When the weather cools down, walnuts tend to make their way back into the kitchen. They show up in banana bread, oatmeal, stuffing, salads and, if you have a walnut tree, possibly all over your yard.
Of course, no one wants to let perfectly good walnuts go to waste. But once you crack them open, there is sometimes that little surprise: a bitter bite.
Is that normal? Have the walnuts gone bad? And more importantly, should you still eat them?
Let’s get into it.
Short answer: sometimes walnuts are naturally a little bitter, and sometimes they are telling you it is time to let them go.
Walnuts have a thin brown skin, also called the pellicle, wrapped around the nutmeat. That skin contains polyphenols, including tannins, and walnut tannins can naturally taste bitter.
This is not necessarily a bad thing. Those same compounds are part of the reason walnuts are often talked about as a nutrient-dense food with antioxidant benefits.
Another common reason walnuts taste bitter is age. The older walnuts are, or the longer they have been sitting around after falling from the tree, the more likely they are to taste stale, sharp or rancid.
Walnuts are high in fats, especially polyunsaturated fats, which is one of the reasons they are such a heart-friendly nut. But those fats can also oxidize over time, and that is when walnuts may develop a bitter, sour, paint-like or “off” flavor.
A mild bitterness from the skin is normal. An overwhelmingly bitter, musty, chemical or spoiled taste is not something I would try to power through in the name of fiber.
Walnuts can also absorb odors from the foods around them. Store them near onions, spices or an open container of something fragrant, and do not be shocked if your walnuts start tasting a little less like walnuts and a little more like the inside of your refrigerator.
That is why proper storage matters. Keep shelled walnuts in an airtight container, and for longer freshness, the refrigerator or freezer is usually a much better choice than the pantry.
This is where your senses come in handy. A walnut with a slight bitter edge, especially from the skin, can still be perfectly fine.
A bad walnut usually has more going on than bitterness. Look for a rancid smell, a sour or paint-like aroma, shriveled nutmeat, dark spots, visible mold, a rubbery texture or a taste that makes you immediately question your life choices.
Fresh walnuts should smell mildly nutty and a little earthy. They should not smell like old oil, musty cardboard or a forgotten bag of trail mix from 2019.
When in doubt, throw them out. I know, food waste is annoying, but so is eating something that clearly waved a red flag at you.
The walnut skin is where most of the natural bitterness comes from. Removing at least some of it can make walnuts taste sweeter and smoother, especially if you are using them in desserts, sauces or salads.
That said, the skins will not always come off perfectly. Walnuts have folds and creases, and those little brown bits like to hang on for dear life.
Two of the easiest ways to loosen the skin are blanching and roasting. Both can help mellow the bitterness, though roasting usually gives you the bigger flavor upgrade.
To blanch walnuts, bring a pot of water to a boil. Add the shelled walnuts carefully, because splashing boiling water around the kitchen is not the kind of excitement anyone needs.
Let the walnuts simmer for about one minute, then drain them well. Spread them on a clean towel or baking sheet and let them dry completely.
Once dry, rub the walnuts gently with a clean kitchen towel or paper towel. Some of the skins should loosen and flake off.
Do not try to rub them while they are still wet unless you enjoy sticky walnut skin clinging to your fingers. Personally, not my favorite kitchen activity.
Roasting is my favorite option because it not only helps reduce bitterness, but also brings out that warm, nutty flavor walnuts are supposed to have. The trick is not to overdo it.
Preheat the oven to 325 degrees Fahrenheit. Spread the shelled walnuts in a single layer on a baking sheet lined with parchment paper.
Toast for about 7 to 10 minutes, stirring or shaking the pan once halfway through. Keep a close eye on them because nuts can go from beautifully toasted to “well, that’s ruined” very quickly.
The walnuts are done when they smell fragrant and look slightly deeper in color. Let them cool completely, then rub them in a clean towel to remove some of the loosened skins.
The skins will not come off entirely, and that is fine. Your walnuts should still taste less bitter and much more pleasant than they did straight from the shell.
Walnuts can absolutely be part of a healthy diet. Research has linked walnut intake with potential benefits for heart health, inflammation and overall diet quality.
They are also a good source of plant-based protein, fiber, magnesium and omega-3 alpha-linolenic acid. Basically, tiny nutrient bombs, which is probably why they show up in everything from breakfast bowls to holiday stuffing.
But rancid or moldy walnuts are a different story. Unlike a fuzzy strawberry or a clearly moldy piece of bread, mold or spoilage in nuts is not always easy to see.
The first clues may be smell and taste. A walnut that is extremely bitter, musty, stale or sour should not be eaten.
Mold exposure can be a concern with many foods, including nuts, especially when they have been stored in warm or damp conditions. Some molds may produce mycotoxins, and mycotoxin research has shown that certain types can be harmful to the liver, kidneys and overall health.
This does not mean every bitter walnut is dangerous. It does mean that walnuts with an intense bitter taste, foul smell or signs of mold are not worth the risk.
Store-bought walnuts can also spoil faster if the package has been opened, exposed to heat or kept in the pantry too long. Walnuts from your own tree need to be handled carefully too, because moisture is exactly what mold loves.
After harvesting walnuts, remove any green hulls, discard nuts that look moldy or damaged, and dry the walnuts in a cool, dry, well-ventilated place. As noted by the University of California Agriculture and Natural Resources, proper harvesting and drying are important for walnut quality.
Because walnuts contain delicate oils, they do best away from heat, light, moisture and air. In other words, the decorative bowl on the sunny kitchen counter is cute, but not ideal.
For shelled walnuts, use an airtight container and store them in the refrigerator or freezer. The USDA FoodKeeper is a helpful resource for general food storage timelines, and nuts typically keep much better when chilled or frozen.
In-shell walnuts can last longer than shelled walnuts because the shell gives them some natural protection. Even then, they should still be stored in a cool, dry and dark place.
Keep walnuts away from strong-smelling foods. Nobody is asking for walnuts with a hint of garlic, unless maybe dinner has gone completely off the rails.
Also, try to keep walnuts whole until you are ready to use them. Chopping or grinding increases the surface area, which means the oils are exposed to more air and can turn rancid sooner.
Have walnuts you need to use before they lose their charm? Good news: walnuts are one of those ingredients that work in sweet, savory and snacky situations.
Here are a few easy ways to use them:
And yes, if you have shell-on walnuts that you truly are not going to eat, you can still get creative. Painted walnuts can be used for holiday decorations, place settings or Christmas ornaments.
Is that nutrition advice? Not exactly. But it is a lot better than letting a whole bowl of walnuts sit around until they taste like sadness.
Walnuts can taste bitter for two main reasons. The first is totally normal: their thin brown skins contain tannins and other polyphenols that naturally have a bitter flavor.
The second reason is less charming: the walnuts may be old, rancid, moldy or poorly stored. Mild bitterness is usually fine, but a strong bitter, sour, musty or chemical taste is your sign to toss them.
To make walnuts taste better, try roasting or blanching them, and store them in an airtight container in the refrigerator or freezer. And when possible, keep them whole until you are ready to use them.
Walnuts are too good, and too nutritious, to waste. They just need a little care so they taste nutty, fresh and delicious instead of bitter in all the wrong ways.
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