Stored grain legumes can easily be infested with bruchids. These are small beetles whose larvae eat into the grain. The bruchids can be controlled simply by mixing the legumes with neem oil.
Neem oil is extracted from the neem seed kernels (oil content 40 – 50%). When used for storage protection it should be carefully pressed, either by machine or various other traditional methods. As only a very small amount of oil (30 ml oil per 100 kg grain) is required, pressing by hand is practicable. The seeds must first be shelled, by cracking the shells with a stone or gently pounding in a mortar and finally by winnowing to remove the shell particles.
If the crushed seeds are very hard and brittle they should be moistened and left to stand for several hours until they can be pressed together by hand. Crushing the seeds in a mill or mortar produces a rough, sticky mixture out of which can be pressed by kneading. Usually it is necessary to add a little water to make kneading easier.
By alternating kneading and pressing of the paste in a bowl the neem oil is released. Using this method it is possible to extract 150 ml oil from 1 kg powder. The legume seeds are treated with neem oil extracted in the following manner: The appropriate amount of neem oil is mixed with the legume seeds in a large bowl or similar container (3 ml per 1 kg grain); then the seeds may be stored in the usual way.
Neem oil is non-poisonous but very bitter, thus freshly treated legumes taste at first very sharp. This taste disappears, however, after 3 to 4 weeks.