Cooking the trinity down is a common cooking practice in the Louisiana
kitchen. You don't do this with every dish, only for the ones you want
to have a special vegetable consistency and color. Examples are gumbo,
stew, jambalaya, roasts, etc. Sometimes you'll want to cook the trinity
down until the vegetables are just wilted.
What I've done here is put together some pictures of the process along
with explanations of each step. I did this batch for a pot roast. I
seared the pot roast, removed it from the pot and continued to cook it
in another pot.
The typical trinity for example would be 4 cups of onions, 2 cups of
bell pepper and 2 cups of celery all chopped. Or 2-1-1
2 onions chopped
On a medium fire with a little oil in the pot I added the onions stir
every few minutes.
I let them slightly wilt and turned the fire up just a little so most of
the onions would turn brown.
One the onions got to the browned stage I wanted I added the bell pepper
and celery. I also added about 1/8 of a cup of water; just enough to
almost cover the bottom of the pot, and, turned the fire down to just
below medium. Stir often.
Here's where you have to watch things a little more closely. You should
keep a little water in the pot at all times stirring every five minutes
or so. Notice below the brown liquid. That is the result of both
browning the onions and searing the roast.
Below, the trinity has cooked a little more. This is probably 45 minutes
into the process.
And finally here is the result 90 minutes later. Notice that it's about
1/2 the original size.
From here on you would throw in the roast, or add browned chicken or
whatever and continue to cook as you normally would.