Final answer:
The mass that forms and rises to the surface when making a consommé, which should not be stirred once formed, is called a raft. This raft is essential in the process of clarifying the broth and trapping impurities.
Step-by-step explanation:
The mass that forms when making a consommé, and which one should not stir after it has formed, is referred to as B) A raft. This raft is important in the process of clarifying the consommé as it helps to trap impurities. When you are making a consommé, you effectively create a filter out of solid ingredients like ground meat, mirepoix, and egg whites. As the broth simmers, the raft rises to the surface, bringing along with it the fine particles and proteins that can cloud the broth. It's crucial to avoid stirring the consommé after the raft has formed to ensure that the clarification process is not disturbed and the broth remains clear.