I've said it before and I'll say it again: soup is my favorite thing to make for mid-week lunches and dinners. Soups optimize the healthy/filling/cheap/delicious quadrangle better than any of my other top lunch picks, as illustrated by this handy visual aid:
Most recipes call for some sort of flavored stock base, and while the store-bought liquid usually tastes great, it will typically run you about $2.99 per liter for the good stuff. This can seriously add up if you're putting together a brothy soup and is an unreasonable expense if the rest of your ingredients are relatively cheap. And the unhealthy-yet-still-tasty dry powder and cubes are usually loaded with questionable ingredients like MSG (even if it's labeled otherwise) and ungodly amounts of sodium.
The best way around this, of course, is to make your own stock. And for the most part you can do this using your cooking trash. I like to save the plastic bags from carrots or celery to add food scraps from normal day-to-day cooking, keeping the bags in the freezer when they're not in use. When you have about two or three full bags, you can add the frozen scraps to a large pot, fill until covered with water, add seasonings, simmer for a few hours, and you're in business. The more soup you make, the more scraps you'll have; it makes for quite a nice little self-perpetuating cycle.
But some scraps and seasonings are more equal than others when it comes to stock flavoring. Here are some tips from my years of trial and error for creating the cheapest, most flavorful stock that requires the least amount of work and dishes:
1. Good food scraps
Meat bones are great (even buffalo wing remnants!) and are sold very cheaply at the butcher counter. Good veg include onion peels, carrot ends and skin, celery ends and wilted pieces (including the leafy center), green parts and ends of leeks, spring onions, rinsed old mushrooms, stems of fresh herbs, the peel and knobby bits from fresh ginger, garlic, and the rinds of Parmesan or other hard cheese.
2. Bad food scraps
Squash and citrus peels are very bitter, all cruciferous vegetables taste rancid and smell like farts when you cook them for a long time, and anything with a high water content will completely disintegrate and discolor the stock (think spinach, lettuce, tomatoes, zucchini).
Most of these ingredients make for a great soup, but do not hold up well to long cooking. Except the citrus peels of course. Still not sure why I thought that was a good idea.
3. Good seasonings
A couch surfing hippie once taught me that a splash of vinegar will really extract the maximum amount of flavor from your stock. Actually I think he referred to magic collagen juju and not flavor specifically, but according to the internet, this isn't a completely baseless idea.
Whole spices will also add great flavor to the liquid (about 1/2-1 teaspoon of each will do); for maximum benefit, smash the spices using the flat side of a knife before adding them to the pot. I always use black peppercorns, cloves (secret stock ingredient!), and bay leaves. Dried chiles, cinnamon sticks, fennel seed, star anise, and coriander seed are also great additions.
4. Bad seasonings
Ground spices and crumbled, dried herbs will add great flavor, but will also make your stock look dirty and give it a grittier texture since the small bits can't be filtered out unless you want to stuff around with multiple layers of cheesecloth or muslin and make a big mess. Depending on the type of soup you want to make, this might not matter (eg. this would be fine for a thicker dark-colored soup). I certainly agree with the Guardian: "personally, I reckon life's too short for consommés."
5. The question of salt.
I never add much salt to the stock itself, only to the dish I use it in, tasting as I go. This is totally a personal preference, but I think it's much easier to control this way and you don't have to worry about the liquid over-reducing. It's really easy to let sodium levels get completely out of hand when making soup, especially when using canned ingredients. See Tip 10 regarding semantics and the non-necessity of preparing stock to be enjoyed on its own.
6. Consider your end goal.
I have made the mistake before of putting absolutely every scrap and seasoning I could find in the stock pot. The result was something sort of bitter, sort of spicy with Asian flavors, and sort of cheesy. Not recommended. But some combinations that do make sense:
-All-purpose flavor base: Stick with the meat and onion/carrot/celery/leek/parsley scraps, and season with garlic, black peppercorns, whole cloves, and bay leaves.
-For a potato or cream-based soup: Add cheese rinds and fresh dill stems.
-For chili or other bean stew: Add dried chiles, coriander and cumin seeds, and fresh coriander and oregano stems.
-For braising meat: Add fennel seeds, star anise, fresh rosemary and thyme stems.
-For an Asian flavor base: Add the hard unusable parts of lemongrass stems, dried chiles, fresh ginger peels, star anise, and fresh coriander stems.
7. To brown or not to brown?
Some stock recipes suggest roasting or sautéing the vegetables and bones to brown them and generally develop a more complex flavor before adding water. I'm definitely opposed to roasting on the basis that it creates another dirty dish (and cleaning roasting pans is the worst), and I'm also opposed to using fresh ingredients instead of scraps to make a broth. Most soup recipes start off with sweating onions or some such anyway, why do it twice and why discard perfectly good vegetables?
Having tried it, I can say that the flavor difference is not measurable . I am however intrigued by the easy-sounding German technique of slicing an onion in half and browning it before making stock. Warrants experimentation.
The stock has to cool completely before refrigerating, so I will usually leave the covered pot out overnight to come to room temperature and strain and containerize in the morning (I've also forgotten and left veg stock out at room temperature for several days - still fine). One-liter reused yogurt or clear takeaway containers are my favorite storage units and they conveniently hold the same amount as the cartons in the supermarket.
I've never found a need for piddly plastic baggies or ice cube trays as recommended by some that expose the stock to the rest of your freezer's smells. Need a quick defrost? Microwave it for a minute to loosen the frozen cylinder and dump the rest into your soup pot. The burner will do the work for you.
9. Meat means more work.
Stock is a great use for your leftover carcasses from a Sunday roast, but the fattiness will add an extra step to the process since, unlike vegetable stock, you can't just strain the liquid and stick it in the freezer. Return the strained liquid back to the pot and stick it in the refrigerator for a few hours to cool. A white layer will solidify on the top that you can easily remove to de-fat the stock before freezing or using. If you want to go really full circle, you can use the fat in any number of other delicious recipes.
10. A note on semantics
The Kitchn does a great job at summing up the difference between broth and stock. Basically broth is something that you can eat on its own with rich flavors, seasonings, and meat (not just the bones) while stock is more of a concentrated base on which to build a dish. Many broth recipes call for fresh meats and veg which you cook to extract flavor and then discard, which, like the browned components in Tip 7, seems to me like a waste of perfectly good soup ingredients. So use the bits you discard anyway to make stock, then add other ingredients and seasoning to finish the soup. It's just plain efficient.
Want to give it a shot? Here are some of my favorite stock-based recipes on the internet:
Carrot, Kumara, and Ginger Soup
Curried Split-Pea Soup
Super Delicious Zuppa Toscana
Hot and Sour Soup with Ginger
French Onion Soup