Re: Chemistry Question: Thawing Frozen Milk

hob wrote:
"Del Cecchi" <cecchinospam@xxxxxxxxxx> wrote in message news:3m3sb9Fvfr3lU1@xxxxxxxxxxxxxxxxx

hob wrote:

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 depoends on the rate of freezing-

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.

No. Fat in milk isn't a liquid until it gets above about 93°F. Until then, it's a solid.

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.

You can't make a fat stay in suspension unless there are other mechanisms in action to prevent the clumping of fat globules. If they could aggregate, there would quickly come a point in which they would clump and float to the top. Like in unpasteurized milk.

"Initially, the milk fat exists as tiny globules in the milky starting mixture. Milk proteins on the globules' surface work as an emulsifier to keep the fat in solution. To make the ice-cream structure, these fats need to be destabilized so that they coalesce into larger networks."
<http://pubs.acs.org/cen/whatstuff/stuff/8245icecream.html>

(since there is no apparent need to homogenize skim milk, is skim
 milk homogenized?)

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. )

Adding salt to water doesn't lower the temperature of the solution. It lowers the point at which the solution will itself freeze. This is a bizarre misunderstanding of the physics at hand.

Frozen confections will freeze evenly if frozen extremely quickly, as in nitrogen dipping. Make a sorbet in your home freezer without turbulence and see how evenly it freezes. Or a granita which, by every recipe, needs to be stirred so the flavors and sugar are dispersed.

Make your own ice cream and see the physical and chemical process in action...
<http://www.usoe.k12.ut.us/curr/science/sciber00/8th/matter/sciber/phaseact.htm>

This is so incorrect.

Try the basic chemistry class, oh very wrong one.

Try the basic empirical ice cream freezing class oh theoretical blathering one. Just like people have been doing it for a couple centuries. And it's more physics than chemistry.

Here's one with pictures to make it easier for your scant comprehension to envelop and make all yours. <http://houseandhome.msn.com/Food/Old-FashionedIceCream0.aspx>

And here, buzzwit, is what the ACS has to say about ice cream (and the structure of the fat globules in homogenized milk which I put above, since you obviously didn't get it the first time around). Real science guys talking there, Sparky, not theoretician buffoons: <http://pubs.acs.org/cen/whatstuff/stuff/8245icecream.html>

May I refer you to an introductory text on Chemistry from the University of Minnesota, re Zumdahl, Houghton Mifflin, 1997 pp 529-530?

"FREEZING POINT DEPRESSION When a solute is dissolved in a solvent, the freezing point of the solution is lower than that of the pure solvent."

Lovely, but irrelevant. It's ice and salt, not water and salt. And the freezing point of the solution is irrelevant to the discussion. Adding salt to water lowers the point at which that solution will freeze. Nothing to do with making ice cream, only to do with freezing salty water.

think anti-freeze. Perhaps the knocking sound in your universe in winter is the ice chunks formed in your engine rattling around as the
water-ice "freezes out" of the anti-freeze? In mine, the mix
freezes as one. 

Really? Your anti-freeze freezes?

Do not confuse vapor state phase changes with solid state phase changes.

Do not introduce irrelevant prattle. Making ice cream is liquid to solid state change.

note also on page 28 of the text that the methods of separating liquid components are listed as distillation, filtration, and chromatography. Not freezing.

Do lose the theoretical foolishness. Any school kid knows you can concentrate the alcohol in a fermented fruit juice solution. You put the container of low-percentage-alcohol wine into the freezer and leave it there overnight. Tomorrow, you remove the ice and the hygrometer floats a little differently.

Paracelsus commented that if a glass of wine were left out in freezing weather, it will leave some liquor unfrozen *in the center* which he said was better than heat-distilled alcohol. [emphasis added] Asian nomads did the same with their fermented mare's milk - koumiss - and apple brandy - applejack - was made in colonial America the same way.

Freeze-concentration retains sugars and volatile flavors better than heat distillation and, so, leave a fresher taste to the finished product.

Also see Handbook of Chemistry and Physics, p 15-21, tables of Cryosopic constants and the description of temperature lowering by addition of solute and its calculation.

Have you ever frozen anything in your life? Ice cubes with disolved oxygen? Lemonade? Beer? The water or the material with the highest freeze point separates and freezes first. The old trick of partially freezing hard cider to increase the alcohol content is another example.

Ice cubes with dissolved OXYGEN? The highest freeze point separates FIRST?

Ice cubes with dissolved gases, oxygen among them. Absolutely. That's part of the cloudiness in your ice cubes at home. And minerals. Or is there some other theoretical explanation on some other page of that book you so desperately misapply?

The highest freeze point means the highest temperature at which anything in the mix will freeze. Water freezes out of the cider before the alcohol because it has the higher freeze point of the two.

"This freezing-point depression is a colligative property arising from the sugars and salts in the ice-cream solution. As crystals of pure ice form, the solution's sugar and salt concentration increases, depressing the freezing point further."
<http://pubs.acs.org/cen/whatstuff/stuff/8245icecream.html>

You are on the wrong end of state-change energy, my friend. We are not talking distillation due to vapor energy differences, we are talking solid from liquid. 

You are blathering about irrelevancies in the face of practical experience.

As to the old cider "trick", done here a few times in my youth -

Apparently your youth didn't include the low-tech approach. Leave a bucket of fermented cider outside in the winter and pick out the hard stuff (we science types call it "ice") so you don't have to drink as much to get that lovely warm-ear feeling. And if the day is cold enough, you can do it again to make the ears even more appreciative.

works only

IF you a) filter out the ice or b) have it so very damn cold and still outside that ice forms on the margins and top of the tub from stratification of the lighter colder water, and heat loss from evaporation at the surface, and you pull the ice off the edges. See my original post as to how this occurs. 

<LOL> Blah, blah, blah... Theory rampant; no correlation to the real world.

Ice cream freezers put salt on solid ice, not water.

Apparently you didn't read the instructions carefully. "Liquid contact improves conduction of heat out of the mix, and added salt lowers the freezing point of the salt-water mix up to the saturation point."

Apparently you've never made ice cream. Putting ice around the dasher tub and sprinkling salt on it causes some of the ice to melt, so there is liquid contact and, thus, more efficient heat transfer, but there's still plenty of ice at the end of mixing/freezing cycle.

And the dasher has, among others, the job of insuring even dispersion of flavor and texture ingredients. They don't do that by themselves.

Pastorio

You remind me of the guy in the federal express commercials. You don't get french benefits.

snip

-- Del Cecchi "This post is my own and doesn’t necessarily represent IBM’s positions, strategies or opinions.” 
.

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