Weird Ice balls in bottle

[Swimming_in_liquor]

Hey everyone 

I had something weird happen recently with some bottles of vodka we produce. 

A few friends have put some bottles of our vodka in their freezers and had some ice balls form in the bottle.

I’m quite certain I’m hitting 40% abv in the bottle and not dipping below it. Hitting 40-40.4% abv with density meter. 40% with hydrometer and temp correction. 

Volumes/weight of bulk tanks and number of bottles packaged are extremely close to bottling run calculations through out software. 

Any thoughts or ideas?

Could it be separating in the bottle?

[FIVE x 5 Consulting]

Per AlcoDens, freezing point of 80pf ethanol/water solution is -10 F.  Freezers are typically set to 0F.  It is not outside the realm of possibility that your vodka is hitting its freezing temp of -10F.

The other obvious possibility is that someone is stealing some vodka and replacing what they drink with water and returning the bottle, effectively dropping its proof and increasing its freezing point.  At 70pf, freezing point is only -2.3F

Final possibility, your gauging instrumentation is way off, although if you are getting matching readings with both hydrometer and density meter, this is not as likely

[meerkat]

The freezing temperatures given in AlcoDens are for well mixed solutions - as would be the case if the alcohol and water mixture was being pumped around a circuit and used as a very low temperature heat transfer fluid.  If the solution is not mixed it can separate on freezing and you would find sections that consist mainly of water that have frozen solid and the liquid portions would contain elevated levels of alcohol.  Searching on YouTube for "freeze distillation" should show you some examples.

I suppose this is analogous to normal boiling distillation where the vapor that is generated has a higher proportion of the component with the lower boiling point.   In freezing, the solid that is generated has a higher proportion of the component with the higher freezing point.