Many think of stock and think that making it simply means dumping a bunch of things into a pot and letting it simmer for hours. One could make a decent stock with that idea, but considering it makes the base for multiple dishes, it might be important to understand the science behind stock and the role of each ingredient being added. Some ingredients are added to clarify it, some are added primarily for flavour, while others are added to add body to the stock.
What kinds of stock are there?
There are two kinds of stock--white and brown. White stock is used to make velouté sauce and any sauces derived from the main velouté sauce, while brown stock is used to make demi-glace and its derivatives like bordelaise. The key difference between the two stocks is obviously the colour, with bones being blanched before simmering for white sauce and the bones being roasted before simmering for brown sauce.
What goes into stock?
Bones contain collagen which forms gelatin when simmered. The more gelatin in stock, the more body that stock will have. Ideally, there should be enough gelatin in the stock for it to solidify when chilled. Chicken, mutton, veal, pig bones all work very well to make stock since they have high quantities of cartilage.
Many people will allow the water to boil before they add other ingredients, but proteins like albumin only dissolve in cold water. Starting with cold water helps to release the albumin, which will give you a clearer stock.
Mirepoix sounds fancy, but it’s simply a combination of chopped onions, carrots, and celery added in a 2:1:1 ratio to add flavour and aroma to the stock.
Tomatoes are added to brown stock, both to add colour and add an acidic element to the stock which helps to break down the cartilage and other connective tissues in bones, which in turn helps in forming gelatin.
Wine is added to all kinds of white stock to add flavour and acidity.
Aromatics and additional flavour elements
Herbs and spices can be added to stock to add more flavour to the stock. You can either add them using a small cheesecloth sack filled with dried and fresh herbs and spices, known as a sachet d'epices, or a bouquet garni, where a bundle of herbs and aromatics tied with twine and added to the stock. Using a sachet d'epices or a bouquet garni ensures that they are easy to remove once the stock is done.
What else should I keep in mind when making stock?
Stock, when made for sauces, is reduced a lot. So salting the stock might result in your sauce becoming too salty, so either use very little salt when seasoning your stock or simply season the sauce when you make it.
If you’re adding ingredients with acidic elements to the stock, keep in mind that it reacts with aluminum. So it’s best to use a stockpot made of stainless steel.
To store stock, don’t bother filling a bowl with it and storing it in the refrigerator. Add them to ziplock bags or ice cube trays and simply freeze them. This way, when you need a small quantity of stock, like to make a sauce or for deglazing purposes, you can thaw only the amount you need.