The Basics: Demi-Glace
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Sauces are my favorite part of cooking, from ketchup to béarnaise. Since I love (and aspire to) French techniques, a good chunk of the sauces out there are based on some form of stock -- vegetable stock, chicken, fish, beef, veal, lobster, lamb, duck, and so forth.
Making stock is usually a pretty simple thing to do, but there's a technique used to take a certain type of stock to the next level of culinary refinement -- demi glace.
We did a post about chicken stock a few months ago, and if there's only one kind of stock a kitchen is able to keep around, chicken stock is a pretty good stock to have on hand. Chicken stock can make a sauce base for a huge variety of foods, from green beans to lobster.
A more refined stock for sauces is veal stock. Veal stock itself has a somewhat meaty taste, but it's more umami-ish (is that a word?) than beefy. It's neutral, flavorful, and has a lot of "body". Since veal bones have a lot of natural collagen, long simmering releases a lot of gelatin into the stock, which makes it denser than water and tricks the mouth into thinking the sauce is fattier than it is (gelatin is virtually free of calories or nutrition, even though it's a protein).
Dark veal stock used to be the base, with tomatoes, to make a mother sauce called espagnole. Espagnole would then either make other, derivative sauces, or it could be reduced and reduced and reduced until it, as August Escoffier once wrote, "reached the limit of perfection". The demi glace.
Demi glace (half-glaze) is thick and concentrated stuff. Bullion cubes and "beef base" (that sticky stuff in a jar) are forms of imitation of demi glace, and beef base can sometimes used as a substitute if the salt can be controlled. Typically, a tablespoon or two (or five) is put into a sauce for four people, and the umami and body will permeate the sauce, giving it a boost in richness.
For some chefs, like Bourdain, demi glace is kind of a secret weapon, and it is a nice stealthy way to give a refined kick to virtually any food, from an improvised pan sauce to a bloody mary.
Refining really is what's going on here. From eight quarts of veal stock, I ended up with two to three cups of demi glace. The essence of veal stock and tomatoes -- umami, body, color, smoothness -- are concentrated, and the unnecessary bits -- water, coagulated proteins, off flavors -- are evaporated or skimmed out.
Due to its low-water, high gelatin content, demi glace freezes really well and doesn't always have to be defrosted to use it. Pull it out of the freezer, dig a spoon into it, and a couple tablespoons can be extracted like scooping sherbet. Used in this way, two to three cups lasts half a year or more in our house.
It does take two to three days to make, however.
Veal stock must start with, of course, veal bones. Our town in Florida has no supply of veal bones (and I've searched). We could make osso bucco every week and keep the bones, and I've also liberated the occasional scrap bones from the local store, but I haven't found a steady source other than the Internet. However, I was in Atlanta on business last month, and I accidentally found a butcher store that sold them frozen, so I bought ten pounds, stuck them in a cooler, and took them back with me.
I placed my bones in a single layer in two roasting pans, and put them in a 400 degree oven to brown. The browning will provide flavor, but it will also helpfully get rid of some of the junk that would otherwise cloud up the stock.
The bones must be flipped so they don't burn on one side and create really bitter flavors. I flipped mine every 15-20 minutes. After about an hour, the bones are lightly browned.
I made a mirepoix of carrots, onions and leeks and chopped them roughly.
(leeks get gritty, so I cut them in half, rinsed, then chopped)
The vegetables are added to the roasting pan, and the whole thing goes back in the oven for around 45 more minutes, until the vegetables are roasted and the bones are nicely browned.
Peterson uses a 20 quart stockpot, but I only had a 10 quart and an 8 quart, so I split my bones into two batches, adding them to my stockpots, with the vegetables on top.
Water is added to cover the bones by one to two inches, and both stockpots are set to medium low heat to slowly come up to a simmer.
Peterson's technique calls for deglazing the roasting pans and adding that liquid, but unfortunately my veal bones had a lot of fat attached where I couldn't remove easily, and the bottom of my roasting pans was more fat than substance, so I discarded it.
If I were just making veal stock, that would be it for a while, but demi glace is a form of sauce espagnole, which requires tomatoes. So, a single small can of tomato paste is added to both stock pots.
If the stock is boiled, or heated to simmer too quickly, impurities will emulsify into the stock and make a cloudy, off-tasting liquid. So, I set the heat so that it didn't simmer for 30-45 minutes, then lowered the heat so that it stayed at a gentle bubble or two every second.
The impurities that we don't want are kind enough to float to the surface, where they can be skimmed off periodically.
Chicken and fish stock can be made in a couple hours. Vegetable stock can be made in 30 to 40 minutes. Veal bones need a lot more time to extract gelatin from thicker bone tissue, so I simmered this for about 20 hours. When the water level evaporated to reaching the bone, I added more (cold) water until it was a few inches over the bone level again.
After 20 hours, I removed the bones, then strained the stock using a fine-mesh strainer into a big stainless bowl.
I placed the bowl in an ice bath (I use a cheap punch bowl) to rapidly cool down to room temperature. This is a primarily a hygiene thing -- warm beef stock was used for decades as a bacterial culture medium because it's everything a bacterium loves to grow and reproduce. Dropping the temperature quickly doesn't give bacteria enough time to get a footing. Also, putting eight quarts of simmering stock in the fridge would probably warm everything in the fridge up before the fridge could get around to lowering the dense liquid.
As the ice melts, I use a baster to remove water, and I add more ice.
Once cool, I put the stock in the fridge so the fat will rise to the surface and make it easier to remove. All of this, from the ice bath to the fat removal is an optional step -- the stock can be reduced immediately, but I like getting the fat out beforehand so it doesn't potentially emulsify into the demi glace. There's no real labor involved (it just sits in icewater or the fridge until cold), all it takes is time.
After 20 hours of cooking and about 8 hours chilling, the fat is solidified and I scrape it off.
I put the stock back into a stockpot and bring everything up to a stronger simmer (yet still not a rolling boil).
This is the concentration step. In Escoffier's day, a lot of chefs would throw in a ton of roux, cook until the flour taste is skimmed out, then call it demi glace. No chef seems to do that these days. Instead of using fat-and-flour thickeners, modern chefs prefer to reduce the stock until the veal's own gelatin creates a dense, smooth, viscous liquid. This takes about four to five hours of aggressive simmering, and, near the end, straining and transfer to a smaller pot to prevent potential scorching.
Once two to three cups are left, I make another ice bath for the same reason -- get the temperature down quickly!
After ice and fridge, the demi glace is amazingly thick and solid. Like jello, except more dense. Almost like rubber, or one of those squeeze-stress-balls.
From there, I pick two or three one-cup storage containers, divide the demi glace, and freeze.
If tasted straight and warmed, the stuff is a little salty (though there was no salt added -- it's a concentration from the bones, tissue, and the canned tomato paste) but nothing like bullion. It's meaty, but a little slippery in mouth feel due to the concentration of gelatin. Used in a sauce, it distributes itself throughout the liquid and gives that subtle edge that makes a standard sauce a little more elegant.
As an epilogue, there's a French term called remouillage where veal bones can be re-simmered in water to make a secondary stock. These bones aren't finished even after 20 hours. I made a remouillage by taking the best quality of the leftover bones (about eight pounds worth), then putting them in my 10-quart stockpot and adding more water and fresh vegetables. I didn't add any tomato paste this time, because I was after straight veal stock, not espagnole. After another 20 hours and a chill to remove fat, I had sixteen cups of veal stock. I put one cup each into individual 9oz storage containers, and I now have a sixteen containers of veal stock, and three containers of demi glace, from the same ten pounds of veal bones.