Great care needs to be taken when adjusting the consistency of soups. Whatever the reason for the adjustment – whether the soup is too thick or too thin – the flavor must always be considered. Either thinning down or thickening a soup will effect its final flavor whatever the method used.
Purée of vegetable soup may be adjusted, if too thick, by the addition of white stock. Those that are too thin may be adjusted by the addition of a purée of the same type of vegetable from which the soup is made, or if none is available by adding a small quantity of potato powder or granules. Diluted arrowroot or rice flour may also be used as a thickening agent, but the soup in question must be allowed to cook through for a time in order to avoid either a glassy appearance or a slight rawness of taste.
Creams and veloutés may be adjusted, if too thick, by the addition of more of the same white stock used in the recipe. Those that are too thin may be adjusted by the addition of béchamel in the case of cream soups, or velouté in the case of the latter. Extra liaison of cream or egg yolks and cream may be used but only as a last resort because of the costs involved.
Fawn and brown roux-based soups may be adjusted if too thick by the addition of more of the same type of stock used in the recipe. Those that are too thin may be adjusted by adding some extra thick basic sauce – velouté for fawn roux-based soups (in which case some degree of color adjustment may be necessary), and basic brown sauce for brown roux-based soups. Alternately diluted arrowroot may be used to adjust them but it should be used sparingly and must be allowed to cook through to avoid any other distortion of the soup.