Melting Point of an Ethanol/Water Mixture

Factual Questions
1

I’ve been storing spirits (40% ABV) in the freezer and they’ve always remained liquid at that temperature. Recently, in my naive understanding, I placed a bottle of vermouth (18% ABV) in there and was surprised to find the next day all I had was a bottle of hard slush. This got me thinking: at what proportion of alcohol will that solution not freeze at typical freezer temperatures?

In my dim memory of chemistry, I remember that a mixture of two miscible compounds will have a melting point (freezing point) lower than the melting point of each compound individually, with a sharp depression at the eutectic point. Is there anywhere to find an ethanol-water melting point curve?

I suppose for the purposes of this question, we might first consider a solution of pure ethanol and water without impurities, but we could also consider the effects of the various other compounds typically found in alcoholic beverages.

2

Ideal freezer temperature is variously quoted at 0˚F or -20˚C. This corresponds to roughly 32% - 33% alcohol. Here’s a rough table: Ethanol Freeze Protected Water Solutions

3

A quick search turns up this:

18% ABV freezes well before 40% ABV, so it’s not surprising. You really need quite a bit of ethanol – about 93-94%, judging from that picture – to get the eutectic point. -20C corresponds to about 30% alcohol, as Nametag said

4

Aha! “Phase diagram”–the term I couldn’t think of. Thanks, Cal!