Five O'Clock Somewhere

Welcome to Five O'Clock Somewhere, where it doesn't matter what time zone you're in; it's five o'clock somewhere. We'll look at rural life, especially as it happens in Rio Arriba County, New Mexico, cats, sailing (particularly Etchells racing yachts), and bits of grammar and Victorian poetry.

Monday, August 08, 2005

Fresh-peach ice cream

Pat and I recently hosted an ice cream social to raise funds for our local community center. It was a great success, despite chilly, rainy weather that wasn't exactly great for ice cream consumption. It did, however, have one flaw compared to the ice cream socials I remember from the past -- all of the ice cream was store-bought. A true ice cream social would involve people coming together to share all different sorts of homemade ice cream.

I have particularly fond memories of my mother's family tradition -- fresh peach. In the summer, our family would go to visit my grandparents in a small town in Arkansas, and many aunts and uncles and cousins and inlaws and outlaws would converge. We'd go in Daddy Teague's pickup truck (for updates on the reconstruction of said truck, see Cousin Andrew's "Beer and Trucks" blog in the links list to the left) to a peach orchard just outside of town. Much of the orchard's produce was picked while still green, to be shipped to market elsewhere -- being unripe, and therefore firmer, meant the peaches wouldn't get bruised during shipping. However, there were always some peaches that the pickers missed until they were too ripe to ship, and these peaches were awesomely sweet, having ripened on the tree. So we'd get some of the very best peaches on Earth -- a key ingredient if you want to make the very best ice cream on Earth.

Next, we'd go to the ice house for a big, clear, 10-pound block of ice. The stuff sold in bags in the supermarket or convenience store would never do. The ice house was not the sort of place that in Texas is called an "ice house" -- in Texas, ice has generally become a secondary function, and cold beverages, especially beer, the primary reason for an ice house's existence. But in that county in Arkansas, Prohibition never ended; it's a dry county. So the ice house is actually about ice. Wow.

Once we got back to the house, Munzy would do something magical in the kitchen with the peaches, also involving cream, eggs, and sugar, and eventually she would come out with a rich, creamy mixture that was poured into the central cylinder of the ice-cream churn. The dasher (a complicated paddle that resembles a wooden Venetian blind) was inserted into the churn, the lid was placed over the cylinder, and cylinder was placed into the bucket, and the cranking mechanism was clamped over the top. Daddy Teague was a purist about the ice cream -- it wasn't really homemade unless the bucket was wood (preferably cedar) and the churn operated by a hand crank, not an electric motor.

Now the freezing process began. Daddy Teague would get out the ice pick and start chipping away at the big block of ice, filling the bucket around the cylinder. He would put in a layer of rock salt every now and then -- salt lowers the freezing temperature of water, so, even as the ice was melting into water, it was getting colder, to speed the process of freezing the ice cream.

The next hour or so would involve a lot of physical effort, but there were always plenty of cousins around to take a spell at the crank. We would crank the ice cream, and the cylinder in the middle would spin, and, unseen, the dasher inside the cylinder would spin in the opposite direction. As the cream mixture froze along the outer edges of the cylinder, the dasher would scrape it off the side to allow more cream to freeze, and the dasher would also whip air into the ice cream as it froze, to make it smoother. While cousins cranked, Daddy Teague would, as needed, chip off more ice to replace the meltoff that flowed out the overflow hole on the side of the bucket, and sprinkle in more rock salt to keep the freezing process going.

At the beginning, cranking would be easy, but as the ice cream froze, the crank would get harder and harder to turn. Gradually, the younger cousins would drop out of the cranking rotation, until at the end, only Uncle Warfield and Uncle Dupes were left to crank. When the ice cream finally got so firm that even they couldn't crank any more, that was the signal that it was time for the next step. (Ice cream churns with electric motors would have quit far earlier -- that's part of why hand-cranked ice cream is better than electric-cranked.)

No, the ice cream, even at that stage, was still not fully solid. The cranking mechanism was taken off the top of the churn, the dasher was removed and the lid replaced, a cork was used to stop up the hole in the top of the churn where the dasher shaft had been, the whole thing was packed with more ice and rock salt, and then it was left to set for a while, wrapped in a blanket to keep it cold.

Finally, an hour or two later, the ice cream had set up nicely. That was when we could enjoy the ice cream, and we could understand that it was so absolutely heavenly that it was worth all of the work. Yes, homemade ice cream is a huge lot of work. But there's nothing else like it.


Blogger Pat said...

Perhaps with the Heron Lake marina opening, we could set up a ice cream churn for Labor day weekend or some such.

Mon Aug 08, 12:14:00 PM MDT  
Anonymous Mom said...

Ice in bags did not exist at that time! It was not sold in grocery stores, only at the ice house, only in blocks!

Mon Aug 08, 03:39:00 PM MDT  
Blogger Carol Anne said...

By the time I was old enough to register memories, ice was available in bags at the grocery store, but still, that big block of ice was really pretty -- so crystal-clear, it was like glass. That big block of ice, and Daddy Teague chipping at it with the ice pick, was definitely part of the special ritual of homemade ice cream.

Mon Aug 08, 11:51:00 PM MDT  
Blogger Pat said...

Hmmm, my childhood memories of big blocks of ice were slightly different. They'd come from the ice plant -- which was fun to visit in the summer -- in a truck, in chunks about five feet tall, two feet wide, and about 10 inches thick. The truck would back up to a small loading load, where workers with tongs would slide the blocks about fifty feet to the crushing machine, which dispensed ice to crates of vegetables carried by the conveyer rollers. The crates would then be rolled onto freight cars or semi-trailers.

Tue Aug 09, 10:14:00 AM MDT  
Anonymous Jesse said...

Around here (and I suspect Texas too) people like to order Pat's giant blocks of ice and put them in their swimming pools on hot days.

As far as ice cream freezing better because salt water has a lower freezing temperature, that just didn't make sense to me. I had to do some googling, but I am correct. Actually I'm surprised your dad or brother didn't beat me to the punch. Water with salt in it does indeed have a lower temperature of freezing, but that is meaningless unless you are trying to make salty ice, and you have attached a refrigeration system to the ice cream bucket to remove heat. Instead, the salted water actually lowers its temperature chemically. Apparently, adding salt to the very cold meltwater causes an "endothermic" reaction as the salt splits into its sodium and chlorine ions on introduction to the water. The endothermic business absorbs heat, and thus lowers the temperature of the water/ice slush from 32F to whatever (depends on amount of salt among other things).

Wed Aug 10, 08:16:00 AM MDT  
Blogger Carol Anne said...

There's also the physics involved in the latent heat in the change of state from solid to liquid. When changing from solid ice to liquid water, H2O sucks up a whole lot of heat. That's why it only takes a few ice cubes to lower the temperature of tea from still-hot fresh brew to iced tea. I'd guess the latent heat of fusion is more important than any endothermic reaction. I believe most of the salt remains salt -- otherwise, we'd be generating some nasty toxic waste every time we make ice cream, especially since elemental sodium and chlorine are both seriously unstable. I don't have any physics textbooks ready to hand, so I can't look up the tables, but I'd guess it takes a whole lot of heat out of the ice cream just to convert 4 kilos of ice into liquid water.

Wed Aug 10, 11:38:00 PM MDT  
Blogger Carol Anne said...

Here's a way you can demonstrate the latent heat of fusion in your own home.

Brew up some tea. Then, while the tea is still so hot that it's steaming, pour it over ice. If your tea is at 95C, and your ice is at -5C (typical for a home freezer), if you put 500 ml of tea over 500 g of ice, then, you would expect to end up with one liter of tepid, weak tea at 45C. But that's not what happens. Because changing the state of the ice from a liquid into a solid absorbs energy from the tea, you get nice, cold tea, and you still have a good deal of unmelted ice floating in it.

Thu Aug 11, 02:34:00 AM MDT  
Anonymous jesse said...

Latent Heat of fusion is 3.3*10^5 Joules per kilogram. I wish we had the LH of fusion for other substances, because then we could have some perspective on just how huge the heat capacity of H2O is (and why retreating glaciers and ice packs are an alarming environmental development).

Thu Aug 11, 07:12:00 AM MDT  
Blogger Pat said...

A couple of search results...

We do know that salt water freezes at a lower temperature -- easily several degrees Fahrenheit -- than fresh water.

"When you are making ice cream, the temperature around the ice cream mixture needs to be lower than 32 F if you want the mixture to freeze. Salt mixed with ice creates a brine that has a temperature lower than 32 F. When you add salt to the ice water, you lower the melting temperature of the ice down to 0 F or so. The brine is so cold that it easily freezes the ice cream mixture. " (

Adding salt to the system will also disrupt the equilibrium. Consider replacing some of the water molecules with molecules of some other substance. The foreign molecules dissolve in the water, but do not pack easily into the array of molecules in the solid. Try hitting the "Add Solute" button in the animation above. Notice that there are fewer water molecules on the liquid side because the some of the water has been replaced by salt. The total number of waters captured by the ice per second goes down, so the rate of freezing goes down. The rate of melting is unchanged by the presence of the foreign material, so melting occurs faster than freezing.

That's why salt melts ice.

To re-establish equilibrium, you must cool the ice-saltwater mixture to below the usual melting point of water. For example, the freezing point of a 1 M NaCl solution is roughly -3.4°C. Solutions will always have such a freezing point depression. The higher the concentration of salt, the greater the freezing point depression [1].

But won't any foreign substance cause a freezing point depression, according to this model? Yes! For every mole of foreign particles dissolved in a kilogram of water, the freezing point goes down by roughly 1.7-1.9°C. Sugar, alcohol, or other salts will also lower the freezing point and melt the ice. Salt is used on roads and walkways because it is inexpensive and readily available.

The lowest temperature possible for liquid salt solution is -21.1°C. At that temperature, the salt begins to crystallize out of solution (as NaCl·2 H2O), along with the ice, until the solution completely freezes.

Why does water in a solution have a lower chemical potential than pure water? For an "ideal solution" (a solution in which all molecules interact in the same way) the chemical potential of water in the solution is given by

µsolution water = µpure water + RT ln xsolution water

where R is the gas law constant (8.314 J/mol K), T is the temperature, and xsolution water is the mole fraction of water in the solution. As salt is added to the water, the concentration of water in the solution goes down. That makes xsolution water less than one, and the natural log of a number less than one is negative. That makes the concentration correction negative, so the chemical potential of water will drop as more salt is added.

Fri Aug 12, 11:52:00 AM MDT  

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