for a couple of bucks.

-B

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Right, so doesn't that just mean what everyone already knows?  If your time has no value then it's almost always cheaper to design and build your own solution. This guy keeps trying to build a nuclear reactor in his back yard...

I would disagree with the "no value" part. There are plenty of things that are hard to come by for any price, regardless of pay grade. If all I need is a blender that does what a blender does, I'll go buy a blender. If I need a blender that does something very specific for which there is limited or no market, then DIY it is going to have to be, short of paying someone else to build it for you. And what's the fun in that? :biggrin:

The other thing is that, other than personal or monitary benifits, DIYing things (within reason) often provides insights into and solutions for other problems. Or it may spur some new creative idea that hasn't been conceived of before. Or maybe it's just because taking stuff apart is fun.

-B

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I would disagree with the "no value" part. There are plenty of things that are hard to come by for any price, regardless of pay grade. If all I need is a blender that does what a blender does, I'll go buy a blender. If I need a blender that does something very specific for which there is limited or no market, then DIY it is going to have to be, short of paying someone else to build it for you. And what's the fun in that?  :biggrin:

The other thing is that, other than personal or monitary benifits, DIYing things (within reason) often provides insights into and solutions for other problems. Or it may spur some new creative idea that hasn't been conceived of before. Or maybe it's just because taking stuff apart is fun.

Hey, you're preaching to the choir. I drive a British car, I built my own coffee roaster, cold smoker, greenhouse, etc... I'm with you on the ridiculous project thing, but where you lost me is bitching about the price for an NSF certified product that is designed for restaurant kitchens.

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I would disagree with the "no value" part. There are plenty of things that are hard to come by for any price, regardless of pay grade. If all I need is a blender that does what a blender does, I'll go buy a blender. If I need a blender that does something very specific for which there is limited or no market, then DIY it is going to have to be, short of paying someone else to build it for you. And what's the fun in that?  :biggrin:

The other thing is that, other than personal or monitary benifits, DIYing things (within reason) often provides insights into and solutions for other problems. Or it may spur some new creative idea that hasn't been conceived of before. Or maybe it's just because taking stuff apart is fun.

Hey, you're preaching to the choir. I drive a British car, I built my own coffee roaster, cold smoker, greenhouse, etc... I'm with you on the ridiculous project thing, but where you lost me is bitching about the price for an NSF certified product that is designed for restaurant kitchens.

Ah, gotcha. That prob came across as more gripe'y than I intended. I completely understand why a pro-product would cost as much as they do, what with design requirements, insurance concerns, etc. It was just a personal off the cuff remark reflecting my own finances more than anything; there was a moment of "Man, you know how much gear I could buy for 3800 bucks..."

What do you drive, MGB? Sprite? Sunbeam?

-B

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Ah, gotcha. That prob came across as more gripe'y than I intended. I completely understand why a pro-product would cost as much as they do, what with design requirements, insurance concerns, etc. It was just a personal off the cuff remark reflecting my own finances more than anything; there was a moment of "Man, you know how much gear I could buy for 3800 bucks..."

What do you drive, MGB? Sprite? Sunbeam?

I'm not buying a gastrovac for $3800, but then again I don't think I'd spend $300 on one either. It's just not the sort of thing that appeals to me. The build it yourself thing really appeals to me, but this particular problem isn't one I've got any need to solve.

I used to drive a triumph spitfire until two of the wheels nearly came off. Now I've got an Elise - it's a much more livable British car, assuming you don't try and parallel park (no bumpers).

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