Why does speed of boiling effect fat rentention in soup?

The amount of fat, saturated as you put it has very little to do with the solidifying of gel in the soup. This is based on the amount of bones used and the time cooked..

Fat left in a soup to me does two things, It keeps the soup hotter and makes it greasy.

     I dont believe when correctly executed a soup is enhanced by leaving fat in it. To make a stock most times everything starts from a cold state., To make a consomme everything MUST start from a cold start. To control simmer and boil and  a rolling boil is a matter of controling the heat and its source. Water alone boils at 212. Stock and soups sometime take  higher temps because they are concentrated solids at times and not simply water.

     Similar to if you pour 2 cups of coffee and put sugar in one and drop some from each cup on both legs. The leg with the cup with sugar added will develop a worse burn and if a thermometer is put in, will in fact be hotter. So goes science.

Boiling a soup breaks up the pools of fat. It essentially whisks the fat into the broth creating a cloudy emulsion. And for most people an unpleasant soup, but you've posted before that you like it. The same amount of fat is created by either method essentially, but by not boiling the stock, the fat remains visible and is easy to remove.

As chefed noted, gelatinous quality comes from bone and cartilage normally when you make the stock.

Chinese soups are usually thickened with a cornstarch slurry near the end.

Meat is added later in the making of soup so it doesn't overcook and lose it's texture and taste.

Managing heat to hit a simmer is an art and has a lot of variables. Generally it's easier for a cook to bring to a boil and back off to a simmer than to creep up on the simmer without overshooting. As the soup loses heat and comes down to a simmer, you can sometimes overshoot the other way too.  Induction, you can set a temp and hit it. I can set my induction burner to 180 for making a stock and it does a very good job.

Fat can contribute to flavor, but is not necessarily flavorful itself nor pleasant to eat. In a situation such as soup where the fat doesn't mix with the water well, it's generally percieved as unpleasant. If you were to boil the stock and fat to emulsify it, the flavors are often murky and not clean, crisp and pleasant. Mouthfeel also suffers with the fat in the soup.

Sometimes, fat may be added to a soup as a garnish such as using an extra virgin olive oil on a bowl  of minestrone.  This is a case where the fat is particularly flavorful and accents the soup, as well as being a healthy, beneficial fat.

When boiling the fat gets mixed up directly into the broth.  It's not going away at all or being removed. Boiling makes it impossible to remove.

Simmering makes a clearer stock than boiling. Scum/froth will still rise to the surface if you're truly at a simmer.

Neither simmering nor boiling makes the soup high fat. Simmering just leaves the fat visible. When boiled, the fat is still there, just not easily visible to the naked eye.

Simmering is high enough temp for food safety, 180-190 with some variation by your elevation.

The general principles of cooking are to not make a high fat soup which is why simmering is considered the better technique as it leaves the fat on top for easy removal.

Phatch I notice you said you have an induction burner. I was thinking of getting one for the house. What brand is it. How long have you had it, and what do you think of it. Thanx EDB

I reviewed my unit here:

http://www.cheftalk.com/t/63404/max-burton-6500-induction-burner

I've not checked to see if models have changed since then.

I think you want something like tonkotsu broth.

Yes, some fat is carried up in steam. Not lots.

You can taste it. It's why it tastes disgusting. Animal fat generally doesn't taste that good.

It's been broken up small enough that there is insufficient surface tension for the pools of fat to reform, i.e. has formed an emulsion.

Too many variables to give you a for sure answer. Fat contributes to satiety, but it takes very little for this effect to register on the body. I suspect it's more likely that the visual appeal and flavor of a simmered soup contributes to your perception of satiation. And you probably eat more of the soup you like compared to the soup you don't. You seem to be attributing effects to visible fat that aren't supported in the science.

No. You've taken certain aphorisms and perceptions as fact that aren't the truth you think they are.  You should read Harold McGee's On Food and Cooking for a better understanding of the issues I think.

Sounds like fat. If you like it, eat it. 

Perhaps Eating Christmas in the Kalahari will show how this is a cultural divide.  They delight in fat the way you do and others here do not.

http://windward.hawaii.edu/facstaff/dagrossa-p/articles/EatingChristmas.pdf

Chlorinated,

Your questions appear peculiar for a "recent culinary school graduate". Perhaps you should consider asking for a refund of your tuition.

What culinary institution did you attend or graduate from???

I think it can be tasted, but different people have different capacity to taste.

Chlorinated. 

Again what school are you in or did you graduate from???

Hey Chlorinated are you trying to make a broth based high fat soup? If I were going to try and make a high fat soup I would not do a broth based version I would do a cream based. Cream is fat and so you would achieve what your a looking for. Another option for what you (I think) are trying to accomplish is to try and introduce the fat to the broth based version in different ways. For example introduce fat by adding dumplings or quenelles.

I am pretty much in agreement with what everyone said previously. To get the nice think gelatinous soup you start with lots of bones. You can add meat but it has to be well marbled and this is quite expensive. In fact it was actually what Escoffier did in his days which is amazing but of course back then they were also tourneing black truffles. Unless you have a big budget I would not add meat just for the sake of fat I would add more bones.

In regards to what Phatch said about more animal fats are undesirable I find I am very fond of duck fat (great for sauteing vegetables in instead of butter) and of course our beloved pork fat.