Walnut oil is a type of vegetable oil extracted from walnut kernels and falls under edible oils. Walnut oil is relatively scarce mainly because walnut kernels are more expensive compared to other oil-extracting raw materials, which also makes walnut oil relatively costly. Below, we will take a closer look at its related knowledge.

Walnut oil is considered a niche oil crop with limited annual raw material production. Its production cycle each year is not long; for small-scale oil mills, it is processed for only 2 to 5 months annually. However, due to the good quality of walnut oil and its favorable reception, more and more oil mills are producing and processing walnut oil. To meet market demand, walnut oil is mostly extracted using the pressing method. Crushed raw materials are adjusted for temperature and moisture and fed into an oil press where chamber pressure is adjusted and oil flow is smooth, thus producing green and healthy walnut oil.

Walnut oil extraction can be divided into cold pressing and hot pressing. Due to the high oil content and low fiber content of walnut kernels, their tissue structure and pressing performance are characteristic of soft oil materials. The friction coefficient between walnut kernel particles and between pressing material and the press cage wall is reduced, making internal transport within the press chamber difficult, and it is hard to build pressure during pressing.

In the cold pressing process, cell membranes are not broken, and the affinity between oil, oil-soluble substances, and proteins is strong. High pressure is needed to squeeze the oil droplets out from the cells, which is time-consuming and labor-intensive. In industrial production, in order to improve the production efficiency of oil mills, hot pressing is more commonly used to produce walnut oil. Walnut oil obtained by hot pressing has a fragrant aroma, deeper color, increased acid value, and an ideal oil yield that meets the production needs of oil mills.

However, the crude oil obtained by pressing contains a relatively high amount of impurities. Although most impurities are removed through settling, centrifugation, filtering, and other processes, walnut oil still faces issues such as higher acid value, darker color, and susceptibility to oxidation. Therefore, refining processes are needed to improve its quality and extend its shelf life. Walnut oil refining mainly involves multiple processes including degumming, deacidification, decolorization, and deodorization. Strict adherence to the refining steps during production allows for thorough separation of impurities from crude oil, resulting in a healthy and nutritious oil.