Just the skin blackened can still be eaten. If the walnut kernel is still white and has not turned black or yellow, and the taste is not moldy or rancid, it can be eaten normally, but if the walnut kernel has also changed color, it must not be eaten anymore.
People who have eaten walnuts know that walnuts in fact really are two protective colors, one is the fresh walnut shell of the green skin, the second is the hard shell of walnuts. If the green shell or hard shell mold, you can open to see inside the kernel has not received the impact, if there is mold, black spots that can still be eaten.
And walnut shell outside is black is not necessarily moldy, some because of the previous peeling is not complete, residual in the walnut shell crevices left behind after weathering, the fruit flesh does not have any effect. So walnuts with black spots on the outer skin is not necessarily bad, but if there are white threads inside then it can not be eaten.
Expanded:
The reasons why walnuts turn black:
1, the outer skin of the oxidation reaction
Because the outer skin of walnut kernels contain a certain amount of polyphenols and flavonoids, these two substances in the presence of oxygen will occur in the oxidation discoloration reaction, which generally occurs in the state of walnut external breakage.
2, the outer skin by the disease
Walnuts in the picking process, it is easy to be attacked by disease, this time if the infection is black spot disease, whorl disease, etc., then the outer skin of walnuts will also appear to blacken the situation. For this kind of infected walnuts, it is recommended not to continue to eat.
3, save too long
Whether it is fresh walnuts or sun-dried walnuts, there is a certain period of preservation, fresh walnuts are best eaten as soon as possible, and sun-dried walnuts should not be stored for too long, otherwise it is likely to appear moldy or oxidative rancidity reaction, the longer the storage time, the longer the walnut's color will also become darker.
Phoenix - walnuts blackened can still eat it