What is the name of the kind of walnut whose kernels are difficult to peel

Walnuts with difficult to peel kernels are usually referred to as walnuts or iron walnuts. This type of walnut has a hard and thick shell, and the flesh is tightly adhered to the inner wall, requiring the use of tools to fully extract the kernels. The sandwich walnut stands in stark contrast to the cardboard walnut, with the latter being more favored by consumers due to its thin and brittle outer shell that is easy to peel. The shell of the walnut is dense in texture, with deep and irregular grooves on the surface, making it difficult to break open by hand. There is a fibrous partition between the lignified inner wall and the nut, which can easily cause the nut to break when peeled off. This type of walnut mostly grows in mountainous areas with dry climate and large temperature differences between day and night, and thick shells are an adaptive feature to the environment. Common walnut varieties include Yunnan iron walnuts, Xinjiang thick shell walnuts, etc. Although inconvenient to eat, the kernels have high oil content and rich flavor.

Paper skinned walnuts have been artificially bred to improve their shell characteristics, and can be cracked by pressing with the thumb. However, excessive pursuit of thin shell characteristics can reduce the disease and pest resistance of walnuts, and some thin shell varieties require specific cultivation techniques. From a nutritional perspective, there is no significant difference in the kernel composition between walnuts and paper skinned walnuts, both of which are rich in unsaturated fatty acids, vitamin E, and mineral elements.

When handling walnuts, soak them in boiling water for 5 minutes to soften the shell, and then apply longitudinal force to the walnut clip. Pay attention to selecting the parts with obvious gaps when using pliers, to avoid horizontal compression that may cause the nuts to shatter. If the walnut kernels have brown seed coat after shell removal, their antioxidant content is higher, but the taste is slightly astringent, and it can be removed according to the needs. Daily consumption of walnut kernels is recommended to be controlled within 20 grams, and those with weak gastrointestinal function should reduce their intake appropriately.