All recipes call for simmering a dish if you wish to reduce. I know that if for example if I wish to reduce wine, it will take me double the time or even more if I simmer instead of just cranking the heat up to a boil. But there must be a reason for this – what is that? There is only a 6c difference between a simmer and a boil.
I also presume boiling is more permissive in some cases than others, so an ability to distinguish the importance of simmering is necessary to know when you can crank the heat up to save time.
Best Answer
There's another reason for not boiling liquids, besides the possibility of making a mess (boiling over) or ruining it (scorching, etc.).
You actually reduce the amount of flavor by boiling. As Kenji explains on Serious Eats :
So ... if the only goal was to make there be less liquid, boiling's fine. But if you actually want to concentrate the flavors, you want a slow simmer.
The article also goes into more details about reducing alcohol, and some problems with boiling tomato sauce (which I believe applies to most pectin & other hydrocolloid thickened sauces).