Optimizing homemade ice cream freezing with brine

[couldabin]

This question involves a bit of background, so please be patient. I understand that the heat absorbed by ice's phase change from solid to liquid is much greater than the amount that results from the difference in temperature of the ice and the ice cream batter. So the primary cooling effect is from melting, not the initial temperature difference. We add salt to the ice because the freezing point of brine is lower than pure water, which "melts" the ice and absorbs heat. OK. So I'm thinking that putting rock salt onto ice cubes is a pretty inefficient way to create brine -- I always finds a lot of salt in the bottom of the bucket when I'm finished. My "solution" is to make a brine solution (1kg of salt to 1 gal. water) and put it in the freezer for two days, which lowers it to about 4F. I pour the brine into the bucket, and then adding ice. This has markedly reduced the freezing time, and this is where my question comes in. How much of this accelerated cooling is simply due to the temperature difference and total surface contact? Am I getting any benefit from melting, since the brine is colder than the ice? Would a higher brine temperature, say perhaps 25F, promote melting and therefore more rapid heat absorption? Any thoughts on how to calculate an optimal brine temperature (based on a known quantity of batter at a known temperature)? Thanks.

 

[anorlunda]

If it was me, optimum would be the best tasting ice cream, not the fastest freezing rate. Going slower means more mixing and that might have subtle effects on the flavor, so I would stick with the tried and true traditional methods. Especially if kids are involved, you don't want it to be all over in 10 seconds; the slower the freezing the more anticipation the kids feel.

BTW, the best home made ice cream I ever made used a generous scoop of pulp from a navel orange. Another great success used red and black currant berries.

 

[NTL2009]

If it was me, optimum would be the best tasting ice cream, not the fastest freezing rate. Going slower means more mixing and that might have subtle effects on the flavor, so I would stick with the tried and true traditional methods. ...

Yes, sometimes we let the technical "optimization" interfere with the optimum results we want to achieve.

Perhaps the OP wants to rephrase the question, and ask about the fastest way to freeze something? Or ask about how to make the best ice cream. They mmay not be the same thing.

But this makes me want to make some ice cream! I remember, I have four Madagascar vanilla beans left after using some to flavor a Vanilla-Oak-Stout I made, - should be just the thing for a nice Vanilla Ice cream!

 

[Littell]

Yeah, go with the best tasting.

 

[couldabin]

I do agree that the ultimate objective is the best-tasting ice cream. Turns out that the faster it freezes, the better the mouth feel. Liquid nitrogen produces magnificent homemade ice cream but it's not as practical as ice and rock salt. What I hoped someone could tell me is: how do I optimize the cooling effect? Does it involve brine rather than undissolved rock salt, as I assume? And if it does involve brine, how do I determine the ideal brine temperature?

 

[NTL2009]

This is a bit outside my field, but I think this is what you can focus on for the fastest freeze.

1) Get your cream and all ingredients and bowls/utensils as cold as practical (I understand now, we are trying to be practical here). So most of that could go in the freezer, the liquids maybe keep in a container in an ice bath so as not to freeze them solid.

2) Determine the optimal salt-water solution for the lowest freezing point. This info is easily found on the web. And though it isn't normally considered food-friendly, calcium chloride will get you to a lower temperature than sodium chloride (though I use calcium chloride as a mineral addition to some of my beers made with RO water, ~ 1-2 Tbs to five gallons). Careful, it can 'burn' your skin.

3) Use ice chips or shavings, or the smallest (most surface area) sized ice that is practical. You've seen large ice molds in a punch bowl, they take hours to melt. You want the ice to melt quickly to absorb heat quickly. Ice that hasn't melted hasn't done it's job for you. You won't hit that exactly of course, but you want as much ice to melt as practical.

4) I'm not sure, but it might make sense to start with a higher salt %, so that as the ice melts you don't dilute it and start climbing back up the curve.

5) I'm not sure of the optimum brine to ice ratio. You want enough brine to stay liquid, you want the liquid in contact with your bowl (liquid will pull heat faster than air or ice).

6) To some extent, a copper bowl will conduct heat better than stainless steel, but stainless is typically thinner in a bowl, and this may or may not be a limiting factor - it's thin and lots of surface area either way.

7) You will want to keep both the brine and the cream moving, to break up the barrier layers that will form, and keep conducting heat out of the cream.

I keep thinking of things... :)

8) A bowl (hemisphere) reduces surface area. You eant to maximize surface area. Maybe a copper shallow tray set in the brine (be careful not to get brine in the cream!

Here you go - Calcium Chloride @ 31% gets to ~ -50 C (!)
Sodium Chloride @ ~ 22% gets to ~ -21 C.

http://www.phasediagram.dk/binary/calcium_chloride.htm
http://www.phasediagram.dk/binary/sodium_chloride.htm

 

[couldabin]

Yes, thanks for this. It's very much along the lines I have been thinking. What is your thought on chilling the brine solution before it is put into the bucket? If ice cubes that are say, 15F are immersed in a brine solution that is 8F, will they melt?

 

[NTL2009]

Yes, I think so. Let's use C, it's easier, even for me, raised on F.

Say we held some ice cubes in a compartment at ~ -1 C (just below freezing) until they stabilized all the way through, and did the same thing with a brine. Say the brine has a freezing point. of -10 C (but it is at ~ -1 C now).

As I understand it, if we add the ice, the temperature of the brine will be pulled near it's freezing point of - 10 C (below that of either the brine or the ice), by the melting of the ice. Hopefully, someone will correct me on that if it is wrong.

But having the brine as cold as possible can only help, I think. It may not make much difference compared to the effect of the phase change absorbing heat, but I don't see how it can hurt.

Thinking in terms of the tray I explained earlier - if you poured a thin drizzle of cream on that tray (with ice/brine in contact with it on the back side), it should freeze super-fast. Scrape it, put it in a cold bowl, and pour another thin drizzle. Repeat as fast as it can be quick frozen. Might be easy for small amounts.

 

[couldabin]

Thanks for the observations. I guess I'll keep chilling the brine ...
:)