Can cornstarch get too old?
Thickening with cornstarch has always been hit or miss for me - today I thickened some fabulous (IMHO) lamb jus (about 1.25 cups) with the properly done slurry of cornstarch (1 tbsp CS/1 tbsp cold water) ...... and nothing material happened.
I served it anyway - it was delicious but I would have liked it to be thicker. Reducing it further wasn't an option because the flavour was perfect.....reducing it would have made it too salty/too acidic.
I make a great roux for gravy but didn't want that effect for the lamb jus.....maybe try arrowroot?
My favorite for thickening is a buerre manie.. A mixture of flour and softened butter. You just keep adding at the end until you have the desired consistency. You do get a nice butter flavor.... Not sure if that's what you want.
MIL used arrowroot never corn starch. I've never used arrowroot rely on corn starch.
can it lose its' umph, prob. it's only about a buck-I'd toss yours & get a new Argo.