Principles of stock making


Stocks are at the base of most of the Classic French, meat or fish sauces. Although, hygiene regulations have clamped down on their use in French and European kitchens, I am still a big fan of them.
In principle making a stock is extracting flavour and gelatine from meat, skin and bones.
First let’s have a look at the gelatine extraction process. Meat is made of water and the protein fibres that do the work of contraction which are not water soluble. The water soluble materials present in muscles are collagen which represents an average of 1% of the overall weight, other cell proteins for about 5% , 2% of amino acids and other savoury elements, 1% of sugars and other carbohydrates and 1% of phosphorous and potassium based minerals.
In the other hand, bones contains 20% of collagen, pig skin 30% and the chefs favourite source of gelatine veal knuckles and oxtail with 40%.
When meat is cooked in water for a long period of time collagen can be freed from the muscles connective tissues. The gelatine extraction time will depend on the type of bones and meat. Fish bones* and meats only require 20-25 minutes, for a veal calf and young ox tail it may take up to 4-8h, as for the bones and muscles of an old steer it will take longer, up to 24h. Note that the longer the extraction process lasts, the gelatine molecules that have already been dissolved into the water will gradually break down and become less efficient, later, when thickening a sauce (demi-glace) or form the strong matrix that will make a jelly (aspic).

The flavour extraction will gradually happen until the meat will reach the temperature of 70 degrees Celsius/ 160F. At that temperature the meat will have lost 40% of its weight in juices. These juices are made of water and water soluble savoury amino-acids.

What ingredients choose to obtain a full flavour and full bodied stock? Nowadays, when it comes to stock, chefs find themselves to have to balance flavour with economics. Meat is a great source of savoury molecules, but is very expensive and a poor source of gelatine. In the other hand, bones and pig skin is quite inexpensive and a great source of collagen but a poor source of flavour. So a good stock needs to have a good balance of meat (meat trimmings will do) and bones and/or pig skin. I like to use a proportion of 1/3 of meats for 2/3 of bones. Due to their cost, I would use veal knuckles for the making of aspic or savoury jellies, only.
Then, aromatic vegetables and herbs such as carrots, onions, garlic and celery, a bouquet garni will be added as well as some tomato pure and a bit of wine. I like to use some fennel instead of carrots in the making of fish stocks as carrots can make the stock turn a little bit orange.
In general, the solid ingredients are cooked in one to two times their weight of water. This makes 1-2 litres of water per kilograms of solid ingredients to start the stock.
Note that the smaller the meats are cut and the bones are broken, the faster their contents will be extracted into the water.

While cooking a stock must be kept as clear as possible to allow its use in the making of aspics, broths or consommés. I have to say, most of the work involved in stock making is to keep removing impurities from it (skimming). Depending on the type of stock, brown or white, the meat or bones are first roasted to develop the roasted meat flavour through the Maillard reaction for the brown stock or blanched for a minute or two, to remove all the surface impurities and coagulate surface proteins so that they won’t cloud the liquid, in the case of a white stock. Then, they are put in a pot alongside the vegetables and COLD water and slowly brought to a gentle simmer, and it stays there.
Now, comes the grim task of skimming and skimming and skimming again. This operation is necessary to remove the fat globules and scum from the surface.
It is important to start the stock with cold water and bring it slowly to a gentle simmer because it allows the soluble proteins to escape the meats and coagulate slowly into large aggregates that are going to be easily removed from the surface. A hot start and a strong boil will create small protein particles as well as smaller fat globules that will be kept in suspension and emulsion into the water by the boiling process, resulting into a cloudy liquid.
It is also important to keep the stock pot uncovered. This will allow water to evaporate and cool the surface; this will help controlling the gentle cooking process. It will also, dry out the surface scum, making it easier to skim. And it finally, starts the reduction process that will concentrate the stock’s flavour.
The final operation is, when cooked, to thoroughly strain the stock and get rid of most of its fat. For that operation, I think that the best way to do this is to cool down the stock and then remove the cap made of set fat, which will have formed on the top of the container.
This is then ready for use.

* Fish stocks as well as consommé made of crustaceans shells and heads(always had some fish bones when cooking such stocks as crustaceans don’t have any connective tissues on their shells), are made in the same way than mammals meats and bone based stocks. The only differences comes from the fact that due to the cold environment in which fish and crustaceans live their connective tissues and collagen differ from the land animals one. Fish collagen is less cross linked therefore it dissolve faster and at a much lower temperature. As it takes up to 24h at a gentle simmer to extract the collagen of an old steer, cod’s collagen and gelatine starts to melt around 10 degrees Celsius/ 50F.So the general rule when making a fish stock or fumet is to cook is around 70C/ 165F for about 20-25 minutes. This will result in a nice clear stock that can easily be made into a consommé. Note that fat fish bones and meats are not to be used to make fish stocks so avoid using bones from salmon, tuna, sardines, etc; prefer bones from black sole, halibut, cod, turbot and John dory.

1 comments:

  1. xhtml coding said,

    nice info

    on 11 October, 2008