Creating an emulsion, which is exactly what homogenization is, does not do anything to the molecules. It reduces the size of the clumps of molecules, which simply allows it to exist in a consistent suspension. It has no effects whatsoever on how those compounds behave in the digestive tract.

Right. Homogenization should not impact fatty acid chain length. Dairy systems are complicated though, and there are protein interactions that help the emulsion by supporting the formation of micelles[1]. It's the same stuff after pasteurization, just distributed differently.

Pasteurization is an entirely different matter though. Heat treatment will convert some fraction of lactose into smaller sugars, including its constituent galactose and glucose[2]. This is why ultra-pasteurized can taste a bit sweeter than untreated milk. Pasteurization also inactivates lipases which would otherwise cleave the fat molecules, reducing the likelihood of rancidity[3].

1. https://books.google.com/books?id=1OhFPZ7tFz8C&pg=PA864&lpg=...

2. https://books.google.com/books?hl=en&lr=&id=6Q8mX8DsDe4C&oi=...

3. https://books.google.com/books?id=gJ6jA7LG-bsC&pg=PA276&lpg=...

How did you learn?

I learned about lipase when I was a kid and followed my dad around at the farm. According to him it was the lipase in the homogenized whole milk that made the difference in taste that I recognized between milk from the storage tank on the farm and bought milk.

Reading up on it now it seems to be a bit more complicated but still.

From a quick reading it looks like homogenization may make fatty acids more accessible to lipase (greater accessible surface area, maybe also charge interactions?). Of course enzyme activity is also a function of pH and temperature. If it was a chilled storage tank, perhaps the taste was different because lipase had not yet had a chance to work--if homogenization happens before pastuerization, it could cause some breakdown after storage but before heat-moderated lipase inactivation.

I have some formal training in biology, but I'm certainly no expert and may be incorrect. What I do know is that dairy systems are complicated.

Maybe that's taking it too far? Clump size may indeed affect absorption, change the time it takes to travel down the intestine, or even change the speed of chemical reaction with increased surface area.

I have examined enough human intestines, macroscopically, microscopically, and biochemically, to feel fairly confident this is not in fact something to worry about.

Not worry about which? Homogenized milk, or shaking it up? Either?

either

It seems a weird sort of naturalism fallacy to assume that mixing milk by hand is optimal. I'd be very skeptical about health benefits, but I'm open to the notion that it tastes different. Have you done a side by side comparison (do some brands offer both?)

this is only anecdotal but in Europe I never had trouble digesting milk. The milk they sell in the US makes me feel bloated. It also tastes differently.

Obviously that's not a scientific study but for me it's good enough to conclude that something is different.

FWIW milk in Germany is also often (most of the time?) homogenized. And it tastes differently depending on the "manufacturer" (the company, not the cows).

*Also PSA: Europe is many different countries, not a single one like the US. So it doesn't make much sense to say "in Europe", because there are huge differences between countries ;-)

To me the main difference is that in Europe it's possible to get unpasteurized milk whereas in the US it's hard to do so.

I am not talking about "H-Milch" in tetra paks :-)

Both Europe and the US are big places with lots of different rules. In the US roughly half the states ban raw milk sales, another 1/4 allow it to be sold on farms, and the final quarter let it be sold either in farmers markets, stores or both. California is on the less restrictive end -- there's a testing requirement and a warning display requirement but it can be sold anywhere.

Not the first time I have heard of differences between US and European milk on HN: https://news.ycombinator.com/item?id=9323380

Sure, but why conclude that the relevant "something" that is different is homogenization?

I didn't conclude that. It seems the major difference is pasteurization and homogenization so I guess it's one of them or both.

I should add that my observations are mainly about fresh milk from a farm. But even the ultrapasteurized milk they sell in tetra paks is better digestible for me.