Stews/Casseroles etc: Boil before Simmer

[rjchew]

It seems whenever I read a recipe for any kind of stew/casserole/braise, you are instructed to bring the cooking liquid to a boil before reducing to a simmer and cooking at that temperature for a long time.

Does anyone have any idea why you should bring it to the boil first and not just cook it straight from the simmer?

[tedwin]

Boil to kill off any bacteria that might survive a mere simmer.

[technophile50]

To expand on what Tedwin said, the low heat input required to maintain a simmering temperature might raise the temperature so slowly that the food would stay too long in the "danger zone" of temperatures for pathogens. Full heat ramps the temperature quickly through the danger zone, boiling is a convenient indicator of the endpoint(once boiling is reached, changes in power input just change the rate of evaporation, not the temperature) where you can adjust the heat down to match the heat lost, to just maintain the temperature at/near boiling, without excess evaporation. The good thermal coupling, heat capacity of water, and an automatic control mechanism which ramps up the power automatically to compensate for heat load, achieve the same effect for lower endpoints (non-boiling) in sous vide cooking.