Though this is the easiest and most home-chef friendly of the classical stocks, don’t let that fool you. Vegetable stock is extremely useful stuff, and making it is one of the better tricks a home chef (particularly a vegetarian/vegan) can have in their culinary arsenal. It’s great as a base for vegetarian soups or as a medium for reconstituting dried mushrooms.
1. Select your vegetables
A blend of onions, celery, and carrots (aka mirepoix) will provide a good backbone for your stock, imparting flavor and depth without releasing any strong single flavor or coloring the stock. Beyond that, really any vegetables can be used to make stock within certain parameters. Avoid starchy vegetables if you want your stock to remain clear rather than cloudy. It’s also best to avoid spinach, cabbage, artichokes, cauliflower, and Brussels sprouts as these veggies release nasty flavors when cooked for a long time. Vegetable stock is a great way to extract flavor from vegetable trimmings that you may have left over from other recipes. We routinely set aside trimmings, freeze them in a zip loc and then have them on hand for veggie stock. Talk about recycling!
2. Roughly chop vegetables into uniform size chunks and (optional) sweat in oil
To “sweat” vegetables means to use low heat to help release some of their moisture and remove some of their uncooked flavor. No color should be gained from a sweat. If you’re caramelizing your veggies even a little bit your heat is too high. Usually salt is added to a sweat to help draw moisture out, but this conflicts with one of the cardinal rules of stock making so don’t do it here. For a little extra flavor you can use butter instead of oil, but of course doing so will keep your stock from being vegan-friendly.
3. Fill your stockpot and bring to a simmer
Put your water, vegetables, and a bouquet garni or sachet in your stock pot, and heat until it reaches a simmer. Keep an eye out for any scum that develops on the surface and needs to be skimmed (with a veggie stock this shouldn’t really be an issue).
4. Simmer 30-45 minutes
That’s really all the time it takes to get the best from your vegetables. Any longer than that and you risk them breaking down into your stock or developing unpalatable flavors.
5. Strain and drop your stock
Strain your stock through the finest strainer you’ve got (with cheesecloth added if necessary) and quickly reduce the temperature (“drop”) through the use of an ice water bath. For further explanation of stock dropping, refer to the cardinal rules of stock making.
6. Store until ready to use
Stocks store in the fridge for about 2-3 days refrigerated (assuming you dropped them correctly) and will freeze wonderfully for several months.