Why remove the vegetables from vegetable stock? [duplicate]

The point of stock is to extract the maximum flavor from whatever you are using, be it bones or vegetables. Once extracted there's not a whole left, which is why you don't boil stock bones over and over. Vegetables will not have much left to give after being used for stock, you can still eat them but they may not be flavorful or nutritious.

Unless you're making a stew you're going to be cooking the stock, then removing the vegetables, then cooking the stock more with other ingredients. If you leave the vegetables in they'll continue to cook until they break down, and that's usually undesirable.

If you are making a dish where you want to eat the vegetables with it then you would either want to extract them while they still have some texture and then add them back in at the end to re-heat, or add them towards the end and cook them till done.

You could, but...

With them in, the texture and appearance will be rather different - the stock will be thicker and cloudier, stock or resulting broth, you can't go adding more like a thin sauce or a soup. That's fine if it's what you want, but if you want a fairly clear thin broth around your noodles, you don't want mushy grated veg in there - but you may well want to add some finely chopped, quickly fried mirepoix.

You also try to extract as much flavour into the stock as possible, so leaving as little as possible in the veg. If you use herbs in your veg stock, you may have to hunt down woody bits at some stage.

Certainly consuming the veg is economical, and a source of veg in your diet, so from that point of view there's no reason not to give it a try and see what you think. It may be better for some dishes than others, so if you make a batch that way and don't like it for noodle broth, try it in something else

Why remove the vegetables from vegetable stock?

It's likely the concept of "mushy vegetables" that throw people off. The texture of overcooked vegetables isn't the best, and the vegetables will eventually lose their vibrant colors and become grayish/brownish.

As you continue to cook the vegetables, they will start to break down, and un-sightly bits will start to float around in the stock. All those factors may contribute to the filtering out step in the recipes, but at my household, that would be too wasteful.

I'm specifically thinking of ways to try and add flavour to the broth of vegan noodle dishes...

If you don't already, I highly recommending you try using dried aromatic ingredients, such as shiitake mushrooms and whole peppercorns; we use them (as well as some other ones) every time we make stock.

I recommend you try it once ;) you will often find that the remaining soggy husk of the vegetables you started with negatively affects the overall dish.

If you boil it for long enough some vegetables will eventually dissolve, but many brake down leaving fibrous and comparatively tasteless remains.

Much flavour is stored in the fats and lipids and other liquids within the vegetables or otherwise between the fibers, the general mechanism in creating a stock is to raise the temperature to a point where these can be dissolved out of the vegetable and then we want to separate the flavour from the fats themselves and extract it into the liquid, thus physically removing all these elements from the original produce.

Think about it from a mechanical point of view, the raw vegetable is made up of these tiny packages of flavour, these packages are then stored within more layers of tight packaging, the stock process has to break apart all those tiny packages to extract the goodness, what it leaves behind is simply a mess of shattered packaging materials.

Onion and celery are really good examples, even when the final dish expects these elements and you are creating this stock specifically for this dish, you would remove what remains of the stock base ingredients and add in fresh vegetables for this dish itself.

Try it once, this is an art form after all. In certain dishes, it may add a desirable texture, but it is not usually so.

Keep in mind that if you are preparing your stock to store for later that the fibrous material left behind will provide a safe harbour for bacteria to form and multiply, it creates temperature differentials and the organic material will start to rot causing the rest of the liquid to spoil much sooner than it would have if you had sufficiently filtered it first.