Vegetable stock is one of the easiest things to make from scratch and it doesn't require you to buy a single thing as long as you collect your kitchen scraps for a couple weeks.
This is something that I make every few weeks when I've gathered up too many scraps and need to make room in my freezer. You can either freeze it when it's done or you can use it in all your meals for the next few days - especially if you love soup as much as I do!
Collect Vegetable Scraps
The first thing you need to do is collect enough vegetable scraps and freeze them. The more vegetable scraps you collect, the better it's going to be. If you don't have enough, it may end up tasting a bit too watery. My crock pot is 6 quarts so I like to use 2 1-gallon freezer bags worth of scraps at minimum- but really I just put scraps in it until it's filled almost to the top. Sometimes that's more and sometimes that's less- depending on what types of scraps I collect.
Vegetable scraps are exactly what they sound like - all the parts of the vegetable that you didn't use in your cooking. Carrots, onions, and celery are the "holy trinity" ingredients of the stock - or as their known in French, the Mirepoix. Most (9/10) of your veggie scraps should come from these 3 - that means carrot peels & tops (carrot tops but not the leaves) , onion peels, tops & bottoms, and celery leaves, tops & bottoms of the stalks. Other vegetables that you can include in very small quantities (less than 1/10 of all ingredients) are fennel, bell peppers (no seeds), tomatoes (no seeds), asparagus, shallots, scallions, mushrooms, leeks, chives, and chard. Do not use any rotten parts of the vegetables.
There are some vegetables that you definitely do not want to add. You want to avoid anything that can add a bitter taste such as leafy greens and anything starchy which can make your stock thick and cloudy. Do not add sweet or white potatoes, beets, bok choy, broccoli, cabbage, kale, collard greens, corn, or radish.
Herbs and Extra Flavors
Adding in fresh herbs in small quantities isn't necessary, but will definitely give your broth more flavor. I like adding in some fresh thyme and parsley.
If I don't have any fresh herbs on hand, I just throw in dried herbs and that works, too. You can also add rosemary or cilantro - but only in very small quantities as their flavors can be overwhelming. Focus on 1 or 2 herbs maximum for your stock as you don't want too much going on that you can't taste each herb individually. If you're using cilantro, I wouldn't mix that with any other herb. My personal favorite herb to add which isn't overpowering and is especially good for soups is thyme.
Garlic is a must-have for my own stock, but some people think the flavor can be too overpowering. I add the garlic scraps I've collected (skin, bulb bottoms) and also some fresh cloves.
Want to add a little twist to your stock? Add some fresh ginger! This will give it a little bite and is especially good for soups.
I decided to try and add some heat to the last batch I made since I was going to be making Tortilla soup out of it and I added 1 full Scotch Bonnet pepper. It added just a little bit of heat - and it was phenomenal!
Adding in a few shakes of salt and pepper are good as well, but not necessary.
Cooking Methods and Extracting Maximum Flavor
Rule of thumb: the longer you cook it, the better it's going to be. Some people insist on sautéing the vegetables in a pot with a little butter or olive oil to begin the flavor extraction process. Since I cook my stock for a minimum of 24 hours, I don't find this step to be necessary.
Since you do want to cook your stock for a long time, I suggest using a crock pot and cooking it on low. I like mine to cook for 24 hours. After that, strain it with a cheese cloth or very fine strainer into containers. You can either freeze it or put it in the fridge and use it up in the next few days.
If you don't have a crock pot, you can cook it in a pot on low heat with the lid on. Of course, you would have to tend to the stove so you may not be able to cook it for 24 hours, but a minimum of 8 hours will extract lots of flavor.
Just dump your vegetables in the pot, fill it the rest of the way with water, and watch as the magic happens! Over time it'll turn into a gold color and if you let it cook a full 24 hours, it may even develop a deep golden brown color - that's when I know my stock is done.
Once it's done, strain the stock into a container using either a cheese cloth or a very fine strainer. The finer the strain, the better.
And that's all! There are so many things you can use stock for. It's full of nutrients, flavor, and is completely waste-free!