News from Richard Bleil
At the grocery store recently, I saw some pre-made in-store meatballs that looked just fabulous. My family has a recipe for a marinara sauce that I just love, but always makes too much since I’m alone. The extra I put into freezer bags for later. While my recipe is meat based, it does not have meatballs per se. It’s more of a sauce, making it excellent for recipes like Chicken Marinara and Lasagna (I make amazing lasagna). So, I think you see where I’m going with this, Meatballs Marinara.
But when I went to grab the leftover spaghetti sauce, I found it was nearly thawed. Yes, indeed, my refrigerator died. I guess I can’t complain. I moved into this house ten months ago and needed to buy a washer and dryer and replace the stove. But I was fortunate that, as beat up and dirty as it was, the refrigerator seemed to work fine. Until two days ago.
So, off I go to buy a new one. Now, this old one has built in ice and water dispensers, but I don’t have water access on that side of the kitchen. I do have gas, though, so now every time somebody goes for ice the freezer farts. I always blame the cat. I went to a major home repair store hoping beyond hope that they keep space on their trucks specifically for refrigerators so people like me won’t lose food. Of course, they don’t. The earliest delivery was two days out (tomorrow as of the writing of this post, a little less than a week on the day it should post). Which leaves an interesting problem.
My friend on my social media page insists that a freezer, if left unopened, will keep food cold for up to four hours. Well, we’re already well beyond that. But I am a chemist, and better than that, a thermodynamicist. Surely, I can solve this problem.
Of course, the answer is simple. I should point out that regular ice won’t do it. Everything in the freezer, with the exception of ice itself, is a solution of some sort. Let’s take ice cream as an example. Ice cream is mostly water (from the milk), but also contains fats, sugars, and many other items added to the milk or, frankly, as part of the milk itself. There is a colligative property called “Freezing Point Depression” that tells us that solutions, like ice cream, always have a lower melting point than the pure solvent. In other words, if we put big blocks of regular ice in the freezer, it’ll equilibrate at a temperature around 32oF, the freezing point of water, and everything will melt anyway (albeit slightly slower). Nope, we need to drop the temperature to well below the freezing point of water.
Most freezers are set to 0oF, or a full 32 degrees below the freezing point of water. While it might not be possible to get the temperature that low with materials easily obtainable, I still would like the temperature to be below the freezing point of water. Enter dry ice.
Dry ice is solid carbon dioxide. It’s considered “dry” because it does not go through the melting stage of becoming liquid, but rather, it “sublimes”, meaning it converts from the solid form directly to a gas. Just as water has a melting point, dry ice has a sublimation temperature, specifically -109oF. This is far below the set temperature of most freezers, but it’s unlikely that it will get the entire freezer that specific temperature.
See, the insulation of a typical freezer is good, but not that good. It could be better, plus we have all of the food in the freezer as well, which will need to re-freeze. Here’s a concept that will blow the minds of some readers; every time something goes to a more condensed state, it releases heat. That is, is water freezes, going from liquid to solid, it releases heat. This sounds counter-intuitive since it freezes at a temperature that we consider cold but think of it this way. We put ice in our drinks to keep them cold, because as ice melts, it absorbs heat. If melting absorbs heat, it’s reasonable that the opposite action, freezing, will have the opposite effect, namely releasing heat. It’s the job of the freezer to absorb this excess released heat during the transition.
So as my thawed, or partially thawed, food refreezes, it will release heat which will be absorbed by the dry ice. Simple thermodynamics says that heat is conserved so if it’s lost in one location is has to go somewhere else. I have a digital meat thermometer, but I wasn’t sure if it would work at sub-freezing temperatures. Fortunately, it does. So, I unplugged the refrigerator (if it’s not cooling, then the motor is doing nothing but generating heat), dropped about 20 pounds of dry ice in the freezer, and set up the meat thermometer.
And, yes, it worked. The temperature stabilized at around 14oF not as cold as a running freezer but cold enough to freeze the food inside and lasted for about a full day. As of the writing of this, I put another 30 pounds in it, which should hold until tomorrow afternoon when my new freezer is delivered. If not, I can get a little more dry ice in the morning.
If you use this trick, be very careful if you’ve never handled dry ice before. It can easily cause frostbite or skin burns if mishandled. Always use gloves, and never touch the dry ice as the moisture on your skin will freeze more or less instantly on it causing the dry ice to stick to your skin, damaging it as you struggle to remove it.
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