How to Make Vegetable Stock from Scraps

Choose scraps with flavor, not bitterness

The best vegetable stock starts with scraps that are clean and fresh. Keep a freezer bag in your kitchen and add onion skins and ends, carrot peels, celery leaves, parsley stems, mushroom stems, and the trimmed tops of leeks or fennel. A little variety gives the stock depth without making it taste like one vegetable.

Skip scraps that are moldy, slimy, heavily dirt-covered, or strongly bitter. Brassica trimmings like cabbage cores, broccoli stems, and cauliflower leaves can work in small amounts, but too much can make the stock sulfurous. Beet peels can make it muddy and sweet, and potatoes can make it starchy and cloudy. Save those for dishes where their flavor fits better.

Build the pot before you turn on the heat

For one standard batch, use 6 to 8 packed cups of scraps and add 10 cups cold water. If your scraps are mostly mild vegetables, add one quartered onion and one carrot to round out the flavor. If you have them, include one celery stalk, 6 to 8 peppercorns, and 1 bay leaf. Avoid salting the pot at this stage; stock is easier to season later than to fix when it is already too salty.

Use a heavy saucepan or Dutch oven, a cutting board, a chef's knife, and a fine-mesh strainer. If your scraps are frozen, you can put them straight in the pot from the freezer. There is no need to thaw them first. The pot should look full but not crowded, with enough water to cover the vegetables by about an inch.

• Aim for a loose mix, not a pot packed with only onion peels.
• Keep garlic light. One smashed clove is enough if you want it.
• Reserve tender herb leaves for garnish. Stems hold up better in stock.

Bring it up gently, then hold a bare simmer

Set the pot over medium-high heat until the water just begins to steam and small bubbles break at the edges. As soon as it reaches a simmer, lower the heat so the surface stays calm, with only an occasional bubble rising. A hard boil agitates the vegetables and can make the stock cloudy and bitter.

Simmer delicate stock for 45 minutes if you want a lighter flavor, or 60 to 90 minutes for a deeper result. Stir once or twice during cooking, mostly to check that nothing is sticking. The stock is ready when the kitchen smells savory and the vegetables have given up their color and aroma, but before they collapse into mush. If the liquid level drops a lot, add a splash of hot water rather than letting the pot boil dry.

• Visual cue: the surface should tremble, not roll.
• Visual cue: onion skins will fade and carrot pieces look pale and soft.
• If the stock tastes flat at 45 minutes, give it another 15 to 20 minutes.

Strain cleanly and cool it quickly

Remove the pot from the heat and strain the stock through a fine-mesh sieve into a heatproof bowl or another pot. For a clearer stock, line the sieve with cheesecloth. Let it drain on its own instead of pressing hard on the vegetables; squeezing can push fine sediment and bitterness into the liquid. Discard the spent scraps once they stop dripping.

To cool safely, divide the stock into smaller shallow containers so it loses heat quickly. You can also set the container in an ice bath and stir occasionally. Once the steam stops and the stock feels warm rather than hot, move it to the refrigerator. Do not leave it on the counter to cool for hours.

Sources: FoodSafety.gov: Four steps to food safetyFoodSafety.gov: Cold storage chart

Taste, adjust, and fix common problems

Vegetable stock should taste savory and balanced, but not aggressively seasoned. A good stock is a base, not a finished soup. If you want more depth, simmer the strained stock for 10 to 15 minutes longer to reduce it a little. If it tastes too strong, dilute it with hot water in small additions until it is useful again.

The biggest mistakes are overloading the pot, boiling too hard, and adding too many strong scraps at once. If the stock tastes bitter, the cause is usually too much cabbage-family vegetable or overcooked herbs. If it tastes dull, add a few fresh parsley stems, a little celery, or a peeled onion quarter and simmer briefly. If it comes out cloudy, strain it more gently next time and avoid stirring the pot after the boil starts.

• Too salty: do not salt the stock early; season the finished dish instead.
• Too dark: you used a lot of onion skins or roasted scraps; dilute or use it for a darker braise.
• Too thin: simmer uncovered a little longer after straining.
• Too bitter: reduce brassicas, garlic, or herb stems in the next batch.

Store it in portions you will actually use

Refrigerate vegetable stock within 2 hours of cooking, or within 1 hour if the room is above 90 F. Keep your refrigerator at 40 F or below, and use refrigerated stock within 3 to 4 days. Label containers with the date so you know what to use first. For longer storage, freeze the stock in jars with headspace, silicone cubes, or zipper bags laid flat so they stack easily.

Thaw frozen stock in the refrigerator, in the microwave, or directly in a pot over low heat. Do not thaw it on the counter. When you reheat stock for soup, sauce, or grains, heat it thoroughly before serving and bring it back to a simmer before using it in another dish. If you keep a scrap bag in the freezer, refill it as you cook so the next batch is waiting when the bag is full.

Sources: FoodSafety.gov: Four steps to food safetyFoodSafety.gov: Cold storage chart