I'm looking forward to our apricot tree having a goodly amount of fruit this summer. However, it's always more than we can eat at one time. I'd like to save some for year-round use.
In preparation for that, I've been experimenting with ways of freezing fruit. This weekend, I tried Alton Brown's method of using dry ice ("Good Eats", #602, 3-Jul-02, "Strawberry Sky"). His method has the advantage of quickly freezing a food so that ice crystals don't have time to grow large and rupture cells, rendering the food unpalatable when defrosted. He breaks the dry ice into small chunks and mixes it in a bowl with the food, leaving the bowl in a picnic cooler to keep the temperature low. It works, but it seems awfully wasteful of the dry ice because breaking it creates more surface area and it therefore sublimates much faster (and the cheapest dry ice I could find is $1.25 a pound, but then Alton is rich and deservedly so). You also have to fish the fruit out of a bowl of chunks of cold dry ice (hint - use gloves!). The method I came up with is a little different.
CAUTION -- Dry ice is really, really, REALLY cold. Touching it with bare fingers, even in its wrapper, could cause you some damage. Always wear gloves when handling dry ice, the thicker the better! And keep it away from kids!!!
Step 1: Picnic Cooler, Dry Ice, and a Pan.
I bought an 11-pound block of dry ice (sizes may differ; this was what they had on hand at the ice plant) and brought it home in a cooler. The dry ice comes in a plastic cover which I left on. At home, I put a half-sheet baking pan directly on top of it, and a sheet of parchment paper on the pan. The silicone-coated paper keeps the fruit from freezing to the metal.
Step 2: Fruit on the Pan.
We also have an orange tree which is ripe now. I started with about 25 pounds of oranges from our tree, much more than we could hope to consume at once. This picture shows my experiment with raspberries and melon slices from the market, but the orange slices worked much the same. Fill the pan with pieces of fruit so that each piece has as much contact as possible with the metal thru the paper. They can be packed much closer than you see here; I didn't have much of a problem with pieces freezing together. I wanted to try the oranges first because they're mostly all water.
Per Alton, DON'T latch the cooler shut if it has a latch because dry ice sublimates (ie. turns directly to a gas, CO2, and no one wants to be the historic first casualty of a cooler accident). Just keep the lid down.
It took between 30 to 40 minutes for the pieces to freeze solid. You can then (carefully!) lift the parchment paper with the now-frozen fruit on it. Don't touch the pan with your bare fingers! By now it's just about as cold as the dry ice! Each panful was then packaged with our vacuum food saver. This will stop moisture evaporating from the fruit and causing freezer burn. The very first picture shows a pack of the finished orange pieces, nice and plump after freezing.
To easily peel and separate the oranges, I used this method: http://lifehacker.com/dont-peel-oranges-quickly-u...
Step 3: Finished Product.
The raspberries and melon pieces froze well with almost no condensation. I wouldn't recommend this method for casual use; the dry ice is too expensive (two bucks a pound at the supermarket). However, if you have a freezer and large amount of food to preserve at once, like the output from a fruit tree or berry bushes, this works and justifies the cost. We got several bushels at once off our apricot tree in the past, which I believe we could easily freeze in a couple of days' work with this method. Yes, we could do jam preserves, but THAT would be a huge amount of one product and not necessarily a form that's useful in different ways. This way, apricot jam is still a possibility months after the peak harvest time, but then so are smoothies! Last thought -- I peeled and refrigerated the oranges first to get them as cold as possible before freezing them. It was easier for me to do one job at a time, peeling them all at once, then putting them in baggies for a couple of hours in the refrigerator to lower their temperature and make the freezing faster.
Finally, how long did the dry ice last? About 34 hours, from 11am on the first day to 9pm on the second day. The raspberries and melon pieces were frozen around 6pm on the second day, so the dry ice can still perform well even with smaller amounts. Next time, I'll put the dry ice on top of a thin piece of styrofoam in the bottom of the cooler as an additional insulator and see if that can help it to last longer.
All in all, I'd say this was worth the time to preserve a lot of our delicious oranges and apricots.