Soup – Crunchy onions in soup

Sauteed onions can provide both caramel flavors (from the sugars in the onions) and Maillard reaction compounds, depending on how they are sauteed. Thus onions can supply a range of "umami" flavors for soup which otherwise you need to get through roasting animal bones and other tissue (e.g. brown veal stock). Of course, even beef stocks often add onion as well for extra flavor.

As an extreme example of this, I often prepare a vegetarian French Onion soup using a meat-free broth made entirely from onions, onion skins, and cheese rind. Blind tasters often fail to distinguish it from a store-bought beef stock.

You can get a lot of the same flavors from combinations of other browned vegetables, but onions neatly supply a perfect package of flavor compounds in one inexpensive, long-keeping root vegetable. Why use anything else?

It takes quite a while for a pot of hot soup to cool down to 40°F in the fridge. Several hours, sometimes, depending on the shape of the pot and the volume of soup. If you're heating and re-chilling the same soup daily, it's going to spend a lot of time in the danger zone. From a safety perspective, you'd be much better off making a pot of soup every few days and then reheating just the portion that you're actually going to eat.

I still recommend this money saving idea to current students

Soup is a great food for stretching a dollar, but I don't see how it's any more expensive to make a fresh pot twice a week and it shouldn't take much time either. I understand that you were adding scraps each night, but you could as easily save those scraps for a day or two until you make the next pot of soup.