More than meets the ice cream.

I hate it when my store-bought ice cream gets all icy in the freezer.  Unfortunately, the closest I've come to making my own ice cream was some fun with liquid nitrogen back in high school.  For those who are interested, it's actually quite easy, provided you have access to liquid nitrogen.  (Inappropriate use of lab resources, anyone?)

Remember those science experiments in high school where you made ice cream by churning cream over salted ice?  The goal was to demonstrate the phenomenon of freezing point depression when a solute is added to a liquid.  By adding salt to the water/ice mix, you lowered the freezing point of the ice to below the temperature it was currently at, causing it to start melting (the heat of solution of salt is negligible in this case).  In order to melt, though, the ice needs thermal energy, which it takes from the plastic baggie of cream and sugar you've got churning on top of it.  This causes your mixture to cool and become ice cream.  See (http://www.foodscience.uoguelph.ca/dairyedu/findsci.html) for an in-depth explanation.

Well, all that is fun and scientifically enlightening, but it takes an awful lot of work.  A faster method of cooling your ice cream solution would be to, well, use something really, really cold.  Just pour it in as you're stirring your mixture, and you'll have ice cream in minutes.  Since liquid nitrogen is so cold, the parts of your ice cream mixture that make contact will freeze very fast, which means the water doesn't have time to form into large ice crystals, which makes your ice cream exceptionally smooth.  Best of all, liquid nitrogen evaporates into, well, nitrogen, which can help aerate your ice cream as it boils off, and is completely harmless.  If only it was easier to get...

In the meantime, I am considering adding liquor to preserve the creaminess of ice cream.  Ethanol freezes at -114 degrees Celsius, which is quite a bit colder than your typical freezer.  Unfortunately, it makes sense to add the liquor while you're making the ice cream.  Still, there must be some decent way of adding it afterward.  Just pouring it in won't do, as the ice cream is too solid for the liquor to absorb.  Maybe if the ice cream was warmed to be on the verge of melting, then the liquor was poured in, mixed, and the entire mixture flash-frozen?  The difficult part would be flash-freezing the new mixture.  Nevertheless, it will have to be something to try out.