Simmer over medium heat until reduced to 1/4 cup, about 30 minutes.

Simmer over medium heat until soft, about 30 to 40 minutes.

Simmer over medium-high heat until reduced by half, about 10 minutes.

Simmer over very low heat for two hours, skimming often.

It is then covered and left to simmer over very low heat for at least 1/2 hour without stirring.

Simmer over medium heat until tender, about 10 to 12 minutes.

Simmer over medium heat until reduced to 2 cups, about 30 minutes.

Simmer the mixture for an additional 10 minutes over very low heat.

Simmer over medium heat until the water is reduced to 1/4 cup, about 10 minutes.

Simmer over medium heat until tender, but not soft, about 20 minutes.