When I follow a recipe for a sauce it often talks about reducing by half (or whatever) to "thicken". But that *never* happens to me - it simply doesn't change in consistency at all until I have about only a tablespoon left in the pan.
For a while I'd just presumed it was me lazily using supermarket liquid stock (e.g. http://www.waitrose.com/shop/ProductView-10317-10001-13303-Waitrose+Cooks%27+ingredients+chicken+stock)
but I recently made my own chicken stock, and that is pretty much the same (made from a roast chicken carcass).
Is there just a missing assumption here that the stock to use is heavy in gelatin? Or what?
Why don't supermarket stocks like the above thicken? Same goes for their beef.
I can always use a cornstarch slurry, but I'd like to understand why my experience doesn't match up with any of these recipes...