ELI5/How does beef stock become thick of fat and water don’t, usually, mix?


Like how does cooking it down make a thick Demi glacé or how does one get a gelatinous broth/stock?

In: 0

It’s not fat that is making the stock thick. There is lots of collagen and minerals that come from the bones and joints as you cook them down. That’s how it becomes gelatinous; when it cools it’s just like jello.

The fat doesn’t mix with the stock. When you make stock, fats float to the top and you either skim it off or put it in the fridge and remove the solidified fat. Stock gets thick because you convert the collagen in the connective tissue into gelatin. That’s why when you make stock you generally make it from joints

The word you’re looking for is ’emulsion’, (technically a *colloid*), which means an extremely consistent mix of a liquid, and very small, well-dispersed bubbles of other liquids or other states of matter.

An emulsion will be chemically and physically stable enough to hold those little bubbles in suspension, at least at a certain temperature, for a while. This can range from a vinaigrette dressing to Hollandaise to stock.

Gelatin and other protein lattices go a step further, by linking up once they’re dispersed in a mixture and trapping a lot of those other bubbles in a ‘net’. That’s what keeps a lot of thick mixtures, well, *thick.*