Cassell's dictionary of cookery

A good-sized table-spoonful of this mixture, which is called, as we said, brown thickening, or brown roux, will, when mixed with half a pint or a little more of good stock, transform it into good rich brown gravy which only requires a few additions, varying with what the gravy is intended for, to complete it. If the gravy is intended for roast fowls, for instance, a little mushroom ketchup may be added ; if for game, such as a pheasant, a dessertspoonful of sherry. The effect of brown thickening in gravy is that not only is the gravy thickened and the raw flavour inseparable from butter and flour avoided, but that the important element — colour — is introduced or assisted. You may use half a dozen pounds of meat in making gravy, but if it comes up pale and thin it will be thought poor. The better the cooks the better do they understand the importance of appearances. Good thick mock-turtle soup owes its rich colour to this thickening, and it is because bi-own thickening is so rarely made, or the use of it so little understood in private houses, that home-made thick mock-turtle is so invariably poor, although the amount of real calves' head — and not pig's head — used in its preparation is probably double that used in an ordinary pastrycook's. One great advantage of having brown thickening is, that it is possible to make enough at once to last a couple of months. Gravy is constantly being wanted; and in the end the cook will find time saved by having the thickening at hand ready made, instead of the plate, the dab of butter, the mixing, the uncertainty as to quantity, &c., which is their usual wont in melting a little butter and flour fresh for each occasion, the reason they melt it together being very properly to avoid the constant stirring necessary to prevent the gravy or soup thickened turning lumpy. As, however, we are on the subject of thickening, by means of brown roux, soups, such as mock-turtle, gravies, &c., it may occur to some to inquire — How would you thicken white soup, such as Palestine soup, oyster soup, &c. ; or. How would you thicken cheap Bechamel sauce where no cream is used 1 Our answer is— By usuig white roux instead of brown. But then white roux or white thickening is not necessarily butter and flour just melted together, which, as we have said, has a tendency to give whatever is thickened a raw and gruelly flavour. The cook will have observed in making the brown thickening what a long time it took before it began to turn colour — in fact, her patience the first time was probably nearly exhausted, and she would very likely confess afterwards, flushed with triumph, that she began to think the "stuff" would never turn colourat all. White roux is simply, to use an Irish expression, brown thickening just before it gets brown ; or, in other words, the grains of raw flour are cooked, but not coloured. The difierence in flavour is as distinct as that of white pastry and dough.