Making stock from scratch can take a long time so when you do make it, be sure to make a lot. Whether it is a seafood, chicken, beef or vegetable stock they all freeze well. The nice thing is you don't have large containers, but neat little discs stacked in freezer bags which takes up less room in the freezer. Pop out as many frozen discs as you think you will need for the dish you are making. They last in the freezer for up to 6 months or longer if you get the air out of the bags before sealing.
Ladle the demi glace in muffin tins (I also use this method when I make shrimp stock. See a photo of the discs and the recipe for making shrimp stock in my recipe, Garlic Shrimp with Fettuccine.)
I already dipped into my stack as I was having beef for a dinner and wanted to make a sauce to go along with it. Love the convenience of having discs of stock at the ready to spruce up any of my meals.