what is the reason for adding tomato paste when making a brown stock? I'm studying for an apprenticeship test and I know one of the questions is about why you add tomato paste to brown stock.  I have been taught that it's for depth of flavour and colour.  However, the choices on the test are separated into a) flavour, b) colour, C) acidity d) to speed up cooking process (?!)  I'm curious if anyone knows the actual ONE reason we add tomato paste to the bones?
It's odd that they force you to choose one, as many things in cooking have multiple reasons, e.g. browning meat adds flavour and colour to a stew. Are you sure the question isn't one of those 'tick all that apply' ones?

In this case, the tomato paste adds flavour, colour, and the acid helps break down the connective tissue in the bones, which helps the stock to jellify.