How does fat affect the precipitation of proteins? I am doing an experiment using milk, heavy cream, and vinegar. We are trying to precipitate proteins from milk and heavy cream.

When I did the experiment with milk, it was very quick reaction and easily to isolate the casein polymers with vinegar added to the heated milk. This does not occur when the same process is used with heavy cream. I have tried to find out how this process fails with the heavy cream online and in my book there is a decent portion of the chapter dedicated to fats, but it doesn't mention why polymer creation can not occur in this experiment.

Can some one please help me with the reason the heavy cream doesn't curdle?
Casein is the main protein in milk. When you perform the polymerization experiment, the result is an "aggregation" of said protein, which gives the product a solid consistence.

Products such as butter and cream are made with the fats from milk (not the proteins!), hence they are almost casein-free. Of course, being them almost without proteins, the polymerization doesn't occurr.

If you look up the nutrition facts of milk and heavy cream, you see that proteins constitute the 20% of calories of milk, and only the 2% of heavy cream.