Sorbets: A dash of liqueur and a sprinkle of SCIENCE!

A few recent experiments trying to make sorbets and icecreams without an icecream maker were reasonably successful, but suffered from a need for supervision. The frozen goodies had to be removed from the freezer and stirred/blended thoroughly several times to get a good texture, and still tended to become too hard for my tastes. I would probably have continued making them in this laborious fashion for some time to come, had I not been given a burst of inspiration by my partner. She suggested I make some sorbet using leftover ALDI apple schnapps as flavouring. Not only did this promise to be an exciting sorbet, but I realised it could solve all the problems of preparing sorbet without an icecream maker.

The purpose of all the stirring and blending of sorbets while freezing is to avoid large ice crystals, which turn smooth icecream into solid ice. Ideally, the finished product freezes only just enough to stop being liquid, without ever hardening fully. Most sorbets are at this ideal point straight out of the icecream maker or after a day or so of freezing. But even the best sorbet will often start hardening over the following days. By dropping the freezing point closer to a residential freezer's set temperature of -20°C, there is the potential to stop this from happening.

Ah ha! It's time for SCIENCE!

Alcohol freezes at a lower temperature than water. In fact, with a melting point of -114°C, it freezes at a lower temperature than carbon dioxide. DDBST has data for the freezing points of ethanol (non-poisonous alcohol) combined with water in different molar ratios. Some algebra (it's been a while, but I still remember the basics) produced a liquid-solid phase diagram for methanol and water with a more useful scale. Adding sugar affects the vapour pressure according to Raoult's Law, which further decreases the melting point and... sod it.

In the end, I made my usual sugar syrup, added schnapps until it tasted good and then tried freezing the results...

Twelve hours later, I gave it a quick stir to break up a few large ice crystals that had formed around the top, and put it back in the freezer. By this stage, my other sorbet would have already frozen through, but the liqueur sorbet was being more resistant and was still resolutely slushy.

Another twelve hours and it had hardened as much as it was likely to, forming a soft sorbet without a trace of sharp ice crystals. The method (splashing stuff in and seeing what happens) certainly needs some refinements in quantities, but the sacrifice (of making and eating sorbet) is one I am willing to make...

Next into the freezer: ALDI* triple sec orange sorbet.

* I'm not sponsored by ALDI, but I do like buying cheap liqueurs from them for my experiments.