How does the next paragraph end?

How to clarify stock
Allow your stock to simmer until the soup's fat floats to the surface.
As you let your stock simmer, the fat will rise to the top creating a foamy buildup.
If there is an excess of foam or fat buildup, it's possible that you have your heat turned too high.
Stock needs to be slowly simmered over a long period of time, not boiled. Typical stocks should be simmered anywhere from 4 to 6 hours long.