Sheldon wrote:
> hob wrote:
>
>> "Bob Simon" > wrote in message
>> ...
>>
>>> I buy the gallon size of milk, split it into two plastic
>>> half-gallon containers when I get home, and freeze one. After
>>> thawing for a couple of hours, there is still a block of frozen
>>> milk in the center. If I use the liquid milk at this time, will
>>> it be the same concentration as after the whole carton thaws and
>>> is shaken?
>>>
>>
>> I can't speak from direct experience of personally freezing milk
>> However, from chemistry, theory says there should be a slight , but
>> not significant, difference in fat-containing milk, which depends
>> on the rate of freezing-

No. The explanation here for what milk is has important missing components.

>> 1) There are two immisicible liquids in all but skim milks:
>> fat-based and water-based solutions. The water has dissolved
>> sugars, etc. The fat has dissolved vitamins, etc.
>>
>> 2) Homogenized milk is a suspension of fat solids in water
>> solution; the fat is not dissolved in the milk. Homogenizing
>> "breaks" the cold fat into small enough particles that they don't
>> float in the water solution Think cold butter blasted into such
>> tiny particles that they remain as solids suspended in the water.

But that's not what milk is. Cold butter blasted into a water-based
liquid would eventually come out of suspension unless something
prevented the butter particles from touching and rejoining. That's why
milk stays homogenized and a vinaigrette doesn't.

>> (since there is no apparent need to homogenize skim milk, is skim
>> milk homogenized?)
>
> Yes, skim milk is homogenized... skim milk is not fat free, it
> contains about 1% fat.

No. It doesn't. 1% milk has 1% fat. Skim has between 0.1% and a maximum
of 0.5% fat. And it is homogenized to keep that fat in suspension.

> All that you contributed is correct. Modern
> homogenizing methods are very through so milk does not readily
> separate when freezing or thawing, certainly not when using modern
> frost free freezers and thawing, at least partially, while under
> refrigeration... anyone still using old fashioned refrigerators
> should divide milk into smaller containers before freezing, but
> should do the same with all foods.

This is utter nonsense. Homogenization of milk is not simply a matter of
making the milk fat particles small. Homogenization is done by forcing
hot milk through tiny nozzles at high pressure. The fat globules are
reduced from about 4 micrometers down to about 1 micrometer (millionths
of a meter). The fat attracts casein protein particles which adhere to
the fat and create a membrane around each globule which interferes with
the normal fat clumping. That's why the fat stays dispersed. Each tiny
fat globule is surrounded by a membrane that keeps it separated from
every other one and prevents them from rejoining.

Freezers come in two varieties; conventional and frost-free.
Conventional freezers stay to a very narrow range of temperatures by
cycling on when the temperature in it drops below the thermostat setting
by a fixed amount. It turns on the compressor, sucks some heat out of
the freezer compartment and gets back down below that trigger temperature.

Frost-free freezers have much wider variability for temperatures. The
reason that there's no frost in them is because they are designed to
warm the interior of the freezer compartment to evaporate frost. The
evaporated water is condensed onto a coil that gets heated to make it
become water which is channeled out of the freezer compartment to an
evaporator pan where it's heated to evaporate into the room.

Neither kind makes any difference in short-term freezing of anything.
Over longer periods, the frost-free will cause a great deal more freezer
burn because of the temperature variations and subsequent moisture
migration. This is an absolute irrelevancy in the matter of what happens
to milk when frozen. And Sheldon's prattle is, from the viewpoint of
physics, absolutely backwards.

> If homogenized milk were prone to
> separation it would certainly do so while under refrigeration and
> certainly when left at room temperature, it does not, not to any
> meaningful degree.

Given that the fat globules are held separate by proteins that aren't
themselves subject to variations at above-freezing temperatures, this is
just more Sheldon nonsense. He simply doesn't understand what milk is.
And is not.

> Those who claim their frozen milk separates are
> doing something incorrectly, or simply lying... old milk that is just
> beginning to sour will separate much more readily... did I mention
> LYING.

More Sheldon nasty bullshit from the normal complement of Sheldon ignorance.

> Btw, human breast milk is frozen all the time (a very common
> practice), and is not homogenized, leastways not after leaving the
> breast. hehe

Hehe. He said "breast." hehe... Idiot.

The milk will separate into its fat and cream components. The protein
matrix has never formed, so can't be broken by freezing.

>> 3) Dissolving compounds in a liquid lowers its freezing point, but
>> as I remember, adding non-dissolved solids in suspension does not.
>> The dissolved compounds in the solution do not separate out. They
>> freeze evenly. (Think salt added to ice-water to make ice cream to
>> lower the freezing point, and think frozen confections which
>> freeze with the dissolved sugars evenly distributed.)

Not completely accurate. Look at large blocks of ice made from water
than hasn't been de-ionized and boiled to remove dissolved gases.
There's always a cloudy center. Commercial ice makers make clear ice
from moving water for that reason. Home-made ice cubes will all have a
cloudy center. It's dissolved minerals and gases, and they've migrated
to the center.

>> I believe
>> suspended solid particles can be separated out only if the freezing
>> is done slow enough. Think ore refining to remove impurities, and
>> slow freezing with ice extraction used to concentrate solids in
>> suspension.

And think of freeze-distillation of fermented alcohols. The water
freezes out leaving a more concentrated alcohol behind. It can be done
several times, each time concentrating the alcohol further until it
reaches a point where the concentration is so high that it would require
extraordinary temperatures to do it again.

>> 4) Liquids frozen in a container do not freeze all at once
>> (supernatant excluded). There are two conditions of freezing: rapid
>> freezing, where the water crystals in contact with the much-colder
>> sides form first and cool so rapidly they cannot migrate to the top
>> of the solution, and they grow small crystals from the sides,
>> expanding into the rest of the solution, trapping most of the
>> suspended particles in the crystal matrix; and slow freezing, where
>> the water cools and expands and floats to form large-ice-crystal
>> ice on top, ice unable to trap the suspended solids until the
>> convection slows.

This doesn't take into account the nature of milk as described above.
Freezing will disrupt the protein matrix surrounding each fat globule so
that upon thawing, the fat will clump. The protein will, as well, and
change the mouthfeel. Agitation can help to redistribute the fat, but
not to the condition before freezing.

>> Theoretically - The water and water-soluble solids should freeze at
>> one temp, lower than that of water.
>>
>> If you freeze the milk and suspended fats fast enough, it shouldn't
>> separate.
>>
>> If you freeze it slow enough , the concentration of suspended
>> particles will vary, by location, in the container.
>>
>> theoretically.....

And a very nice theory it is. Except for the chemistry and physics of
milk, it's lovely. The complexity of milk, however, removes it from this
view.

I suggest reading "On Food and Cooking" revised 2004 for a much longer
and scientifically clear discussion of milk and everything about it.
Harold McGee is one of my heroes. Good science and good writing.

Pastorio

> ---------
>>
>> Note - due to the expansion of water as it becomes a solid, and
>> that it takes time-in-liquid to create large ice crystals, cells
>> containing water and molecules which attach to the ice crytal
>> lattice are not damaged by very rapid freezing, but they will be
>> damaged by slow freezing due to the large crystal formation. That
>> suggests that taste may be affected by slow freezing.
>>
>>> -- Bob Simon remove both "x"s from domain for private replies
>
>