The classical French clear soup or pot-au-feu is prepared in the following manner: Put a piece of beef in cold salted water, bring slowly to the boil and skim well. Then add the vegetables:
The proportion are four pounds of beef, including a piece of shin bone to eight pints of water; the pieces of chicken are to be put in with the vegetables. The water must be brought very slowly to the boil. The effect of this slow heating of the water is to dissolve certain albuminous matter which come to the top and form the scum; this scum must be removed regularly and frequently, and when the water approaches the boiling point, it is advisable to add a tablespoonful of cold water, which will help the process. The more scum you “produce” and the more you remove the clearer your consommé will be; but if you do not take this little trouble at the beginning nothing, done later, will clarify it properly.
Also the consommé would not be properly flavoured as the essential juices, kept back by the matter which ought to have come out as scum, would remain in the meat which would, also as a result, be tougher, should you want to use it.