Freeze Distillation
Freeze distillation is a term for a process of enriching a solution by partially freezing it and removing frozen material that is poorer in the dissolved material than is the liquid portion left behind. Such enrichment parallels enrichment by true distillation, where the evaporated and recondensed portion is richer than the liquid portion left behind.
Such enrichment by freezing of a solution in water is sometimes oversimplified by saying that, for instance, because of the difference in freezing points of water (0 °C/32 °F), and ethyl alcohol (-114 °C/-173 °F), "the water freezes into ice...while the ethyl alcohol remains liquid." This is false, and although some of the implications of that description are true and useful, other conclusions drawn from it would be false.
The detailed situation is the subject of thermodynamics, a subdivision of physics of importance to chemistry. Without resorting to mathematics, the following can be said for a mixture of water and alcohol:
- Freezing in this scenario begins at a temperature significantly below 0 °C.
- The first material to freeze is not the water, but a dilute solution of alcohol in water.
- The liquid left behind is richer in alcohol, and as a consequence, further freezing would take place at progressively lower temperatures. The frozen material, while always poorer in alcohol than the (increasingly rich) liquid, becomes progressively richer in alcohol.
- Further stages of removing frozen material and waiting for more freezing will come to naught once the liquid uniformly cools to the temperature of whatever is cooling it.
- If progressively colder temperatures are available,
- the frozen material will contain progressively larger concentrations of alcohol, and
- the fraction of the original alcohol removed with the solid material will increase.
- In practice, unless the removal of solid material carries away liquid, the degree of concentration will depend on the final temperature rather than on the number of cycles of removing solid material and chilling.
- Thermodynamics gives fair assurance, even without more information about alcohol and water than that they freely dissolve in each other, that
- even if temperatures somewhat below the freezing point of ethyl alcohol are achieved, there will still be alcohol and water mixed as a liquid, and
- at some still lower temperature, the remaining alcohol-and-water solution will freeze without an alcohol-poor solid being separable.
The best-known freeze-distilled beverages are applejack and ice beer. Ice wine is the result of a similar process, but in this case, the freezing happens before the fermentation, and thus it is sugar, not alcohol, that gets concentrated. For an in depth discussion of the physics and chemistry, see eutectic point.
Read more about this topic: Fractional Freezing
Famous quotes containing the words freeze and/or distillation:
“I sat at a table where were rich food and wine in abundance, and obsequious attendance, but sincerity and truth were not; and I went away hungry from the inhospitable board. The hospitality was as cold as the ices. I thought that there was no need of ice to freeze them.”
—Henry David Thoreau (1817–1862)
“In this century the writer has carried on a conversation with madness. We might almost say of the twentieth-century writer that he aspires to madness. Some have made it, of course, and they hold special places in our regard. To a writer, madness is a final distillation of self, a final editing down. It’s the drowning out of false voices.”
—Don Delillo (b. 1926)