boil off

1. To remove a liquid through evaporation as a result of boiling. A noun or pronoun can be used between "boil" and off." You'll need to boil the excess water off before the solution can be used. Don't worry, you'll boil off the wine in the process of cooking the sauce. If you don't put the pasta in the pot soon, you'll end up boiling all of the water off.

2. To be removed (from something) through evaporation as a result of boiling. Even though there is cognac in it, the alcohol boils off when the dish is being cooked. As the water boils off, the sauce will thicken. It'll have a better, more condensed flavor once the stock boils off.