Help with freezing water/salt mix...and chemists out there?

[Mike Goetzke]

Homebrewing is one of other hobbies. My son recently gifted me a plastic conical for fermenting my brews. It's called FastFerment if you want to see one. I bought the optional insulated jacket to see if I could chill it enough to brew lagers. You cool the liquid down by hanging 2L bottles of ice inside the jacket.

I've gotten it to cool somewhat but nowhere near the performance the web site says. I added a small fan inside the jacket and bought an Inkbird temperature controller and it vastly improved the performance but I could get to 49F with 64F ambient. Some say they get 20F from ambient without the fan.

They say to add salt to the water before freezing to enhance the cooling power but don't really say how much. Online I did find some links where people add salt to water in bottles to use in their chest coolers. I found a few references saying to use 1 cup/gallon.

I put 1/2 cup rock salt into the 2L bottles and put them in the freezer. They are not totally frozen now. Did I use too much salt? Or is this how it should be? Is it best to add just enough and still get a totally frozen bottle?


Thanks,

Mike

[Shawn Pixley]

Salt in water lowers the freezing point. When frozen (matter in a solid state) it will equalize to the ambiant temperature. That is if you freeze at -20 F (plain water or salted water) it will be -20. But pure liquid water will only get to 32 (absent some special conditions).

I don't know that system as I lager in a refrigerator. It sounds however that you want the coldest liquid possible to maximize heat transfer (cooling a jacket around you wort). Adding salt can allow you to have a liquid at well below 32 degrees as you have found. I would try it as you have it now.

[Malcolm McLeod]

I'm not a brewer or a chemist, but have had Thermodynamics class, made ice cream, and chilled one or a thousand beer cans.

I am not quite following your setup with the 2L bottles and the jacket system, but I think Shawn is on the right track. - - Salt dissolved in water lowers it's freezing point. So if you mix salt with water it might not freeze in your refrigerator/freezer (typically the freezer section is at ~30degF). You might get it to freeze solid in a chest freezer (typ. at ~0 to 5 degF).

I think you'll have better luck if you approach it like ice cream making. I'll probably not get the details just right, but the result should be close. Mix ice, a little water, and rock salt in your cooling jacket. The water and ice mixture is considered a 'phase change' and will be at 32degF. The salt begins to dissolve, and by going into solution absorbs a LOT of energy. The energy has to come from somewhere - and in this case it's from the water. So, the water cools below 32 degF but doesn't freeze. Since it's still liquid, it can still circulate around your wort vessel and absorb energy from there.

Your heat transfer with water will be massive compared to air (people are just cool in 45 degree air; they die of hypothermia in 45 degree water).

We always froze ice cream by using a 6:1 ratio of ice to salt (6 cups of ice to 1 cup of salt), until it was soft frozen and we pulled the dasher out. Then it was packed at 4:1 to freeze it hard.

[Alan Rutherford]

As Malcom says, it's the phase change, not the temperature that's important. Ice that starts at 20 degrees and is still frozen at 32 hasn't done as much for you as it will while it melts at 32. Thawing frozen salt water should give you about the same result as thawing unsalted water. Thawing crushed ice rapidly by mixing it with salt sucks up a lot of heat (i.e. produces cold) in a hurry.

[Tom Stenzel]

Like everyone mentioned above adding salt to water lowers the freezing point. So yes, you only want to add salt and still be able to freeze the salt water solid. It's the change from solid to liquid that absorbs the BTUs. What it won't do is increase the amount of BTUs that are absorbed in the melting. That is, the saline solution will melt faster as it's melting at a lower temperature, that causes the heat to transfer faster.

The plastic of the 2l bottle might be slowing the heat transfer too. Not sure what the solution (ahem!) to that would be.

Anyway a quick surf of the net trawled up the following. It's a direct lift from sciencing.com (errors and all):

******
Freezing Point of a Saline Solution

The freezing point of any saline solution depends upon the concentration of NaCl in water.

As an example, the freezing point of water is lowered by 1.85 degrees Celsius (38.33* degrees Fahrenheit) when 29.3 grams of salt is dissolved in each kg of water. This is a 0.5 molal solution of salt; molality is the amount of solute (expressed in moles) divided by the mass of solvent (expressed in kg), for mol/kg.
***********

*1.85 degrees C is equal to 3.33 degrees F. But everything on the net is true so I must be wrong.

Anything to help such a noble cause. Like making beer.

-Tom

[Matt Schroeder]

Following up on Alan's comment, while it is true that thawing water at 20 vs. 32 doesn't give much of a different result, the water starting at 20 and absorbing heat to get to 32 will give you more energy absorption than ice heating from 20 to 32 would. Ice has a heat capacity of about 2 J/gK while water is about 4 J/gK--so raising the same amount of water and ice from 20 to 32 deg will absorb twice as much energy for the water as the ice (and therefore help keep your system colder).

[John Stankus]

I'm a chemist...we can go into the thermodynamics of it all, but it might be better(and faster) to look at the wikipedia page on cooling baths. https://en.wikipedia.org/wiki/Cooling_bath

what temperature are you trying to maintain and how well regulated does it need to be?

John

the Methanol water dryice bath referenced in the wikipedia page might be the best way.
https://chemtips.wordpress.com/2015/02/23/the-ridiculously-thorough-guide-to-making-a-meohwater-bath/

[Jim Koepke]

what temperature are you trying to maintain and how well regulated does it need to be?

Don't forget how long?

Lager fermentation will take more than just a few hours. Unless brewing has changed a lot since my last batch.

jtk

[Mike Goetzke]

Thanks for all the excellent information. My fermenter is not in a bath it is hanging in space and the bottles are hung by cords below it. When I get home I will post some photos and additional information. From my experiment today, even though not all the water froze, the results are very promising. Ambient temperature was 66F and the fermenter started with 6-gallons of water at 64F. The water dropped by 10F so far in 6-1/2 hours. With pure ice water it was double this time. Lager's require fermentation of 45F-55F (but the wort warms up as it ferments).

I was wondering too if I add just the right amount of salt to still freeze all the water if this would be optimal - I'm using an upright freezer.


Mike

[John Stankus]

. Lager's require fermentation of 45F-55F (but the wort warms up as it ferments).




Mike

If its 45-55F you need. Just buy an old refrigerator. I'm not sure how big your fermenter is but a dorm/office size fridge is about $100.

John

[Mike Goetzke]

Here are some pictures of the conical fermenter with the ice bottles hanging.


This first pic is my grill wi-fi temperature controller that I use to monitor ambient and water temp from anywhere with internet access:

http://img.photobucket.com/albums/v212/mbg/Brewing/IMG_2220_zps50ssknho.jpg (http://smg.photobucket.com/user/mbg/media/Brewing/IMG_2220_zps50ssknho.jpg.html)




This is the insulated jacket:

http://img.photobucket.com/albums/v212/mbg/Brewing/IMG_2219_zpsscuy2ytt.jpg (http://smg.photobucket.com/user/mbg/media/Brewing/IMG_2219_zpsscuy2ytt.jpg.html)



and this is the way the bottles hang:

http://img.photobucket.com/albums/v212/mbg/Brewing/IMG_2218_zps0biuitrc.jpg (http://smg.photobucket.com/user/mbg/media/Brewing/IMG_2218_zps0biuitrc.jpg.html)



I'm looking to maintain 45-50F.


Mike

[Adam Herman]

air is a very poor conductor of heat, that is why insulation is just there to stop air from moving.

you will have a hard time getting any cooling at all with a fan blowing on some gallon jugs. you really need to have your cone contacting liquid.

[Ryan Mooney]

Also heat rises. If you can rig that setup up so the insulation is pulled in closer on the bottom and the cooling bits are set closer to the top you'll get a smidge more bang for your buck. You'll want enough space for there to be some air movement to move the heat/cold to the appropriate places (assuming non-direct contact as per below) but no extra wasted space.

I'm betting there is a measurable temperature differential between the top and bottom of your enclosure. You might get some small benefit from opening a vent at the top of the enclosure but I'm not sure, that's a trade off between venting heat and allowing in some ambient... I lack the tools to model that and would basically suggest to try it and see (wouldn't have to be very large I don't think).

Getting the cone in contact with the coolant more directly as Adam noted would definitely help more than anything else.. I suspect you could heat up some of the jugs a bit and deform them against a rough model of the cone so they would nestle in right next to it and rig up a holder to hold them in place fairly easily. Putting something between the cone and the jugs to increase heat transfer - like wet towels - would also help.

Its useful to think of thermal transfer as "moving heat" (this isn't really correct scientifically but it leads to more useful design thoughts) - basically the idea is that heat moves but cold doesn't so you want to figure out the best way to move the heat to the cold.

When I was in AZ I was able to get almost 20F of temperature drop by making a redneck beer swamp cooler. Basically I just put a t-shirt over the carboy, stuck it in a water bath and put a fan on it. Obviously that works best (only works) in places where the ambient humidity is in the high single to low double digits :) and I sure wasn't getting to lager temps but it did get me down into the low 70's so I could do some ales.

For amusement here is an interesting article on the predicted temperature rise (url mangled in the obvious ways to avoid the mods wrath) based on the OG of the wort.

http://homebrew dot stackexchange dot com/questions/5563/can-we-estimate-the-temperature-rise-in-the-primary-due-to-fermentation

That study was for the equivalent of an ale yeast, a significant percent of the exothermic reaction from yeast happens during the growth phase so if you're doing an appropriately large pitch of healthy lager yeast into a low/medium oxygen wort I would expect the curve to be somewhat lower although I'm not sure how much.

Alternatively you could just solve the problem once and for all :D :D
http://www.micromatic.com/glycol-cooled-components/power-packs
or DIY
https://byo.com/stories/issue/item/1877-build-your-own-glycol-fermenter

[Mike Goetzke]

Ryan - my son's fiance bought him a toy for brewing called BrewJacket. In this system a rod (I think aluminum) gets inserted into the fermenter to heat or cool the beer. It's $300.

Adam - I too think you need to have conduction to make this work. After much testing I'm thinking this is jacket I bought is good for ales and higher temp lagers. I have also found that it is good at maintaining temp once it has dropped. I even tried dropping an ice bottle inside the fermenter. I suppose if you sterilize it you could do this in practice to bring the temp down then maintain with hanging ice bottles.

I was really looking to find out if there was info on what the optimal ratio of water/salt to maintain 45-55.


Thanks

[Adam Herman]

Salt lowers the freezing point so that you can maintain the high conduction and heat capacity of a liquid vs. a solid. "to mantain 45 or 50" where? we have established that your setup wont really work well. the water/salt mixture will be well below 32 degrees.

[Mike Goetzke]

I contacted the company when I only got about 1/2 their performance and they sent me a replacement but still no change. I now thinking their claims are not possible:









http://img.photobucket.com/albums/v212/mbg/Brewing/Capture%20b_zpshcwe8oet.jpg (http://smg.photobucket.com/user/mbg/media/Brewing/Capture%20b_zpshcwe8oet.jpg.html)
http://img.photobucket.com/albums/v212/mbg/Brewing/Capture%20a_zpsjhecbe7l.jpg (http://smg.photobucket.com/user/mbg/media/Brewing/Capture%20a_zpsjhecbe7l.jpg.html)

[Lee Schierer]

Although pure water freezes at 0°C (32°F), water that has salt dissolved in it has to be colder before it freezes. If the water has as much salt dissolved in it as it can hold (that's called a saturated solution of salt), so that any further salt would just come out as crystals, the freezing temperature is around -21 °C, or about -6 °F. If your freezer isn't colder than that, the part of the ice touching the salt will start to melt. If you've put so much salt on the ice that the water can all melt and form a saturated solution, and still leave some salt crystals, then it will all melt. If you've put only a little salt on, it will melt some ice until the salt crystals are gone. Now as more ice melts the solution becomes less salty, more like pure water. So its freezing temperature goes up. At some point its freezing temperature will be the same as the freezer temperature, so the freezing will stop. You'll have some ice left, and some salty water.

If you are freezing your salt water solution in a refrigerator freezer, it is likely not reaching zero degrees F. Most dedicated freezers are set to zero degrees for food storage.

[Roger Feeley]

Mike, if it helps any, seawater freezes around 0 degrees Fahrenheit. In fact, Gabriel Fahrenheit established 0 degrees using the freezing point of the sea water around his Norway home. Then he took the difference between the freezing and boiling points of fresh water and divided it up into a convenient number of units (180). Using those two points for the degree unit, he came up with 32 degrees for the freezing point of fresh water. Add 180 to that and you get 212.

[Mike Goetzke]

Thanks for all the help. I have continued my testing because it doesn't take up too much time and it's been fun/interesting.

On my latest test:
- Have the water/salt ratio such that the 2L bottles freeze solid in my upright freezer.
- Determined 50F was about as low as I could go w/o changing bottles too often.
- Put an ice bottle inside the fermenter to get the water to desired temperature of 53F before adding frozen hanging bottles inside the insulated jacket.
- Used a small 12V computer cooling fan instead of the 10" 112VAC desk fan to circulate the air (in both cases used a temperature controller to turn the fan on/off).

I'm very pleased, using a wifi temperature device and the Inkbird temperature controller set at 53F +/- 1F I was able to control the water temperature to 53F +/- <1F for 41 hours with four 2L bottles in the jacket. It then rose to 54F and has stayed there for an additional 4 hours so far. So looks like I can go 2-days between ice changes (realizing fermenting beer temperature rises for the first few days I may need to change ice more often at the beginning).

Mike