The liquid inside the can is salty, starchy, and has a distinctive flavor. Beans that are not rinsed bring this flavor and salt directly into the recipe; they cloud salads, thicken sauces unexpectedly, and throw off the salt balance. Rinsing them under running water in a colander for half a minute removes most of it. Some recipes, however, intentionally use the canning liquid.
The liquid in a can of beans is not just water. It contains salt, starch dissolved from the beans, and a distinctive flavor developed during canning. When you open the can, the liquid looks thick, slightly gel-like, and cloudy. Added directly to a recipe, it brings three things at once: extra salt, an unwanted texture, and that familiar canned flavor. That is why canned beans are not an ingredient to use straight from the can. Recipes that use canned beans therefore often include a separate rinsing step.
Salt is the part most easily overlooked. The liquid in most brands is noticeably salty; using it without draining it throws off the recipe's salt balance from the start and makes the dish taste salty. Rinsing removes a significant portion of this salt. So in recipes using canned beans, salt is added at the very end and adjusted by tasting; salt added at the start cannot be taken back out. The salt content is listed on the can's label and varies noticeably between brands. Low-sodium or no-salt-added cans are also available, and the label identifies them.
The second issue is appearance and texture. The starchy liquid leaves a cloudy layer at the bottom of a salad and keeps dressing from clinging to the leaves. In hot dishes, it thickens the sauce unexpectedly; the dish comes out thick, but the texture has not been controlled. Rinsed beans, on the other hand, stay clean and separate, leaving the cook in control of the final texture. The same cloudiness occurs in hot dishes, too; soup takes on a duller color than expected. So if you want clear soup, never skip the rinsing step.
Rinsing is quick and simple. Empty the can, transfer the beans to a colander, and rinse them under running water for about half a minute, stirring them by hand. The job is done when the water running through the colander clears and stops foaming. Then let the beans drain for a few minutes; wet beans make salad watery. If you are going to fry or sauté them, pat them dry with a towel as well. Choose a wide colander so the beans spread into a single layer and water reaches every surface. Shake the colander a few times while draining to help the remaining water run off faster.
There are known exceptions. Some soup and stew recipes intentionally use the canning liquid because it provides body. Chickpea liquid is a separate ingredient and is set aside to whip into foam. In these cases, drain the liquid into a separate container and still rinse the beans. If the can itself is swollen, rusty, or dented, discard its contents without tasting them. After opening the can, do not leave leftover beans in it; transfer them to a covered container. Opened canned beans keep in the refrigerator for 3 to 4 days; if you notice an odor or foam before then, discard them without tasting.