Instant Ice Packs

[FoggyScope]

Ive got a bad idea help me out.

Has anyone used instant cold packs (smush the bag, shake and get cold) as a stop gap to cool meat long enough to get to town to buy ice?
I live in montana and weekend warrior most of hunting season. I mostly do 2 to 4 day trips a few hours from home. I hate filling a cooler with ice to dump it out 3 or 4 days later. Plus sometimes getting ice is tricky at 4am on the way to somewhere if i didnt have much time thursday or friday night.
My idea is to keep like 50 of them in the cooler in the back of the truck when I go out. If i get an animal Id do my best to cool the meat in the field before the hike out. Then at the truck break the cold packs and put the meat in and drive the hour or so back to the nearest town to refill with real ice to get the few hours home.
Im sure this isnt cheap or as good as ice its more about laziness and having one less thing to deal with when taking off for a weekend where i might or might not fill a tag. If i dont, its there for next weekend.
I know i could have a chest freezer full of milk jugs of ice but then i have to have another freezer in the garage so im trying to avoid that.
Anyone tried something like this?

 

[taskswap]

The important detail isn't that they get cold, per se. It's the BTUs of heat they can absorb. If you put an ice cube in a pot of boiling water it will lower the temp, but probably not even stop the boil. 20 ice cubes will bring it down enough to actually feel cool to the touch. The ice cubes are all the same temp, it's just that 20 ice cubes "absorb" a lot more heat than 1 can.

These packs usually only last 20-30 minutes and aren't very big. My intuition is that this could be a heavy (they still contain water and ammonium nitrate or similar, plus their 10mil plastic bags...), expensive, inefficient alternative to something cheap and effective.

If you want to know for sure, this is easier to measure than find on line. Just go get one or two. Get a pot of water of a known quantity (say, a gallon) and measure its starting temp (let's say it was tap water and is 50F). A BTU is the amount of heat required to raise 1lb of water 1 degree F, and it works in reverse - lowering it 1 degree F meant something "absorbed" 1 BTU of heat. Activate a pack and put it in the water for 15 minute or so, then measure the water temp again.

BTU = WaterQty (Lbs) * dT (degF). If you had a gallon of water (water weighs 8.34lbs/gal) and lowered its temp say 3 degrees, the math would be BTU = 8.34 * 3 or just about 25 BTU.

Once you know this you can work the math all kinds of ways. Google says the heat density of meat is about 0.8 BTU / lb so if you have 200lbs of meat in two coolers, and want to lower its temp from, say, 80F (let's say it cools a bit while you pack it out) to something safe (let's say 40F or better) you need to remove (200*.8) * (80-40) or 6400 BTU of heat - minimum. If one ice pack removes 25 BTU, you'd need 256 ice packs to get the job done. Meat isn't much safer at 60 than 80, so if you're going to do the job you may as well do it right.

Now my numbers are all guesses. My intuition tells me this isn't going to be cost-effective. But you can do the experiment above to find out. A 50 pack of instant cold packs on Amazon is about $33 right now. If you needed 250+ packs that'd be $165 in ice packs just by the math above. But say in the experiment you find it lowers the temp by 15 degrees instead of 3 - win! Then you'd only need (at least) $33 worth of ice packs.

Personally, I think I'll stick with ice. But it's fun to think it through.

 

[butcherboy]

There’s no reason to do this. Cool the meat out overnight. Pack it out. Drive to town for ice. You can hang it in the mountains for a few days in the shade just fine. No shade? Make an A-frame game pole with a tarp over it for shade. It’s never a bad idea to have an extra freezer in your garage either. I also use ice sticks I’ve made from 2” and 3” pvc. Cut to fit your coolers and glue an end cap on. The other end glue on a threaded collar. Fill with water leaving a small gap on top for expansion and screw the cap on and freeze. Drain them when you get home and store dry in a cardboard box.