When you separate cream from whole milk, what is left over?

In modern dairy processing ALL the cream is extracted from the milk, so what's left behind is skim(med) milk.  Then cream is added back in a controlled process so that you get whatever percentage of fat the milk is labelled as.  It's also homogenised (the fat particles are ripped apart) so that the cream doesn't float to the top of your 2% milk.  If you are old enough you might remember how before homogenisation the cream used to rise up in the milk bottles and also how the cream in the milk would cling to the sides of the glass when you drank it.  

In the old days skimming the cream off was an inexact science because it was done by hand.  If you wanted richer milk left over, say for cheese-making, you had to use your own judgement.  Also, the natural amount of fat in milk varies throughout the year.  In high summer whole milk straight from the cow is very rich and has a different nutritional profile to natural grazing autumn or winter milk.  Supermarkets and big dairies have trained their customers to want the same product all year round, so it has to be artificially created.

Unless you get it from a dairy, all milk is homogenized and you cannot separate it. 

Skim milk is left over.

2% milk has 2% of its total weight being fat (cream).  Skim milk is 0% fat in the milk.

Whole milk has the cream homogenized into the milk.  

Raw milk is like skim milk with the fat/cream rising to the top in a layer if you let it sit in the fridge.  Skim it off and make butter from it.  If you shake up raw milk the fat/cream is in streaky strands through the liquid part of the milk.

HOW much cream is contained IN the raw milk, as it comes out of the cow, depends on the BREED of the cow.  For instance, both Jersey and Guernsey breeds have the highest fat/cream content in their milk, but they don't give as MUCH milk per day as the Holsteins (the black-and-white cows), so most dairy farmers keep Holsteins.

And that's all I have to say about that!

If you separate all the cream from the milk, you then have skim milk left over