Demi glace is the base to many of the most classic sauces in french cooking. Demi on its own is a terrific sauce as well. This is the base we use for our braised beef dish at Cacio Pepe. I recommend you read the article on beef stock before reading this, as this sauce is based off a beef brown stock that is made correctly. Anyone that has talked to me about cooking for more than a minute, knows that I throw around the word "classic" all the time. I am all about the classics, and everything should be made a certain way, the original way. This is about one of the only times I would disagree is with this classic sauce. A classic demi glace sauce is made by mixing equal parts brown stock, and espagnole sauce. An espagnole sauce is essentially a brown stock (minus the beef bones) that has been made with beef stock instead of water, and there is an addition of flour as a roux, to thicken the mixture. The beauty of this is it costs about half as much in food cost as the way I am going to show you, the disadvantage of this is the colour, and flavour are not particularly close. Demi glace sauces are usually the most expensive in the kitchen, and for this reason they are usually reserved for fine dining restaurants, that can eat the food cost in the price of the meal a little better than your average mom and pop.
The method in which we are going to use for this demi glace is straight reduction. There are only two ingredients; beef stock, and red wine.
Step 1 - Cook down your red wine
You are going to start by cooking down your red wine in a heavy bottom pot, till it is almost syrupy in consistency.
Step 2 - Add your beef stock
Step 3 - Simmer the mixture, and cook down
You are going to cook down the beef stock mixture by around 1/6 to 1/8 in volume. It will become thicker, and syrupy.
You should be able to coat the back of spoon, and when you run your finger across the spoon, the liquid does not run down the cleaned portion of spoon.
Step 4 - Strain the Demi Glace
First strain your demi through a fine sieve, and then strain that mixture through a coffee filter.
For over 2 litres of beef stock, you don't end up with more than a couple of ounces.
Finished demi glace
You may not end up with a lot of sauce at the end, but what you do end up with is one of the most flavourful sauces, and most common french sauce base’s there is.