Re: Why milk doesn't freeze?

Milk does freeze! The freezing point of milk is usually in the range of    
-0.512 to -0.550° C with an average of about -0.522° C.  The freezing 
point of water is 0° C.  The freezing points of foods drop with the 
addition of salts, sugars, and other things that dissolve.  The freezing 
points of beer, carrots, etc. are also below 0° C.  I would suspect that 
the freezing points of most products are even lower than milk (for 
example, ice cream is frozen at least several degrees below zero), so it's 
a small mystery that milk was the last thing to freeze in your freezer.  I 
can see how this would happen in a few situations:  
	1.  Your freezer (even though a 1960 model) is extremely good at 
maintaining a temperature just at 0° C slightly below, but greater than 
0.5° C.  This would freeze the water in your products, but not completely 
freeze the milk.  If you can turn down the temperature of the freezer, I 
highly recommend it - for food safety and food quality reasons.  
	2.  Your milk is in the middle of the freezer, closely surrounded 
by other products.  When the air flow inside the freezer is not able to 
reach a product, such as in a very crowded freezer, things will not freeze 
as well.  This is probably the case - I can't imagine a 1960 freezer being 
that efficient.  This happens in my freezer at home when my roommates and 
I cram it full and there is little airspace left.  
	3.  Your milk is not typical.  Is it possible the milk was not 
from a large commercial dairy?  If the milk has a higher solids or fat 
content than normal milk, it would freeze at a lower temperature than 
normal.  

If you make sure the temperature of the freezer is less than -1° C, your 
milk will freeze, definitely!  You can check the temperature with a 
thermometer to double check.  If it doesn't freeze at a temperature lower 
than -1° C, your milk is an enigma to me - send me a sample and I'll test 
its freezing point!  

I hope that answers your question.  

Laura Lebak
Graduate Research Assistant
University of Wisconsin Food Science
1605 Linden Dr. 
Madison, WI 53706
email: lllebak@students.wisc.edu 
Laura's Page