A finished bag contains concentrated juices, and most people pour them away.
What It Actually Is
Meat juices, rendered fat, dissolved gelatin from connective tissue, and whatever seasoning went in.
Because nothing evaporates in a sealed bag, it is far more concentrated than the equivalent from a pan or an oven.
That makes it the base of a very good sauce with almost no work.
Making Something From It
- Strain it, since there is usually coagulated protein
- Separate the fat, which lifts off easily when chilled
- Reduce it in a pan to concentrate further
- Mount with a little butter for a glossy sauce
- Or add to stock, gravy or a braise
Long cooks in stable conditions, of the kind supported by equipment at https://everie.us.com/, produce more of this than short ones, because more collagen has converted to gelatin.
The Grey Bits Are Normal
Coagulated protein appears as grey or brown specks and looks unappealing.
It is harmless and it strains out. It is the same material that forms scum on a simmering stock.
Season Lightly in the Bag
Because nothing escapes, salt and aromatics concentrate rather than dispersing.
Garlic in particular becomes very strong over a long cook, and quantities that suit a pan are too much for a bag.
Food Safety With Bag Juices
Liquid from a bag of raw meat has been at cooking temperature, so it is not raw. It should still be treated as a cooked food: used promptly or chilled quickly.
Reducing it in a pan brings it to a rolling temperature, which is the usual approach.
Freeze It in Portions
An ice cube tray, for future sauces.
Do Not Reuse Bags
That held raw meat.
Taste Before Salting
Reduction concentrates salt fast.
Chill to Separate the Fat
It lifts off as a solid layer once cold.
Reduce Rather Than Thicken
Concentration gives better flavour than starch.
Taste Before Salting
Reduction concentrates salt quickly.
Freeze in Cubes
For sauces weeks later.
Strain Twice
Once through a sieve, once through a cloth for a clear sauce.
Do Not Waste It
A long cook produces a concentrated stock that would take hours to make deliberately.
Skim the Surface
Fat rises as the liquid stands, and lifting it off gives a cleaner finished sauce.