I have pots simmering now. I beg for friends turkey carcasses after thanksgiving, and added to all the chicken scraps I collect over the year, I get about 60 quarts. I have been doing this for about 14 years.
I simmer and strain, simmer and strain until the strained water is cloudy and almost white. I mix it all together and cook it down. I also add veggies - a mire poix with the addition of parsnips (not this year though - more in a minute).
I skim off the fat (I usually get about 2 quarts of schmaltz, and add a bit of that to the cats food during the winter).
In years past, I take the condensed broth and put about 1 cup in a quart jar, then add water to the fill line. It is based on color and flavor, but I have to condense it as I do not have a pot big enough to make sure everything gets mixed up.
This year, I am doing it different. This year I am taking my broth and simmering it down until it starts smelling "done" - like the water is all gone and it is going to burn soon. Then I will mix it with a heap of salt (I do not generally salt my broth) and some finely-ground dehydrated veggies and herbs, and dehydrate the whole mess. And then blend to a fine powder.
I make my own bullion. After I did it last time, we made it up with a cup of water and measured the powder - it turned out that 1.5 teaspoons made 1 cup of flavorful broth. And I could get 32 "quarts" of broth into one quart jar. I do keep it in the fridge, but that is just my paranoia. I am hoping to get 1-2 more quart jars in the fridge by New Years.