How did New Englanders make applejack?
In New England people used to make a strong drink from cider called applejack, but I heard they didn't do it by distillation, but by some sort of freezing. How does this work?
Distillation is a common way to make strong alcoholic drinks. The alcohol evaporates faster than the water and can be captured and condensed to make a stronger alcoholic beverage. But there is indeed another route, using ice instead of fire.
If you have a mixture of alcohol and water and it starts to freeze, you'll get ice on the top. Since water freezes at a higher temperature than alcohol does, the ice will consist mostly of water.
Similarly, if you put fermented cider out on a cold night and take the ice off the top in the morning, the liquid left behind will have a higher concentration of alcohol.
Since alcohol lowers the freezing point of water (think of antifreeze), you need quite cold winter nights for this. I imagine that early New Englanders were glad to find some use for those coldest of times.
You can see a similar effect, with colored substances standing in for alcohol, if you put a glass of orange juice in your freezer. The ice on top will be much less orange than the juice below.
This process, fractional crystallization, is an important technique chemists use in the lab.
You could also think of this as a way to purify water (the ice is made of purer water than it came from), and a rather similar process is used to purify silicon for the electronics industry.
Dr. Knowledge is written by Northeastern University physicist John Swain. E-mail him at drknowledge@globe.com or write to Dr. Knowledge, c/o The Boston Globe, PO Box 55819, Boston, MA 02205-5819. 