For a Clearer Stock, Simmer; Don't Boil
Yes, it takes longer, but sometimes there's a good reason for cooking low and slow when making stock.
Nearly every recipe for the classic French dish pot-au-feu (see related content) calls for simmering rather than boiling once the meat has been added to the pot. Yes, this means you’ll be cooking the meat for upwards of 3 hours, but there’s a good reason for cooking low and slow here. Just as when you’re making stock for soups or stews, boiling will cause soluble proteins and rendered fat to emulsify into the cooking liquid. By simmering, you avoid emulsifying the fat and thus keep the stock clearer, and we found that the scum created simply settled to the bottom of the pot.