Gonneke writes:
< Fat is lighter than water and some of the dry components of milk be
heavier than water. So the exact composition of any given sample of milk may
have a slightly other weight per volume (don't know the English scientific
word for the phenomenom that each material has it's own weight per volume
compared to water as 1:1 = gram:mililiter),>
I think the term you are referring to Gonneke, is "specific "gravity".which
also seems to be expressed in the term "density". Some googling brought up
some interesting factoids-one of which is that the temperature at which the
measurement of specific gravity is made, makes a difference.
<Density of Milk
The Physics Factbook <http://hypertextbook.com/facts/>™
Edited by Glenn Elert -- Written by his students
Since fat has a lower specific gravity and therefore is "lighter" than the
milk serum, fat globules rise to the milk surface. . . . . . . Cream or milk
fat is lighter in density than water and floats on the surface of
un-homogenized milk. When you skim off the surface, some of the fat, the
denser portions remains and the milk is denser. This explains why skim milk
is denser. . . . Density = Mass/Volume.. ..>
Google agriculture source (cow milk):
Specific Gravity (Density) (12)
The specific gravity of milk measured at 15o C or 20oC is normally 1.028 -
1,033 kg/litre. The specific gravity depends on the protein and fat
content. The specific gravity of fat is 0.93, solids-non-fat, 1.6 and water
1.0 kg/litre.
(I can't resist quoting some other interesting factoids that bear upon some
other recent posts:
<AUTH HARDING, H. A.; PRUCHA, M. J.
TITL IS ROPY MILK BECOMING A MORE SERIOUS DAIRY TROUBLE
YEAR 1920
JOUR JOURNAL OF DAIRY SCIENCE 3:502
KEY ROPY MILK
< Freezing Point (11)
The freezing point of milk is not dependent on fat and protein content.
Salt is the decisive factor together with lactose. These substances are
completely dissolved. As the quantity of salt and lactose in the milk is
almost constant, the freezing point will be constant too (between - 0.53 and
-0.55 C). Deviations from this show that the composition of the milk is
abnormal and that it has probably been adulterated. >
And an example to remind us that nature is the original "lactoengineer":
<Composition of Camel milk
The most important factor in camel milk is water content. Young camels, and
especially the humans living in drought areas, are in need of fluid to
maintain homeostasis and thermoneutrality. . . . . .With water freely
acessible the water content of the milk was 86 percent, but when water was
restricted the water content of milk rose to 91 percent. . . . . . Thus, it
would appear that the lactating camel loses water to the milk in times of
drought. This could be a natural adaptation in order to provide not only
nutrients, but necessary fluid to the dehydrated calf. Another explanation
can be found when examining the mechanism of sweating in man when exposed to
heat (Ingram and Mount, 1975). Adaptation to heat causes secretation of a
profuse watery sweat. This is caused by secretation of endogenous ADH
(anti-diuretic hormone, secreted from the neurohypophysis) because man
produces the same water sweat when injected with ADH. Thus man loses water
from his sweat glands, allowing him to maintain thermoneutrality. As the
mammary glands have the same embryonic origin as the sweat glands (Strauss,
1974), and as ADH secretation is elevated in the dehydrated camel (Yagil and
Etzion, 1979), it could happen that the loss of water into the milk is due
to the action of this hormone. Injections of ADH into lactating laboratory
rats exposed to heat for 8 hours a day also caused increased water content
in milk (Etzion and Yagil, 1981). . . . . . It is also of importance to note
that the other hormone of the neurohypophysis is oxytocin, the hormone that
is essential for the letdown of milk. Stimulation of suckling and milking
could possibly influence the neurohypophysis and induce secretion of both
hormones and so lead to a dilution of the milk. Whatever the explanation,
the diluted milk at times of water deprivation makes an excellent food for
man. It also explains the Bedouin tales of taking a lactating camel along on
long trips through the desert >
Jan writes+
<For example, if 1 ml of foremilk actually weighed 2 grams, and a ml of
hind milk weighed 1 gram that would be certainly different than if 1 ml of
foremilk actually weighed 1.002 grams vs 1 ml of hind milk weighing
0.997grams.>
Not to worry. The actual weight difference between cream and skim is
apparently not huge enough to make weighing total futile. Besides even if it
weighs less, cream has more calories per volume, so we end up chasing our
tail obsessing about the density inside our baby on the scale, it appears. I
do agree with
Jennifer writes:
<Only water weighs 1 ounce per 1 ounce volume, b/c its density is 1.>
Well, I was ready to pounce on that, of course, because I think this is only
strictly true of the metric system. But to be "fair", since I was thirsty, I
weighed exactly one cup of water (8 fluid oz. ) on my postal scale, and sure
enough, it weighed 8 (averdupois) ounces (close enough for government work,
as we say here in the U.S.;-) I also remember that both a gallon of water
and a gallon of milk each weighs approximately (notice that word
"approximately") 8 lbs. (16 oz. per lb. x 8 = 128 oz per averdupois weight,
while 32 fluid oz per quart x 4 = 128 fluid oz. Well, I'll be durned!!)
Next, I weighed 8 oz. of skim milk, and was going to report, but I remember
drinking it, but not the weight, because that was over an hour ago. (Did I
mention that I must soon force myself to go "no mail" to transfer my
addiction from Lactnet in order to study?)
<We cannot assume that a baby who gains one ounce in weight has consumed one
ounce of milk,>
I don't follow that reasoning, (after my "experiment") but we don't know
what % of fats/ water/protein, etc. that ounce consists
of, so extrapolation to nutrient value becomes questionable and naive, as
she makes in some of her next points:
<nor can you know the composition of that milk, . . . . and of what
composition at the last feeding, nor what the next feeding will look
like. >
Susan writes
<I'd have to look it up, but there was a fairly recent and fairly convincing
study done in Ghana or some country nearby that showed that it was really
the volume of milk consumed from the breast that had far more to do with
weight gain than the fat concentration.>
Over one or more 24 hour days, at least. On the one extreme, rapid weight
gain is one common hallmark of babies when mom has an oversupply and
possible relative lactose overload, because babies can use excess
carbohydrates to create body fat for themselves storing calories they don't
need right away for metabolism. However, on the other end of the spectrum
e.g. premies, when the tummies are small, using extra hindmilk as Paula
Meier has shown, seems to make very good sense.
And then, as Lynnette observes:
<Without "proof" that the baby is getting a certain number
of ounces of milk, pediatricians are going to be pushing more
supplementation than necessary. And it can also happen that
pediatricians are not worried about clearly inadequate intake, and the scale
provides the proof they need that the baby is not getting
enough and does need temporary supplementation, not rectal stimulation.>
Ah, well, where has the morning gone??? I must discipline my ADD tendencies
and get down to other work! LOL. And most of you have many other things to
do besides reading my musings, I'm sure.
Farewell, good friends. I must tear myself away from the keyboard for today!
Jean
******
K. Jean Cotterman RNC, IBCLC
Dayton, OH USA
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