[paul.fr]

I got some new milk today and noticed that it was "homogenised"! What have they done to my milk and why did they do it?

[daveshorts]

Milk is made up of lots of globules of fat suspended in water. They are big enough that over several days they will float up to the top of the milk and separate from most of the liquid.

Homogenisation involves squirting the milk through very small holes; this breaks up the fat globules so that they become so small that thermal vibrations and currents in the milk are large enough to keep the fat mixed; this means that in future it won't re-separate.

[another_someone]

Milk is made up of lots of globules of fat suspended in water. They are big enough that over several days they will float up to the top of the milk and seperate from most of the liquid. Homogenisation involves squirting the milk through very small holes, this breaks up the fat globules so small that thermal vibrations and small currents in the milk are large enough to keep the fat mixed into the milk, so it doesn't seperate out.

Yes, I remember in my childhood, when real milk (OK, not that real - I have never tried green top milk - that is I believe illegal to sell) when the cream was always at the top of the milk.

[eric l]

For what it's worth :  I've been told than an other advantage of this homogenization is that the milk becomes more suiteable for spray drying (= making milk powder).  For what that is worth, because most milk powder nowadays is "non fat" or "low fat", meaning that the spray drying is done on skimmed milk.

[JimBob]

In the evolution of milk processing, I too remember when the cream was floating at the top of the rest of the milk. I still buy homogenized whole milk. Yet it isn't whole. In this country, milk always had less cream content that the cow put there. This was to allow the dairy to put cream into little bottles for coffee at restaurants, make ice cream, etc.

All of the processing for skim milk was, and I  remember the controversy around it, actually a plan by the dairies to allow them to make more profit. People were actually VERY riled up about loosing the taste. It was not until AFTER the diaries started doing this that they came out with the idea that it was a diet drink and still later that it was better for you.

If human mothers produced skim milk there wouldn't be many children surviving to 1 year old.

[another_someone]

It is rather dubious that skimmed milk is actually better for you.

Skimmed milk does have less fat, but as we have discussed elsewhere, if you have less of one thing (as a percentage of the whole) it means you have more of something else, and if milk has less fat, it typically means it has more sugar (lactose) - that is unless all they do is water it down, so you get more water.

[DoctorBeaver]

I've noticed that since homogenisation, blue tits don't attack bottles of milk on the doorstep.

[Bored chemist]

For a given volume, skimmed milk has fewer calories. For a lot of people that's a health benefit.
On the other hand, removing the fat also removes the fat soluble vitamins. These might get added back later (the law in the UK requires that margarine is fortified with vitamins; the same might be true with skimmed mmilk).
Personally I don't like the skimmed product; it tastes "watery" (Yes I know that doesn't make sense, but it still tastes watery to me).

[paul.fr]

For a given volume, skimmed milk has fewer calories. For a lot of people that's a health benefit.
On the other hand, removing the fat also removes the fat soluble vitamins. These might get added back later (the law in the UK requires that margarine is fortified with vitamins; the same might be true with skimmed mmilk).
Personally I don't like the skimmed product; it tastes "watery" (Yes I know that doesn't make sense, but it still tastes watery to me).

I thought i was the only one that thought, skimmed milk tastes watery!

[another_someone]

For a given volume, skimmed milk has fewer calories.

Does it?

It has lower fat, but higher lactose - that is a trade (after all, it must contain something), but does that make for lower calories overall?

[chris]

I think the blue-tit milk-attacking phenomenon may be due to a reduction in the number of milk bottles with foil lids delivered by milk men. The majority of milk purchased in the UK now comes from supermarkets in plastic 4 pint bottles.

There's also been a big drop in the small bird population, which is probably part of the story.

And to address the health benefit / dysbenefit of skimmed milk, fat has a very high energy density - in fact about 8 times greater than carbohydrate (sugar). So you'd have to put in a huge amount of supplementary sugar to come close to the number of calories removed by skimming off the fat.

Also, cow's milk is high in saturated fat. This elevates cholesterol and increases the risk of heart disease, so heavy milk consumers would be doing themselves a metabolic favour by switching to semi or skimmed varieties.

Chris

[another_someone]

But does not whole milk have a lower GI, and so a slower release of calories (hence why high sugar foods/drinks are used as sports/energy foods/drinks, but high fat foods never are - no point in getting all of your energy only after the race is over).

Again, another diet, which I grant is not without its controversy, is the Atkins diet, and this actually suggests that saturated fat is not the primary risk as far as calorie intake is concerned (it does not address the wider issues arterial health, or other health risks, only the issue of weight loss, against which it has demonstrably worked).

[chris]

Sorry, I only just saw this, hence the tardy reply.

Milk may well have a lower glycaemic index, but the fat it contains will be efficiently absorbed and stored within the body. Fat is usually what makes people fat, not carbohydrates. Fat burns in the metabolic fire created by carbohydrates, but only if fat needs to be burned. If there is ample energy available already then fat is simply stored.

Chris